    const std = @import("std.zig");
    const builtin = @import("builtin");
    const debug = std.debug;
    const assert = debug.assert;
    const math = std.math;
    const mem = @This();
    const meta = std.meta;
    const trait = meta.trait;
    const testing = std.testing;
    const Endian = std.builtin.Endian;
    const native_endian = builtin.cpu.arch.endian();

    /// Compile time known minimum page size.
    /// https://github.com/ziglang/zig/issues/4082
    pub const page_size = switch (builtin.cpu.arch) {
        .wasm32, .wasm64 => 64 * 1024,
        .aarch64 => switch (builtin.os.tag) {
            .macos, .ios, .watchos, .tvos => 16 * 1024,
            else => 4 * 1024,
        },
        .sparc64 => 8 * 1024,
        else => 4 * 1024,
    };

    /// The standard library currently thoroughly depends on byte size
    /// being 8 bits.  (see the use of u8 throughout allocation code as
    /// the "byte" type.)  Code which depends on this can reference this
    /// declaration.  If we ever try to port the standard library to a
    /// non-8-bit-byte platform, this will allow us to search for things
    /// which need to be updated.
    pub const byte_size_in_bits = 8;

    pub const Allocator = @import("mem/Allocator.zig");

    /// Detects and asserts if the std.mem.Allocator interface is violated by the caller
    /// or the allocator.
    pub fn ValidationAllocator(comptime T: type) type {
        return struct {
            const Self = @This();

            underlying_allocator: T,

            pub fn init(underlying_allocator: T) @This() {
                return .{
                    .underlying_allocator = underlying_allocator,
                };
            }

            pub fn allocator(self: *Self) Allocator {
                return .{
                    .ptr = self,
                    .vtable = &.{
                        .alloc = alloc,
                        .resize = resize,
                        .free = free,
                    },
                };
            }

            fn getUnderlyingAllocatorPtr(self: *Self) Allocator {
                if (T == Allocator) return self.underlying_allocator;
                return self.underlying_allocator.allocator();
            }

            pub fn alloc(
                ctx: *anyopaque,
                n: usize,
                log2_ptr_align: u8,
                ret_addr: usize,
            ) ?[*]u8 {
                assert(n > 0);
                const self: *Self = @ptrCast(@alignCast(ctx));
                const underlying = self.getUnderlyingAllocatorPtr();
                const result = underlying.rawAlloc(n, log2_ptr_align, ret_addr) orelse
                    return null;
                assert(mem.isAlignedLog2(@intFromPtr(result), log2_ptr_align));
                return result;
            }

            pub fn resize(
                ctx: *anyopaque,
                buf: []u8,
                log2_buf_align: u8,
                new_len: usize,
                ret_addr: usize,
            ) bool {
                const self: *Self = @ptrCast(@alignCast(ctx));
                assert(buf.len > 0);
                const underlying = self.getUnderlyingAllocatorPtr();
                return underlying.rawResize(buf, log2_buf_align, new_len, ret_addr);
            }

            pub fn free(
                ctx: *anyopaque,
                buf: []u8,
                log2_buf_align: u8,
                ret_addr: usize,
            ) void {
                const self: *Self = @ptrCast(@alignCast(ctx));
                assert(buf.len > 0);
                const underlying = self.getUnderlyingAllocatorPtr();
                underlying.rawFree(buf, log2_buf_align, ret_addr);
            }

            pub fn reset(self: *Self) void {
                self.underlying_allocator.reset();
            }
        };
    }

    pub fn validationWrap(allocator: anytype) ValidationAllocator(@TypeOf(allocator)) {
        return ValidationAllocator(@TypeOf(allocator)).init(allocator);
    }

    /// An allocator helper function.  Adjusts an allocation length satisfy `len_align`.
    /// `full_len` should be the full capacity of the allocation which may be greater
    /// than the `len` that was requested.  This function should only be used by allocators
    /// that are unaffected by `len_align`.
    pub fn alignAllocLen(full_len: usize, alloc_len: usize, len_align: u29) usize {
        assert(alloc_len > 0);
        assert(alloc_len >= len_align);
        assert(full_len >= alloc_len);
        if (len_align == 0)
            return alloc_len;
        const adjusted = alignBackwardAnyAlign(full_len, len_align);
        assert(adjusted >= alloc_len);
        return adjusted;
    }

    const fail_allocator = Allocator{
        .ptr = undefined,
        .vtable = &failAllocator_vtable,
    };

    const failAllocator_vtable = Allocator.VTable{
        .alloc = failAllocatorAlloc,
        .resize = Allocator.noResize,
        .free = Allocator.noFree,
    };

    fn failAllocatorAlloc(_: *anyopaque, n: usize, log2_alignment: u8, ra: usize) ?[*]u8 {
        _ = n;
        _ = log2_alignment;
        _ = ra;
        return null;
    }

    test "Allocator basics" {
        try testing.expectError(error.OutOfMemory, fail_allocator.alloc(u8, 1));
        try testing.expectError(error.OutOfMemory, fail_allocator.allocSentinel(u8, 1, 0));
    }

    test "Allocator.resize" {
        const primitiveIntTypes = .{
            i8,
            u8,
            i16,
            u16,
            i32,
            u32,
            i64,
            u64,
            i128,
            u128,
            isize,
            usize,
        };
        inline for (primitiveIntTypes) |T| {
            var values = try testing.allocator.alloc(T, 100);
            defer testing.allocator.free(values);

            for (values, 0..) |*v, i| v.* = @as(T, @intCast(i));
            if (!testing.allocator.resize(values, values.len + 10)) return error.OutOfMemory;
            values = values.ptr[0 .. values.len + 10];
            try testing.expect(values.len == 110);
        }

        const primitiveFloatTypes = .{
            f16,
            f32,
            f64,
            f128,
        };
        inline for (primitiveFloatTypes) |T| {
            var values = try testing.allocator.alloc(T, 100);
            defer testing.allocator.free(values);

            for (values, 0..) |*v, i| v.* = @as(T, @floatFromInt(i));
            if (!testing.allocator.resize(values, values.len + 10)) return error.OutOfMemory;
            values = values.ptr[0 .. values.len + 10];
            try testing.expect(values.len == 110);
        }
    }

    /// Deprecated: use `@memcpy` if the arguments do not overlap, or
    /// `copyForwards` if they do.
    pub const copy = copyForwards;

    /// Copy all of source into dest at position 0.
    /// dest.len must be >= source.len.
    /// If the slices overlap, dest.ptr must be <= src.ptr.
    pub fn copyForwards(comptime T: type, dest: []T, source: []const T) void {
        for (dest[0..source.len], source) |*d, s| d.* = s;
    }

    /// Copy all of source into dest at position 0.
    /// dest.len must be >= source.len.
    /// If the slices overlap, dest.ptr must be >= src.ptr.
    pub fn copyBackwards(comptime T: type, dest: []T, source: []const T) void {
        // TODO instead of manually doing this check for the whole array

        // and turning off runtime safety, the compiler should detect loops like

        // this and automatically omit safety checks for loops

        @setRuntimeSafety(false);
        assert(dest.len >= source.len);
        var i = source.len;
        while (i > 0) {
            i -= 1;
            dest[i] = source[i];
        }
    }

    pub const set = @compileError("deprecated; use @memset instead");

    /// Generally, Zig users are encouraged to explicitly initialize all fields of a struct explicitly rather than using this function.
    /// However, it is recognized that there are sometimes use cases for initializing all fields to a "zero" value. For example, when
    /// interfacing with a C API where this practice is more common and relied upon. If you are performing code review and see this
    /// function used, examine closely - it may be a code smell.
    /// Zero initializes the type.
    /// This can be used to zero-initialize any type for which it makes sense. Structs will be initialized recursively.
    pub fn zeroes(comptime T: type) T {
        switch (@typeInfo(T)) {
            .ComptimeInt, .Int, .ComptimeFloat, .Float => {
                return @as(T, 0);
            },
            .Enum, .EnumLiteral => {
                return @as(T, @enumFromInt(0));
            },
            .Void => {
                return {};
            },
            .Bool => {
                return false;
            },
            .Optional, .Null => {
                return null;
            },
            .Struct => |struct_info| {
                if (@sizeOf(T) == 0) return undefined;
                if (struct_info.layout == .Extern) {
                    var item: T = undefined;
                    @memset(asBytes(&item), 0);
                    return item;
                } else {
                    var structure: T = undefined;
                    inline for (struct_info.fields) |field| {
                        if (!field.is_comptime) {
                            @field(structure, field.name) = zeroes(@TypeOf(@field(structure, field.name)));
                        }
                    }
                    return structure;
                }
            },
            .Pointer => |ptr_info| {
                switch (ptr_info.size) {
                    .Slice => {
                        if (ptr_info.sentinel) |sentinel| {
                            if (ptr_info.child == u8 and @as(*const u8, @ptrCast(sentinel)).* == 0) {
                                return ""; // A special case for the most common use-case: null-terminated strings.

                            }
                            @compileError("Can't set a sentinel slice to zero. This would require allocating memory.");
                        } else {
                            return &[_]ptr_info.child{};
                        }
                    },
                    .C => {
                        return null;
                    },
                    .One, .Many => {
                        if (ptr_info.is_allowzero) return @ptrFromInt(0);
                        @compileError("Only nullable and allowzero pointers can be set to zero.");
                    },
                }
            },
            .Array => |info| {
                if (info.sentinel) |sentinel_ptr| {
                    const sentinel = @as(*align(1) const info.child, @ptrCast(sentinel_ptr)).*;
                    return [_:sentinel]info.child{zeroes(info.child)} ** info.len;
                }
                return [_]info.child{zeroes(info.child)} ** info.len;
            },
            .Vector => |info| {
                return @splat(zeroes(info.child));
            },
            .Union => |info| {
                if (comptime meta.containerLayout(T) == .Extern) {
                    // The C language specification states that (global) unions

                    // should be zero initialized to the first named member.

                    return @unionInit(T, info.fields[0].name, zeroes(info.fields[0].type));
                }

                @compileError("Can't set a " ++ @typeName(T) ++ " to zero.");
            },
            .ErrorUnion,
            .ErrorSet,
            .Fn,
            .Type,
            .NoReturn,
            .Undefined,
            .Opaque,
            .Frame,
            .AnyFrame,
            => {
                @compileError("Can't set a " ++ @typeName(T) ++ " to zero.");
            },
        }
    }

    test "zeroes" {
        if (builtin.zig_backend == .stage2_llvm) {
            // Regressed in LLVM 14:

            // https://github.com/llvm/llvm-project/issues/55522

            return error.SkipZigTest;
        }

        const C_struct = extern struct {
            x: u32,
            y: u32,
        };

        var a = zeroes(C_struct);
        a.y += 10;

        try testing.expect(a.x == 0);
        try testing.expect(a.y == 10);

        const ZigStruct = struct {
            comptime comptime_field: u8 = 5,

            integral_types: struct {
                integer_0: i0,
                integer_8: i8,
                integer_16: i16,
                integer_32: i32,
                integer_64: i64,
                integer_128: i128,
                unsigned_0: u0,
                unsigned_8: u8,
                unsigned_16: u16,
                unsigned_32: u32,
                unsigned_64: u64,
                unsigned_128: u128,

                float_32: f32,
                float_64: f64,
            },

            pointers: struct {
                optional: ?*u8,
                c_pointer: [*c]u8,
                slice: []u8,
                nullTerminatedString: [:0]const u8,
            },

            array: [2]u32,
            vector_u32: @Vector(2, u32),
            vector_f32: @Vector(2, f32),
            vector_bool: @Vector(2, bool),
            optional_int: ?u8,
            empty: void,
            sentinel: [3:0]u8,
        };

        const b = zeroes(ZigStruct);
        try testing.expectEqual(@as(u8, 5), b.comptime_field);
        try testing.expectEqual(@as(i8, 0), b.integral_types.integer_0);
        try testing.expectEqual(@as(i8, 0), b.integral_types.integer_8);
        try testing.expectEqual(@as(i16, 0), b.integral_types.integer_16);
        try testing.expectEqual(@as(i32, 0), b.integral_types.integer_32);
        try testing.expectEqual(@as(i64, 0), b.integral_types.integer_64);
        try testing.expectEqual(@as(i128, 0), b.integral_types.integer_128);
        try testing.expectEqual(@as(u8, 0), b.integral_types.unsigned_0);
        try testing.expectEqual(@as(u8, 0), b.integral_types.unsigned_8);
        try testing.expectEqual(@as(u16, 0), b.integral_types.unsigned_16);
        try testing.expectEqual(@as(u32, 0), b.integral_types.unsigned_32);
        try testing.expectEqual(@as(u64, 0), b.integral_types.unsigned_64);
        try testing.expectEqual(@as(u128, 0), b.integral_types.unsigned_128);
        try testing.expectEqual(@as(f32, 0), b.integral_types.float_32);
        try testing.expectEqual(@as(f64, 0), b.integral_types.float_64);
        try testing.expectEqual(@as(?*u8, null), b.pointers.optional);
        try testing.expectEqual(@as([*c]u8, null), b.pointers.c_pointer);
        try testing.expectEqual(@as([]u8, &[_]u8{}), b.pointers.slice);
        try testing.expectEqual(@as([:0]const u8, ""), b.pointers.nullTerminatedString);
        for (b.array) |e| {
            try testing.expectEqual(@as(u32, 0), e);
        }
        try testing.expectEqual(@as(@TypeOf(b.vector_u32), @splat(0)), b.vector_u32);
        try testing.expectEqual(@as(@TypeOf(b.vector_f32), @splat(0.0)), b.vector_f32);
        try testing.expectEqual(@as(@TypeOf(b.vector_bool), @splat(false)), b.vector_bool);
        try testing.expectEqual(@as(?u8, null), b.optional_int);
        for (b.sentinel) |e| {
            try testing.expectEqual(@as(u8, 0), e);
        }

        const C_union = extern union {
            a: u8,
            b: u32,
        };

        var c = zeroes(C_union);
        try testing.expectEqual(@as(u8, 0), c.a);

        comptime var comptime_union = zeroes(C_union);
        try testing.expectEqual(@as(u8, 0), comptime_union.a);

        // Ensure zero sized struct with fields is initialized correctly.

        _ = zeroes(struct { handle: void });
    }

    /// Initializes all fields of the struct with their default value, or zero values if no default value is present.
    /// If the field is present in the provided initial values, it will have that value instead.
    /// Structs are initialized recursively.
    pub fn zeroInit(comptime T: type, init: anytype) T {
        const Init = @TypeOf(init);

        switch (@typeInfo(T)) {
            .Struct => |struct_info| {
                switch (@typeInfo(Init)) {
                    .Struct => |init_info| {
                        if (init_info.is_tuple) {
                            if (init_info.fields.len > struct_info.fields.len) {
                                @compileError("Tuple initializer has more elements than there are fields in `" ++ @typeName(T) ++ "`");
                            }
                        } else {
                            inline for (init_info.fields) |field| {
                                if (!@hasField(T, field.name)) {
                                    @compileError("Encountered an initializer for `" ++ field.name ++ "`, but it is not a field of " ++ @typeName(T));
                                }
                            }
                        }

                        var value: T = if (struct_info.layout == .Extern) zeroes(T) else undefined;

                        inline for (struct_info.fields, 0..) |field, i| {
                            if (field.is_comptime) {
                                continue;
                            }

                            if (init_info.is_tuple and init_info.fields.len > i) {
                                @field(value, field.name) = @field(init, init_info.fields[i].name);
                            } else if (@hasField(@TypeOf(init), field.name)) {
                                switch (@typeInfo(field.type)) {
                                    .Struct => {
                                        @field(value, field.name) = zeroInit(field.type, @field(init, field.name));
                                    },
                                    else => {
                                        @field(value, field.name) = @field(init, field.name);
                                    },
                                }
                            } else if (field.default_value) |default_value_ptr| {
                                const default_value = @as(*align(1) const field.type, @ptrCast(default_value_ptr)).*;
                                @field(value, field.name) = default_value;
                            } else {
                                switch (@typeInfo(field.type)) {
                                    .Struct => {
                                        @field(value, field.name) = std.mem.zeroInit(field.type, .{});
                                    },
                                    else => {
                                        @field(value, field.name) = std.mem.zeroes(@TypeOf(@field(value, field.name)));
                                    },
                                }
                            }
                        }

                        return value;
                    },
                    else => {
                        @compileError("The initializer must be a struct");
                    },
                }
            },
            else => {
                @compileError("Can't default init a " ++ @typeName(T));
            },
        }
    }

    test "zeroInit" {
        const I = struct {
            d: f64,
        };

        const S = struct {
            a: u32,
            b: ?bool,
            c: I,
            e: [3]u8,
            f: i64 = -1,
        };

        const s = zeroInit(S, .{
            .a = 42,
        });

        try testing.expectEqual(S{
            .a = 42,
            .b = null,
            .c = .{
                .d = 0,
            },
            .e = [3]u8{ 0, 0, 0 },
            .f = -1,
        }, s);

        const Color = struct {
            r: u8,
            g: u8,
            b: u8,
            a: u8,
        };

        const c = zeroInit(Color, .{ 255, 255 });
        try testing.expectEqual(Color{
            .r = 255,
            .g = 255,
            .b = 0,
            .a = 0,
        }, c);

        const Foo = struct {
            foo: u8 = 69,
            bar: u8,
        };

        const f = zeroInit(Foo, .{});
        try testing.expectEqual(Foo{
            .foo = 69,
            .bar = 0,
        }, f);

        const Bar = struct {
            foo: u32 = 666,
            bar: u32 = 420,
        };

        const b = zeroInit(Bar, .{69});
        try testing.expectEqual(Bar{
            .foo = 69,
            .bar = 420,
        }, b);

        const Baz = struct {
            foo: [:0]const u8 = "bar",
        };

        const baz1 = zeroInit(Baz, .{});
        try testing.expectEqual(Baz{}, baz1);

        const baz2 = zeroInit(Baz, .{ .foo = "zab" });
        try testing.expectEqualSlices(u8, "zab", baz2.foo);

        const NestedBaz = struct {
            bbb: Baz,
        };
        const nested_baz = zeroInit(NestedBaz, .{});
        try testing.expectEqual(NestedBaz{
            .bbb = Baz{},
        }, nested_baz);
    }

    pub fn sort(
        comptime T: type,
        items: []T,
        context: anytype,
        comptime lessThanFn: fn (@TypeOf(context), lhs: T, rhs: T) bool,
    ) void {
        std.sort.block(T, items, context, lessThanFn);
    }

    pub fn sortUnstable(
        comptime T: type,
        items: []T,
        context: anytype,
        comptime lessThanFn: fn (@TypeOf(context), lhs: T, rhs: T) bool,
    ) void {
        std.sort.pdq(T, items, context, lessThanFn);
    }

    /// TODO: currently this just calls `insertionSortContext`. The block sort implementation
    /// in this file needs to be adapted to use the sort context.
    pub fn sortContext(a: usize, b: usize, context: anytype) void {
        std.sort.insertionContext(a, b, context);
    }

    pub fn sortUnstableContext(a: usize, b: usize, context: anytype) void {
        std.sort.pdqContext(a, b, context);
    }

    /// Compares two slices of numbers lexicographically. O(n).
    pub fn order(comptime T: type, lhs: []const T, rhs: []const T) math.Order {
        const n = @min(lhs.len, rhs.len);
        for (lhs[0..n], rhs[0..n]) |lhs_elem, rhs_elem| {
            switch (math.order(lhs_elem, rhs_elem)) {
                .eq => continue,
                .lt => return .lt,
                .gt => return .gt,
            }
        }
        return math.order(lhs.len, rhs.len);
    }

    /// Compares two many-item pointers with NUL-termination lexicographically.
    pub fn orderZ(comptime T: type, lhs: [*:0]const T, rhs: [*:0]const T) math.Order {
        var i: usize = 0;
        while (lhs[i] == rhs[i] and lhs[i] != 0) : (i += 1) {}
        return math.order(lhs[i], rhs[i]);
    }

    test "order and orderZ" {
        try testing.expect(order(u8, "abcd", "bee") == .lt);
        try testing.expect(orderZ(u8, "abcd", "bee") == .lt);
        try testing.expect(order(u8, "abc", "abc") == .eq);
        try testing.expect(orderZ(u8, "abc", "abc") == .eq);
        try testing.expect(order(u8, "abc", "abc0") == .lt);
        try testing.expect(orderZ(u8, "abc", "abc0") == .lt);
        try testing.expect(order(u8, "", "") == .eq);
        try testing.expect(orderZ(u8, "", "") == .eq);
        try testing.expect(order(u8, "", "a") == .lt);
        try testing.expect(orderZ(u8, "", "a") == .lt);
    }

    /// Returns true if lhs < rhs, false otherwise
    pub fn lessThan(comptime T: type, lhs: []const T, rhs: []const T) bool {
        return order(T, lhs, rhs) == .lt;
    }

    test "lessThan" {
        try testing.expect(lessThan(u8, "abcd", "bee"));
        try testing.expect(!lessThan(u8, "abc", "abc"));
        try testing.expect(lessThan(u8, "abc", "abc0"));
        try testing.expect(!lessThan(u8, "", ""));
        try testing.expect(lessThan(u8, "", "a"));
    }

    /// Compares two slices and returns whether they are equal.
    pub fn eql(comptime T: type, a: []const T, b: []const T) bool {
        if (a.len != b.len) return false;
        if (a.ptr == b.ptr) return true;
        for (a, b) |a_elem, b_elem| {
            if (a_elem != b_elem) return false;
        }
        return true;
    }

    /// Compares two slices and returns the index of the first inequality.
    /// Returns null if the slices are equal.
    pub fn indexOfDiff(comptime T: type, a: []const T, b: []const T) ?usize {
        const shortest = @min(a.len, b.len);
        if (a.ptr == b.ptr)
            return if (a.len == b.len) null else shortest;
        var index: usize = 0;
        while (index < shortest) : (index += 1) if (a[index] != b[index]) return index;
        return if (a.len == b.len) null else shortest;
    }

    test "indexOfDiff" {
        try testing.expectEqual(indexOfDiff(u8, "one", "one"), null);
        try testing.expectEqual(indexOfDiff(u8, "one two", "one"), 3);
        try testing.expectEqual(indexOfDiff(u8, "one", "one two"), 3);
        try testing.expectEqual(indexOfDiff(u8, "one twx", "one two"), 6);
        try testing.expectEqual(indexOfDiff(u8, "xne", "one"), 0);
    }

    /// Takes a sentinel-terminated pointer and returns a slice preserving pointer attributes.
    /// `[*c]` pointers are assumed to be 0-terminated and assumed to not be allowzero.
    fn Span(comptime T: type) type {
        switch (@typeInfo(T)) {
            .Optional => |optional_info| {
                return ?Span(optional_info.child);
            },
            .Pointer => |ptr_info| {
                var new_ptr_info = ptr_info;
                switch (ptr_info.size) {
                    .C => {
                        new_ptr_info.sentinel = &@as(ptr_info.child, 0);
                        new_ptr_info.is_allowzero = false;
                    },
                    .Many => if (ptr_info.sentinel == null) @compileError("invalid type given to std.mem.span: " ++ @typeName(T)),
                    .One, .Slice => @compileError("invalid type given to std.mem.span: " ++ @typeName(T)),
                }
                new_ptr_info.size = .Slice;
                return @Type(.{ .Pointer = new_ptr_info });
            },
            else => {},
        }
        @compileError("invalid type given to std.mem.span: " ++ @typeName(T));
    }

    test "Span" {
        try testing.expect(Span([*:1]u16) == [:1]u16);
        try testing.expect(Span(?[*:1]u16) == ?[:1]u16);
        try testing.expect(Span([*:1]const u8) == [:1]const u8);
        try testing.expect(Span(?[*:1]const u8) == ?[:1]const u8);
        try testing.expect(Span([*c]u16) == [:0]u16);
        try testing.expect(Span(?[*c]u16) == ?[:0]u16);
        try testing.expect(Span([*c]const u8) == [:0]const u8);
        try testing.expect(Span(?[*c]const u8) == ?[:0]const u8);
    }

    /// Takes a sentinel-terminated pointer and returns a slice, iterating over the
    /// memory to find the sentinel and determine the length.
    /// Pointer attributes such as const are preserved.
    /// `[*c]` pointers are assumed to be non-null and 0-terminated.
    pub fn span(ptr: anytype) Span(@TypeOf(ptr)) {
        if (@typeInfo(@TypeOf(ptr)) == .Optional) {
            if (ptr) |non_null| {
                return span(non_null);
            } else {
                return null;
            }
        }
        const Result = Span(@TypeOf(ptr));
        const l = len(ptr);
        const ptr_info = @typeInfo(Result).Pointer;
        if (ptr_info.sentinel) |s_ptr| {
            const s = @as(*align(1) const ptr_info.child, @ptrCast(s_ptr)).*;
            return ptr[0..l :s];
        } else {
            return ptr[0..l];
        }
    }

    test "span" {
        var array: [5]u16 = [_]u16{ 1, 2, 3, 4, 5 };
        const ptr = @as([*:3]u16, array[0..2 :3]);
        try testing.expect(eql(u16, span(ptr), &[_]u16{ 1, 2 }));
        try testing.expectEqual(@as(?[:0]u16, null), span(@as(?[*:0]u16, null)));
    }

    /// Helper for the return type of sliceTo()
    fn SliceTo(comptime T: type, comptime end: meta.Elem(T)) type {
        switch (@typeInfo(T)) {
            .Optional => |optional_info| {
                return ?SliceTo(optional_info.child, end);
            },
            .Pointer => |ptr_info| {
                var new_ptr_info = ptr_info;
                new_ptr_info.size = .Slice;
                switch (ptr_info.size) {
                    .One => switch (@typeInfo(ptr_info.child)) {
                        .Array => |array_info| {
                            new_ptr_info.child = array_info.child;
                            // The return type must only be sentinel terminated if we are guaranteed

                            // to find the value searched for, which is only the case if it matches

                            // the sentinel of the type passed.

                            if (array_info.sentinel) |sentinel_ptr| {
                                const sentinel = @as(*align(1) const array_info.child, @ptrCast(sentinel_ptr)).*;
                                if (end == sentinel) {
                                    new_ptr_info.sentinel = &end;
                                } else {
                                    new_ptr_info.sentinel = null;
                                }
                            }
                        },
                        else => {},
                    },
                    .Many, .Slice => {
                        // The return type must only be sentinel terminated if we are guaranteed

                        // to find the value searched for, which is only the case if it matches

                        // the sentinel of the type passed.

                        if (ptr_info.sentinel) |sentinel_ptr| {
                            const sentinel = @as(*align(1) const ptr_info.child, @ptrCast(sentinel_ptr)).*;
                            if (end == sentinel) {
                                new_ptr_info.sentinel = &end;
                            } else {
                                new_ptr_info.sentinel = null;
                            }
                        }
                    },
                    .C => {
                        new_ptr_info.sentinel = &end;
                        // C pointers are always allowzero, but we don't want the return type to be.

                        assert(new_ptr_info.is_allowzero);
                        new_ptr_info.is_allowzero = false;
                    },
                }
                return @Type(.{ .Pointer = new_ptr_info });
            },
            else => {},
        }
        @compileError("invalid type given to std.mem.sliceTo: " ++ @typeName(T));
    }

    /// Takes an array, a pointer to an array, a sentinel-terminated pointer, or a slice and
    /// iterates searching for the first occurrence of `end`, returning the scanned slice.
    /// If `end` is not found, the full length of the array/slice/sentinel terminated pointer is returned.
    /// If the pointer type is sentinel terminated and `end` matches that terminator, the
    /// resulting slice is also sentinel terminated.
    /// Pointer properties such as mutability and alignment are preserved.
    /// C pointers are assumed to be non-null.
    pub fn sliceTo(ptr: anytype, comptime end: meta.Elem(@TypeOf(ptr))) SliceTo(@TypeOf(ptr), end) {
        if (@typeInfo(@TypeOf(ptr)) == .Optional) {
            const non_null = ptr orelse return null;
            return sliceTo(non_null, end);
        }
        const Result = SliceTo(@TypeOf(ptr), end);
        const length = lenSliceTo(ptr, end);
        const ptr_info = @typeInfo(Result).Pointer;
        if (ptr_info.sentinel) |s_ptr| {
            const s = @as(*align(1) const ptr_info.child, @ptrCast(s_ptr)).*;
            return ptr[0..length :s];
        } else {
            return ptr[0..length];
        }
    }

    test "sliceTo" {
        try testing.expectEqualSlices(u8, "aoeu", sliceTo("aoeu", 0));

        {
            var array: [5]u16 = [_]u16{ 1, 2, 3, 4, 5 };
            try testing.expectEqualSlices(u16, &array, sliceTo(&array, 0));
            try testing.expectEqualSlices(u16, array[0..3], sliceTo(array[0..3], 0));
            try testing.expectEqualSlices(u16, array[0..2], sliceTo(&array, 3));
            try testing.expectEqualSlices(u16, array[0..2], sliceTo(array[0..3], 3));

            const sentinel_ptr = @as([*:5]u16, @ptrCast(&array));
            try testing.expectEqualSlices(u16, array[0..2], sliceTo(sentinel_ptr, 3));
            try testing.expectEqualSlices(u16, array[0..4], sliceTo(sentinel_ptr, 99));

            const optional_sentinel_ptr = @as(?[*:5]u16, @ptrCast(&array));
            try testing.expectEqualSlices(u16, array[0..2], sliceTo(optional_sentinel_ptr, 3).?);
            try testing.expectEqualSlices(u16, array[0..4], sliceTo(optional_sentinel_ptr, 99).?);

            const c_ptr = @as([*c]u16, &array);
            try testing.expectEqualSlices(u16, array[0..2], sliceTo(c_ptr, 3));

            const slice: []u16 = &array;
            try testing.expectEqualSlices(u16, array[0..2], sliceTo(slice, 3));
            try testing.expectEqualSlices(u16, &array, sliceTo(slice, 99));

            const sentinel_slice: [:5]u16 = array[0..4 :5];
            try testing.expectEqualSlices(u16, array[0..2], sliceTo(sentinel_slice, 3));
            try testing.expectEqualSlices(u16, array[0..4], sliceTo(sentinel_slice, 99));
        }
        {
            var sentinel_array: [5:0]u16 = [_:0]u16{ 1, 2, 3, 4, 5 };
            try testing.expectEqualSlices(u16, sentinel_array[0..2], sliceTo(&sentinel_array, 3));
            try testing.expectEqualSlices(u16, &sentinel_array, sliceTo(&sentinel_array, 0));
            try testing.expectEqualSlices(u16, &sentinel_array, sliceTo(&sentinel_array, 99));
        }

        try testing.expectEqual(@as(?[]u8, null), sliceTo(@as(?[]u8, null), 0));
    }

    /// Private helper for sliceTo(). If you want the length, use sliceTo(foo, x).len
    fn lenSliceTo(ptr: anytype, comptime end: meta.Elem(@TypeOf(ptr))) usize {
        switch (@typeInfo(@TypeOf(ptr))) {
            .Pointer => |ptr_info| switch (ptr_info.size) {
                .One => switch (@typeInfo(ptr_info.child)) {
                    .Array => |array_info| {
                        if (array_info.sentinel) |sentinel_ptr| {
                            const sentinel = @as(*align(1) const array_info.child, @ptrCast(sentinel_ptr)).*;
                            if (sentinel == end) {
                                return indexOfSentinel(array_info.child, end, ptr);
                            }
                        }
                        return indexOfScalar(array_info.child, ptr, end) orelse array_info.len;
                    },
                    else => {},
                },
                .Many => if (ptr_info.sentinel) |sentinel_ptr| {
                    const sentinel = @as(*align(1) const ptr_info.child, @ptrCast(sentinel_ptr)).*;
                    // We may be looking for something other than the sentinel,

                    // but iterating past the sentinel would be a bug so we need

                    // to check for both.

                    var i: usize = 0;
                    while (ptr[i] != end and ptr[i] != sentinel) i += 1;
                    return i;
                },
                .C => {
                    assert(ptr != null);
                    return indexOfSentinel(ptr_info.child, end, ptr);
                },
                .Slice => {
                    if (ptr_info.sentinel) |sentinel_ptr| {
                        const sentinel = @as(*align(1) const ptr_info.child, @ptrCast(sentinel_ptr)).*;
                        if (sentinel == end) {
                            return indexOfSentinel(ptr_info.child, sentinel, ptr);
                        }
                    }
                    return indexOfScalar(ptr_info.child, ptr, end) orelse ptr.len;
                },
            },
            else => {},
        }
        @compileError("invalid type given to std.mem.sliceTo: " ++ @typeName(@TypeOf(ptr)));
    }

    test "lenSliceTo" {
        try testing.expect(lenSliceTo("aoeu", 0) == 4);

        {
            var array: [5]u16 = [_]u16{ 1, 2, 3, 4, 5 };
            try testing.expectEqual(@as(usize, 5), lenSliceTo(&array, 0));
            try testing.expectEqual(@as(usize, 3), lenSliceTo(array[0..3], 0));
            try testing.expectEqual(@as(usize, 2), lenSliceTo(&array, 3));
            try testing.expectEqual(@as(usize, 2), lenSliceTo(array[0..3], 3));

            const sentinel_ptr = @as([*:5]u16, @ptrCast(&array));
            try testing.expectEqual(@as(usize, 2), lenSliceTo(sentinel_ptr, 3));
            try testing.expectEqual(@as(usize, 4), lenSliceTo(sentinel_ptr, 99));

            const c_ptr = @as([*c]u16, &array);
            try testing.expectEqual(@as(usize, 2), lenSliceTo(c_ptr, 3));

            const slice: []u16 = &array;
            try testing.expectEqual(@as(usize, 2), lenSliceTo(slice, 3));
            try testing.expectEqual(@as(usize, 5), lenSliceTo(slice, 99));

            const sentinel_slice: [:5]u16 = array[0..4 :5];
            try testing.expectEqual(@as(usize, 2), lenSliceTo(sentinel_slice, 3));
            try testing.expectEqual(@as(usize, 4), lenSliceTo(sentinel_slice, 99));
        }
        {
            var sentinel_array: [5:0]u16 = [_:0]u16{ 1, 2, 3, 4, 5 };
            try testing.expectEqual(@as(usize, 2), lenSliceTo(&sentinel_array, 3));
            try testing.expectEqual(@as(usize, 5), lenSliceTo(&sentinel_array, 0));
            try testing.expectEqual(@as(usize, 5), lenSliceTo(&sentinel_array, 99));
        }
    }

    /// Takes a sentinel-terminated pointer and iterates over the memory to find the
    /// sentinel and determine the length.
    /// `[*c]` pointers are assumed to be non-null and 0-terminated.
    pub fn len(value: anytype) usize {
        switch (@typeInfo(@TypeOf(value))) {
            .Pointer => |info| switch (info.size) {
                .Many => {
                    const sentinel_ptr = info.sentinel orelse
                        @compileError("invalid type given to std.mem.len: " ++ @typeName(@TypeOf(value)));
                    const sentinel = @as(*align(1) const info.child, @ptrCast(sentinel_ptr)).*;
                    return indexOfSentinel(info.child, sentinel, value);
                },
                .C => {
                    assert(value != null);
                    return indexOfSentinel(info.child, 0, value);
                },
                else => @compileError("invalid type given to std.mem.len: " ++ @typeName(@TypeOf(value))),
            },
            else => @compileError("invalid type given to std.mem.len: " ++ @typeName(@TypeOf(value))),
        }
    }

    test "len" {
        var array: [5]u16 = [_]u16{ 1, 2, 0, 4, 5 };
        const ptr = @as([*:4]u16, array[0..3 :4]);
        try testing.expect(len(ptr) == 3);
        const c_ptr = @as([*c]u16, ptr);
        try testing.expect(len(c_ptr) == 2);
    }

    pub fn indexOfSentinel(comptime Elem: type, comptime sentinel: Elem, ptr: [*:sentinel]const Elem) usize {
        var i: usize = 0;
        while (ptr[i] != sentinel) {
            i += 1;
        }
        return i;
    }

    /// Returns true if all elements in a slice are equal to the scalar value provided
    pub fn allEqual(comptime T: type, slice: []const T, scalar: T) bool {
        for (slice) |item| {
            if (item != scalar) return false;
        }
        return true;
    }

    /// Remove a set of values from the beginning of a slice.
    pub fn trimLeft(comptime T: type, slice: []const T, values_to_strip: []const T) []const T {
        var begin: usize = 0;
        while (begin < slice.len and indexOfScalar(T, values_to_strip, slice[begin]) != null) : (begin += 1) {}
        return slice[begin..];
    }

    /// Remove a set of values from the end of a slice.
    pub fn trimRight(comptime T: type, slice: []const T, values_to_strip: []const T) []const T {
        var end: usize = slice.len;
        while (end > 0 and indexOfScalar(T, values_to_strip, slice[end - 1]) != null) : (end -= 1) {}
        return slice[0..end];
    }

    /// Remove a set of values from the beginning and end of a slice.
    pub fn trim(comptime T: type, slice: []const T, values_to_strip: []const T) []const T {
        var begin: usize = 0;
        var end: usize = slice.len;
        while (begin < end and indexOfScalar(T, values_to_strip, slice[begin]) != null) : (begin += 1) {}
        while (end > begin and indexOfScalar(T, values_to_strip, slice[end - 1]) != null) : (end -= 1) {}
        return slice[begin..end];
    }

    test "trim" {
        try testing.expectEqualSlices(u8, "foo\n ", trimLeft(u8, " foo\n ", " \n"));
        try testing.expectEqualSlices(u8, " foo", trimRight(u8, " foo\n ", " \n"));
        try testing.expectEqualSlices(u8, "foo", trim(u8, " foo\n ", " \n"));
        try testing.expectEqualSlices(u8, "foo", trim(u8, "foo", " \n"));
    }

    /// Linear search for the index of a scalar value inside a slice.
    pub fn indexOfScalar(comptime T: type, slice: []const T, value: T) ?usize {
        return indexOfScalarPos(T, slice, 0, value);
    }

    /// Linear search for the last index of a scalar value inside a slice.
    pub fn lastIndexOfScalar(comptime T: type, slice: []const T, value: T) ?usize {
        var i: usize = slice.len;
        while (i != 0) {
            i -= 1;
            if (slice[i] == value) return i;
        }
        return null;
    }

    pub fn indexOfScalarPos(comptime T: type, slice: []const T, start_index: usize, value: T) ?usize {
        var i: usize = start_index;
        while (i < slice.len) : (i += 1) {
            if (slice[i] == value) return i;
        }
        return null;
    }

    pub fn indexOfAny(comptime T: type, slice: []const T, values: []const T) ?usize {
        return indexOfAnyPos(T, slice, 0, values);
    }

    pub fn lastIndexOfAny(comptime T: type, slice: []const T, values: []const T) ?usize {
        var i: usize = slice.len;
        while (i != 0) {
            i -= 1;
            for (values) |value| {
                if (slice[i] == value) return i;
            }
        }
        return null;
    }

    pub fn indexOfAnyPos(comptime T: type, slice: []const T, start_index: usize, values: []const T) ?usize {
        var i: usize = start_index;
        while (i < slice.len) : (i += 1) {
            for (values) |value| {
                if (slice[i] == value) return i;
            }
        }
        return null;
    }

    /// Find the first item in `slice` which is not contained in `values`.
    ///
    /// Comparable to `strspn` in the C standard library.
    pub fn indexOfNone(comptime T: type, slice: []const T, values: []const T) ?usize {
        return indexOfNonePos(T, slice, 0, values);
    }

    /// Find the last item in `slice` which is not contained in `values`.
    ///
    /// Like `strspn` in the C standard library, but searches from the end.
    pub fn lastIndexOfNone(comptime T: type, slice: []const T, values: []const T) ?usize {
        var i: usize = slice.len;
        outer: while (i != 0) {
            i -= 1;
            for (values) |value| {
                if (slice[i] == value) continue :outer;
            }
            return i;
        }
        return null;
    }

    /// Find the first item in `slice[start_index..]` which is not contained in `values`.
    /// The returned index will be relative to the start of `slice`, and never less than `start_index`.
    ///
    /// Comparable to `strspn` in the C standard library.
    pub fn indexOfNonePos(comptime T: type, slice: []const T, start_index: usize, values: []const T) ?usize {
        var i: usize = start_index;
        outer: while (i < slice.len) : (i += 1) {
            for (values) |value| {
                if (slice[i] == value) continue :outer;
            }
            return i;
        }
        return null;
    }

    test "indexOfNone" {
        try testing.expect(indexOfNone(u8, "abc123", "123").? == 0);
        try testing.expect(lastIndexOfNone(u8, "abc123", "123").? == 2);
        try testing.expect(indexOfNone(u8, "123abc", "123").? == 3);
        try testing.expect(lastIndexOfNone(u8, "123abc", "123").? == 5);
        try testing.expect(indexOfNone(u8, "123123", "123") == null);
        try testing.expect(indexOfNone(u8, "333333", "123") == null);

        try testing.expect(indexOfNonePos(u8, "abc123", 3, "321") == null);
    }

    pub fn indexOf(comptime T: type, haystack: []const T, needle: []const T) ?usize {
        return indexOfPos(T, haystack, 0, needle);
    }

    /// Find the index in a slice of a sub-slice, searching from the end backwards.
    /// To start looking at a different index, slice the haystack first.
    /// Consider using `lastIndexOf` instead of this, which will automatically use a
    /// more sophisticated algorithm on larger inputs.
    pub fn lastIndexOfLinear(comptime T: type, haystack: []const T, needle: []const T) ?usize {
        var i: usize = haystack.len - needle.len;
        while (true) : (i -= 1) {
            if (mem.eql(T, haystack[i .. i + needle.len], needle)) return i;
            if (i == 0) return null;
        }
    }

    /// Consider using `indexOfPos` instead of this, which will automatically use a
    /// more sophisticated algorithm on larger inputs.
    pub fn indexOfPosLinear(comptime T: type, haystack: []const T, start_index: usize, needle: []const T) ?usize {
        var i: usize = start_index;
        const end = haystack.len - needle.len;
        while (i <= end) : (i += 1) {
            if (eql(T, haystack[i .. i + needle.len], needle)) return i;
        }
        return null;
    }

    fn boyerMooreHorspoolPreprocessReverse(pattern: []const u8, table: *[256]usize) void {
        for (table) |*c| {
            c.* = pattern.len;
        }

        var i: usize = pattern.len - 1;
        // The first item is intentionally ignored and the skip size will be pattern.len.

        // This is the standard way Boyer-Moore-Horspool is implemented.

        while (i > 0) : (i -= 1) {
            table[pattern[i]] = i;
        }
    }

    fn boyerMooreHorspoolPreprocess(pattern: []const u8, table: *[256]usize) void {
        for (table) |*c| {
            c.* = pattern.len;
        }

        var i: usize = 0;
        // The last item is intentionally ignored and the skip size will be pattern.len.

        // This is the standard way Boyer-Moore-Horspool is implemented.

        while (i < pattern.len - 1) : (i += 1) {
            table[pattern[i]] = pattern.len - 1 - i;
        }
    }

    /// Find the index in a slice of a sub-slice, searching from the end backwards.
    /// To start looking at a different index, slice the haystack first.
    /// Uses the Reverse Boyer-Moore-Horspool algorithm on large inputs;
    /// `lastIndexOfLinear` on small inputs.
    pub fn lastIndexOf(comptime T: type, haystack: []const T, needle: []const T) ?usize {
        if (needle.len > haystack.len) return null;
        if (needle.len == 0) return haystack.len;

        if (!meta.trait.hasUniqueRepresentation(T) or haystack.len < 52 or needle.len <= 4)
            return lastIndexOfLinear(T, haystack, needle);

        const haystack_bytes = sliceAsBytes(haystack);
        const needle_bytes = sliceAsBytes(needle);

        var skip_table: [256]usize = undefined;
        boyerMooreHorspoolPreprocessReverse(needle_bytes, skip_table[0..]);

        var i: usize = haystack_bytes.len - needle_bytes.len;
        while (true) {
            if (i % @sizeOf(T) == 0 and mem.eql(u8, haystack_bytes[i .. i + needle_bytes.len], needle_bytes)) {
                return @divExact(i, @sizeOf(T));
            }
            const skip = skip_table[haystack_bytes[i]];
            if (skip > i) break;
            i -= skip;
        }

        return null;
    }

    /// Uses Boyer-Moore-Horspool algorithm on large inputs; `indexOfPosLinear` on small inputs.
    pub fn indexOfPos(comptime T: type, haystack: []const T, start_index: usize, needle: []const T) ?usize {
        if (needle.len > haystack.len) return null;
        if (needle.len == 0) return start_index;

        if (!meta.trait.hasUniqueRepresentation(T) or haystack.len < 52 or needle.len <= 4)
            return indexOfPosLinear(T, haystack, start_index, needle);

        const haystack_bytes = sliceAsBytes(haystack);
        const needle_bytes = sliceAsBytes(needle);

        var skip_table: [256]usize = undefined;
        boyerMooreHorspoolPreprocess(needle_bytes, skip_table[0..]);

        var i: usize = start_index * @sizeOf(T);
        while (i <= haystack_bytes.len - needle_bytes.len) {
            if (i % @sizeOf(T) == 0 and mem.eql(u8, haystack_bytes[i .. i + needle_bytes.len], needle_bytes)) {
                return @divExact(i, @sizeOf(T));
            }
            i += skip_table[haystack_bytes[i + needle_bytes.len - 1]];
        }

        return null;
    }

    test "indexOf" {
        try testing.expect(indexOf(u8, "one two three four five six seven eight nine ten eleven", "three four").? == 8);
        try testing.expect(lastIndexOf(u8, "one two three four five six seven eight nine ten eleven", "three four").? == 8);
        try testing.expect(indexOf(u8, "one two three four five six seven eight nine ten eleven", "two two") == null);
        try testing.expect(lastIndexOf(u8, "one two three four five six seven eight nine ten eleven", "two two") == null);

        try testing.expect(indexOf(u8, "one two three four five six seven eight nine ten", "").? == 0);
        try testing.expect(lastIndexOf(u8, "one two three four five six seven eight nine ten", "").? == 48);

        try testing.expect(indexOf(u8, "one two three four", "four").? == 14);
        try testing.expect(lastIndexOf(u8, "one two three two four", "two").? == 14);
        try testing.expect(indexOf(u8, "one two three four", "gour") == null);
        try testing.expect(lastIndexOf(u8, "one two three four", "gour") == null);
        try testing.expect(indexOf(u8, "foo", "foo").? == 0);
        try testing.expect(lastIndexOf(u8, "foo", "foo").? == 0);
        try testing.expect(indexOf(u8, "foo", "fool") == null);
        try testing.expect(lastIndexOf(u8, "foo", "lfoo") == null);
        try testing.expect(lastIndexOf(u8, "foo", "fool") == null);

        try testing.expect(indexOf(u8, "foo foo", "foo").? == 0);
        try testing.expect(lastIndexOf(u8, "foo foo", "foo").? == 4);
        try testing.expect(lastIndexOfAny(u8, "boo, cat", "abo").? == 6);
        try testing.expect(lastIndexOfScalar(u8, "boo", 'o').? == 2);
    }

    test "indexOf multibyte" {
        {
            // make haystack and needle long enough to trigger Boyer-Moore-Horspool algorithm

            const haystack = [1]u16{0} ** 100 ++ [_]u16{ 0xbbaa, 0xccbb, 0xddcc, 0xeedd, 0xffee, 0x00ff };
            const needle = [_]u16{ 0xbbaa, 0xccbb, 0xddcc, 0xeedd, 0xffee };
            try testing.expectEqual(indexOfPos(u16, &haystack, 0, &needle), 100);

            // check for misaligned false positives (little and big endian)

            const needleLE = [_]u16{ 0xbbbb, 0xcccc, 0xdddd, 0xeeee, 0xffff };
            try testing.expectEqual(indexOfPos(u16, &haystack, 0, &needleLE), null);
            const needleBE = [_]u16{ 0xaacc, 0xbbdd, 0xccee, 0xddff, 0xee00 };
            try testing.expectEqual(indexOfPos(u16, &haystack, 0, &needleBE), null);
        }

        {
            // make haystack and needle long enough to trigger Boyer-Moore-Horspool algorithm

            const haystack = [_]u16{ 0xbbaa, 0xccbb, 0xddcc, 0xeedd, 0xffee, 0x00ff } ++ [1]u16{0} ** 100;
            const needle = [_]u16{ 0xbbaa, 0xccbb, 0xddcc, 0xeedd, 0xffee };
            try testing.expectEqual(lastIndexOf(u16, &haystack, &needle), 0);

            // check for misaligned false positives (little and big endian)

            const needleLE = [_]u16{ 0xbbbb, 0xcccc, 0xdddd, 0xeeee, 0xffff };
            try testing.expectEqual(lastIndexOf(u16, &haystack, &needleLE), null);
            const needleBE = [_]u16{ 0xaacc, 0xbbdd, 0xccee, 0xddff, 0xee00 };
            try testing.expectEqual(lastIndexOf(u16, &haystack, &needleBE), null);
        }
    }

    test "indexOfPos empty needle" {
        try testing.expectEqual(indexOfPos(u8, "abracadabra", 5, ""), 5);
    }

    /// Returns the number of needles inside the haystack
    /// needle.len must be > 0
    /// does not count overlapping needles
    pub fn count(comptime T: type, haystack: []const T, needle: []const T) usize {
        assert(needle.len > 0);
        var i: usize = 0;
        var found: usize = 0;

        while (indexOfPos(T, haystack, i, needle)) |idx| {
            i = idx + needle.len;
            found += 1;
        }

        return found;
    }

    test "count" {
        try testing.expect(count(u8, "", "h") == 0);
        try testing.expect(count(u8, "h", "h") == 1);
        try testing.expect(count(u8, "hh", "h") == 2);
        try testing.expect(count(u8, "world!", "hello") == 0);
        try testing.expect(count(u8, "hello world!", "hello") == 1);
        try testing.expect(count(u8, "   abcabc   abc", "abc") == 3);
        try testing.expect(count(u8, "udexdcbvbruhasdrw", "bruh") == 1);
        try testing.expect(count(u8, "foo bar", "o bar") == 1);
        try testing.expect(count(u8, "foofoofoo", "foo") == 3);
        try testing.expect(count(u8, "fffffff", "ff") == 3);
        try testing.expect(count(u8, "owowowu", "owowu") == 1);
    }

    /// Returns true if the haystack contains expected_count or more needles
    /// needle.len must be > 0
    /// does not count overlapping needles
    pub fn containsAtLeast(comptime T: type, haystack: []const T, expected_count: usize, needle: []const T) bool {
        assert(needle.len > 0);
        if (expected_count == 0) return true;

        var i: usize = 0;
        var found: usize = 0;

        while (indexOfPos(T, haystack, i, needle)) |idx| {
            i = idx + needle.len;
            found += 1;
            if (found == expected_count) return true;
        }
        return false;
    }

    test "containsAtLeast" {
        try testing.expect(containsAtLeast(u8, "aa", 0, "a"));
        try testing.expect(containsAtLeast(u8, "aa", 1, "a"));
        try testing.expect(containsAtLeast(u8, "aa", 2, "a"));
        try testing.expect(!containsAtLeast(u8, "aa", 3, "a"));

        try testing.expect(containsAtLeast(u8, "radaradar", 1, "radar"));
        try testing.expect(!containsAtLeast(u8, "radaradar", 2, "radar"));

        try testing.expect(containsAtLeast(u8, "radarradaradarradar", 3, "radar"));
        try testing.expect(!containsAtLeast(u8, "radarradaradarradar", 4, "radar"));

        try testing.expect(containsAtLeast(u8, "   radar      radar   ", 2, "radar"));
        try testing.expect(!containsAtLeast(u8, "   radar      radar   ", 3, "radar"));
    }

    /// Reads an integer from memory with size equal to bytes.len.
    /// T specifies the return type, which must be large enough to store
    /// the result.
    pub fn readVarInt(comptime ReturnType: type, bytes: []const u8, endian: Endian) ReturnType {
        var result: ReturnType = 0;
        switch (endian) {
            .Big => {
                for (bytes) |b| {
                    result = (result << 8) | b;
                }
            },
            .Little => {
                const ShiftType = math.Log2Int(ReturnType);
                for (bytes, 0..) |b, index| {
                    result = result | (@as(ReturnType, b) << @as(ShiftType, @intCast(index * 8)));
                }
            },
        }
        return result;
    }

    /// Loads an integer from packed memory with provided bit_count, bit_offset, and signedness.
    /// Asserts that T is large enough to store the read value.
    ///
    /// Example:
    ///     const T = packed struct(u16){ a: u3, b: u7, c: u6 };
    ///     var st = T{ .a = 1, .b = 2, .c = 4 };
    ///     const b_field = readVarPackedInt(u64, std.mem.asBytes(&st), @bitOffsetOf(T, "b"), 7, builtin.cpu.arch.endian(), .unsigned);
    ///
    pub fn readVarPackedInt(
        comptime T: type,
        bytes: []const u8,
        bit_offset: usize,
        bit_count: usize,
        endian: std.builtin.Endian,
        signedness: std.builtin.Signedness,
    ) T {
        const uN = std.meta.Int(.unsigned, @bitSizeOf(T));
        const iN = std.meta.Int(.signed, @bitSizeOf(T));
        const Log2N = std.math.Log2Int(T);

        const read_size = (bit_count + (bit_offset % 8) + 7) / 8;
        const bit_shift = @as(u3, @intCast(bit_offset % 8));
        const pad = @as(Log2N, @intCast(@bitSizeOf(T) - bit_count));

        const lowest_byte = switch (endian) {
            .Big => bytes.len - (bit_offset / 8) - read_size,
            .Little => bit_offset / 8,
        };
        const read_bytes = bytes[lowest_byte..][0..read_size];

        if (@bitSizeOf(T) <= 8) {
            // These are the same shifts/masks we perform below, but adds `@truncate`/`@intCast`

            // where needed since int is smaller than a byte.

            const value = if (read_size == 1) b: {
                break :b @as(uN, @truncate(read_bytes[0] >> bit_shift));
            } else b: {
                const i: u1 = @intFromBool(endian == .Big);
                const head = @as(uN, @truncate(read_bytes[i] >> bit_shift));
                const tail_shift = @as(Log2N, @intCast(@as(u4, 8) - bit_shift));
                const tail = @as(uN, @truncate(read_bytes[1 - i]));
                break :b (tail << tail_shift) | head;
            };
            switch (signedness) {
                .signed => return @as(T, @intCast((@as(iN, @bitCast(value)) << pad) >> pad)),
                .unsigned => return @as(T, @intCast((@as(uN, @bitCast(value)) << pad) >> pad)),
            }
        }

        // Copy the value out (respecting endianness), accounting for bit_shift

        var int: uN = 0;
        switch (endian) {
            .Big => {
                for (read_bytes[0 .. read_size - 1]) |elem| {
                    int = elem | (int << 8);
                }
                int = (read_bytes[read_size - 1] >> bit_shift) | (int << (@as(u4, 8) - bit_shift));
            },
            .Little => {
                int = read_bytes[0] >> bit_shift;
                for (read_bytes[1..], 0..) |elem, i| {
                    int |= (@as(uN, elem) << @as(Log2N, @intCast((8 * (i + 1) - bit_shift))));
                }
            },
        }
        switch (signedness) {
            .signed => return @as(T, @intCast((@as(iN, @bitCast(int)) << pad) >> pad)),
            .unsigned => return @as(T, @intCast((@as(uN, @bitCast(int)) << pad) >> pad)),
        }
    }

    /// Reads an integer from memory with bit count specified by T.
    /// The bit count of T must be evenly divisible by 8.
    /// This function cannot fail and cannot cause undefined behavior.
    /// Assumes the endianness of memory is native. This means the function can
    /// simply pointer cast memory.
    pub fn readIntNative(comptime T: type, bytes: *const [@divExact(@typeInfo(T).Int.bits, 8)]u8) T {
        return @as(*align(1) const T, @ptrCast(bytes)).*;
    }

    /// Reads an integer from memory with bit count specified by T.
    /// The bit count of T must be evenly divisible by 8.
    /// This function cannot fail and cannot cause undefined behavior.
    /// Assumes the endianness of memory is foreign, so it must byte-swap.
    pub fn readIntForeign(comptime T: type, bytes: *const [@divExact(@typeInfo(T).Int.bits, 8)]u8) T {
        return @byteSwap(readIntNative(T, bytes));
    }

    pub const readIntLittle = switch (native_endian) {
        .Little => readIntNative,
        .Big => readIntForeign,
    };

    pub const readIntBig = switch (native_endian) {
        .Little => readIntForeign,
        .Big => readIntNative,
    };

    /// Asserts that bytes.len >= @typeInfo(T).Int.bits / 8. Reads the integer starting from index 0
    /// and ignores extra bytes.
    /// The bit count of T must be evenly divisible by 8.
    /// Assumes the endianness of memory is native. This means the function can
    /// simply pointer cast memory.
    pub fn readIntSliceNative(comptime T: type, bytes: []const u8) T {
        const n = @divExact(@typeInfo(T).Int.bits, 8);
        assert(bytes.len >= n);
        return readIntNative(T, bytes[0..n]);
    }

    /// Asserts that bytes.len >= @typeInfo(T).Int.bits / 8. Reads the integer starting from index 0
    /// and ignores extra bytes.
    /// The bit count of T must be evenly divisible by 8.
    /// Assumes the endianness of memory is foreign, so it must byte-swap.
    pub fn readIntSliceForeign(comptime T: type, bytes: []const u8) T {
        return @byteSwap(readIntSliceNative(T, bytes));
    }

    pub const readIntSliceLittle = switch (native_endian) {
        .Little => readIntSliceNative,
        .Big => readIntSliceForeign,
    };

    pub const readIntSliceBig = switch (native_endian) {
        .Little => readIntSliceForeign,
        .Big => readIntSliceNative,
    };

    /// Reads an integer from memory with bit count specified by T.
    /// The bit count of T must be evenly divisible by 8.
    /// This function cannot fail and cannot cause undefined behavior.
    pub fn readInt(comptime T: type, bytes: *const [@divExact(@typeInfo(T).Int.bits, 8)]u8, endian: Endian) T {
        if (endian == native_endian) {
            return readIntNative(T, bytes);
        } else {
            return readIntForeign(T, bytes);
        }
    }

    fn readPackedIntLittle(comptime T: type, bytes: []const u8, bit_offset: usize) T {
        const uN = std.meta.Int(.unsigned, @bitSizeOf(T));
        const Log2N = std.math.Log2Int(T);

        const bit_count = @as(usize, @bitSizeOf(T));
        const bit_shift = @as(u3, @intCast(bit_offset % 8));

        const load_size = (bit_count + 7) / 8;
        const load_tail_bits = @as(u3, @intCast((load_size * 8) - bit_count));
        const LoadInt = std.meta.Int(.unsigned, load_size * 8);

        if (bit_count == 0)
            return 0;

        // Read by loading a LoadInt, and then follow it up with a 1-byte read

        // of the tail if bit_offset pushed us over a byte boundary.

        const read_bytes = bytes[bit_offset / 8 ..];
        const val = @as(uN, @truncate(readIntLittle(LoadInt, read_bytes[0..load_size]) >> bit_shift));
        if (bit_shift > load_tail_bits) {
            const tail_bits = @as(Log2N, @intCast(bit_shift - load_tail_bits));
            const tail_byte = read_bytes[load_size];
            const tail_truncated = if (bit_count < 8) @as(uN, @truncate(tail_byte)) else @as(uN, tail_byte);
            return @as(T, @bitCast(val | (tail_truncated << (@as(Log2N, @truncate(bit_count)) -% tail_bits))));
        } else return @as(T, @bitCast(val));
    }

    fn readPackedIntBig(comptime T: type, bytes: []const u8, bit_offset: usize) T {
        const uN = std.meta.Int(.unsigned, @bitSizeOf(T));
        const Log2N = std.math.Log2Int(T);

        const bit_count = @as(usize, @bitSizeOf(T));
        const bit_shift = @as(u3, @intCast(bit_offset % 8));
        const byte_count = (@as(usize, bit_shift) + bit_count + 7) / 8;

        const load_size = (bit_count + 7) / 8;
        const load_tail_bits = @as(u3, @intCast((load_size * 8) - bit_count));
        const LoadInt = std.meta.Int(.unsigned, load_size * 8);

        if (bit_count == 0)
            return 0;

        // Read by loading a LoadInt, and then follow it up with a 1-byte read

        // of the tail if bit_offset pushed us over a byte boundary.

        const end = bytes.len - (bit_offset / 8);
        const read_bytes = bytes[(end - byte_count)..end];
        const val = @as(uN, @truncate(readIntBig(LoadInt, bytes[(end - load_size)..end][0..load_size]) >> bit_shift));
        if (bit_shift > load_tail_bits) {
            const tail_bits = @as(Log2N, @intCast(bit_shift - load_tail_bits));
            const tail_byte = if (bit_count < 8) @as(uN, @truncate(read_bytes[0])) else @as(uN, read_bytes[0]);
            return @as(T, @bitCast(val | (tail_byte << (@as(Log2N, @truncate(bit_count)) -% tail_bits))));
        } else return @as(T, @bitCast(val));
    }

    pub const readPackedIntNative = switch (native_endian) {
        .Little => readPackedIntLittle,
        .Big => readPackedIntBig,
    };

    pub const readPackedIntForeign = switch (native_endian) {
        .Little => readPackedIntBig,
        .Big => readPackedIntLittle,
    };

    /// Loads an integer from packed memory.
    /// Asserts that buffer contains at least bit_offset + @bitSizeOf(T) bits.
    ///
    /// Example:
    ///     const T = packed struct(u16){ a: u3, b: u7, c: u6 };
    ///     var st = T{ .a = 1, .b = 2, .c = 4 };
    ///     const b_field = readPackedInt(u7, std.mem.asBytes(&st), @bitOffsetOf(T, "b"), builtin.cpu.arch.endian());
    ///
    pub fn readPackedInt(comptime T: type, bytes: []const u8, bit_offset: usize, endian: Endian) T {
        switch (endian) {
            .Little => return readPackedIntLittle(T, bytes, bit_offset),
            .Big => return readPackedIntBig(T, bytes, bit_offset),
        }
    }

    /// Asserts that bytes.len >= @typeInfo(T).Int.bits / 8. Reads the integer starting from index 0
    /// and ignores extra bytes.
    /// The bit count of T must be evenly divisible by 8.
    pub fn readIntSlice(comptime T: type, bytes: []const u8, endian: Endian) T {
        const n = @divExact(@typeInfo(T).Int.bits, 8);
        assert(bytes.len >= n);
        return readInt(T, bytes[0..n], endian);
    }

    test "comptime read/write int" {
        comptime {
            var bytes: [2]u8 = undefined;
            writeIntLittle(u16, &bytes, 0x1234);
            const result = readIntBig(u16, &bytes);
            try testing.expect(result == 0x3412);
        }
        comptime {
            var bytes: [2]u8 = undefined;
            writeIntBig(u16, &bytes, 0x1234);
            const result = readIntLittle(u16, &bytes);
            try testing.expect(result == 0x3412);
        }
    }

    test "readIntBig and readIntLittle" {
        if (builtin.zig_backend == .stage2_c) return error.SkipZigTest;

        try testing.expect(readIntSliceBig(u0, &[_]u8{}) == 0x0);
        try testing.expect(readIntSliceLittle(u0, &[_]u8{}) == 0x0);

        try testing.expect(readIntSliceBig(u8, &[_]u8{0x32}) == 0x32);
        try testing.expect(readIntSliceLittle(u8, &[_]u8{0x12}) == 0x12);

        try testing.expect(readIntSliceBig(u16, &[_]u8{ 0x12, 0x34 }) == 0x1234);
        try testing.expect(readIntSliceLittle(u16, &[_]u8{ 0x12, 0x34 }) == 0x3412);

        try testing.expect(readIntSliceBig(u72, &[_]u8{ 0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0, 0x24 }) == 0x123456789abcdef024);
        try testing.expect(readIntSliceLittle(u72, &[_]u8{ 0xec, 0x10, 0x32, 0x54, 0x76, 0x98, 0xba, 0xdc, 0xfe }) == 0xfedcba9876543210ec);

        try testing.expect(readIntSliceBig(i8, &[_]u8{0xff}) == -1);
        try testing.expect(readIntSliceLittle(i8, &[_]u8{0xfe}) == -2);

        try testing.expect(readIntSliceBig(i16, &[_]u8{ 0xff, 0xfd }) == -3);
        try testing.expect(readIntSliceLittle(i16, &[_]u8{ 0xfc, 0xff }) == -4);
    }

    /// Writes an integer to memory, storing it in twos-complement.
    /// This function always succeeds, has defined behavior for all inputs, and
    /// accepts any integer bit width.
    /// This function stores in native endian, which means it is implemented as a simple
    /// memory store.
    pub fn writeIntNative(comptime T: type, buf: *[@as(u16, @intCast((@as(u17, @typeInfo(T).Int.bits) + 7) / 8))]u8, value: T) void {
        @as(*align(1) T, @ptrCast(buf)).* = value;
    }

    /// Writes an integer to memory, storing it in twos-complement.
    /// This function always succeeds, has defined behavior for all inputs, but
    /// the integer bit width must be divisible by 8.
    /// This function stores in foreign endian, which means it does a @byteSwap first.
    pub fn writeIntForeign(comptime T: type, buf: *[@divExact(@typeInfo(T).Int.bits, 8)]u8, value: T) void {
        writeIntNative(T, buf, @byteSwap(value));
    }

    pub const writeIntLittle = switch (native_endian) {
        .Little => writeIntNative,
        .Big => writeIntForeign,
    };

    pub const writeIntBig = switch (native_endian) {
        .Little => writeIntForeign,
        .Big => writeIntNative,
    };

    /// Writes an integer to memory, storing it in twos-complement.
    /// This function always succeeds, has defined behavior for all inputs, but
    /// the integer bit width must be divisible by 8.
    pub fn writeInt(comptime T: type, buffer: *[@divExact(@typeInfo(T).Int.bits, 8)]u8, value: T, endian: Endian) void {
        if (endian == native_endian) {
            return writeIntNative(T, buffer, value);
        } else {
            return writeIntForeign(T, buffer, value);
        }
    }

    fn writePackedIntLittle(comptime T: type, bytes: []u8, bit_offset: usize, value: T) void {
        const uN = std.meta.Int(.unsigned, @bitSizeOf(T));
        const Log2N = std.math.Log2Int(T);

        const bit_count = @as(usize, @bitSizeOf(T));
        const bit_shift = @as(u3, @intCast(bit_offset % 8));

        const store_size = (@bitSizeOf(T) + 7) / 8;
        const store_tail_bits = @as(u3, @intCast((store_size * 8) - bit_count));
        const StoreInt = std.meta.Int(.unsigned, store_size * 8);

        if (bit_count == 0)
            return;

        // Write by storing a StoreInt, and then follow it up with a 1-byte tail

        // if bit_offset pushed us over a byte boundary.

        const write_bytes = bytes[bit_offset / 8 ..];
        const head = write_bytes[0] & ((@as(u8, 1) << bit_shift) - 1);

        var write_value = (@as(StoreInt, @as(uN, @bitCast(value))) << bit_shift) | @as(StoreInt, @intCast(head));
        if (bit_shift > store_tail_bits) {
            const tail_len = @as(Log2N, @intCast(bit_shift - store_tail_bits));
            write_bytes[store_size] &= ~((@as(u8, 1) << @as(u3, @intCast(tail_len))) - 1);
            write_bytes[store_size] |= @as(u8, @intCast((@as(uN, @bitCast(value)) >> (@as(Log2N, @truncate(bit_count)) -% tail_len))));
        } else if (bit_shift < store_tail_bits) {
            const tail_len = store_tail_bits - bit_shift;
            const tail = write_bytes[store_size - 1] & (@as(u8, 0xfe) << (7 - tail_len));
            write_value |= @as(StoreInt, tail) << (8 * (store_size - 1));
        }

        writeIntLittle(StoreInt, write_bytes[0..store_size], write_value);
    }

    fn writePackedIntBig(comptime T: type, bytes: []u8, bit_offset: usize, value: T) void {
        const uN = std.meta.Int(.unsigned, @bitSizeOf(T));
        const Log2N = std.math.Log2Int(T);

        const bit_count = @as(usize, @bitSizeOf(T));
        const bit_shift = @as(u3, @intCast(bit_offset % 8));
        const byte_count = (bit_shift + bit_count + 7) / 8;

        const store_size = (@bitSizeOf(T) + 7) / 8;
        const store_tail_bits = @as(u3, @intCast((store_size * 8) - bit_count));
        const StoreInt = std.meta.Int(.unsigned, store_size * 8);

        if (bit_count == 0)
            return;

        // Write by storing a StoreInt, and then follow it up with a 1-byte tail

        // if bit_offset pushed us over a byte boundary.

        const end = bytes.len - (bit_offset / 8);
        const write_bytes = bytes[(end - byte_count)..end];
        const head = write_bytes[byte_count - 1] & ((@as(u8, 1) << bit_shift) - 1);

        var write_value = (@as(StoreInt, @as(uN, @bitCast(value))) << bit_shift) | @as(StoreInt, @intCast(head));
        if (bit_shift > store_tail_bits) {
            const tail_len = @as(Log2N, @intCast(bit_shift - store_tail_bits));
            write_bytes[0] &= ~((@as(u8, 1) << @as(u3, @intCast(tail_len))) - 1);
            write_bytes[0] |= @as(u8, @intCast((@as(uN, @bitCast(value)) >> (@as(Log2N, @truncate(bit_count)) -% tail_len))));
        } else if (bit_shift < store_tail_bits) {
            const tail_len = store_tail_bits - bit_shift;
            const tail = write_bytes[0] & (@as(u8, 0xfe) << (7 - tail_len));
            write_value |= @as(StoreInt, tail) << (8 * (store_size - 1));
        }

        writeIntBig(StoreInt, write_bytes[(byte_count - store_size)..][0..store_size], write_value);
    }

    pub const writePackedIntNative = switch (native_endian) {
        .Little => writePackedIntLittle,
        .Big => writePackedIntBig,
    };

    pub const writePackedIntForeign = switch (native_endian) {
        .Little => writePackedIntBig,
        .Big => writePackedIntLittle,
    };

    /// Stores an integer to packed memory.
    /// Asserts that buffer contains at least bit_offset + @bitSizeOf(T) bits.
    ///
    /// Example:
    ///     const T = packed struct(u16){ a: u3, b: u7, c: u6 };
    ///     var st = T{ .a = 1, .b = 2, .c = 4 };
    ///     // st.b = 0x7f;
    ///     writePackedInt(u7, std.mem.asBytes(&st), @bitOffsetOf(T, "b"), 0x7f, builtin.cpu.arch.endian());
    ///
    pub fn writePackedInt(comptime T: type, bytes: []u8, bit_offset: usize, value: T, endian: Endian) void {
        switch (endian) {
            .Little => writePackedIntLittle(T, bytes, bit_offset, value),
            .Big => writePackedIntBig(T, bytes, bit_offset, value),
        }
    }

    /// Writes a twos-complement little-endian integer to memory.
    /// Asserts that buf.len >= @typeInfo(T).Int.bits / 8.
    /// The bit count of T must be divisible by 8.
    /// Any extra bytes in buffer after writing the integer are set to zero. To
    /// avoid the branch to check for extra buffer bytes, use writeIntLittle
    /// instead.
    pub fn writeIntSliceLittle(comptime T: type, buffer: []u8, value: T) void {
        assert(buffer.len >= @divExact(@typeInfo(T).Int.bits, 8));

        if (@typeInfo(T).Int.bits == 0) {
            return @memset(buffer, 0);
        } else if (@typeInfo(T).Int.bits == 8) {
            @memset(buffer, 0);
            buffer[0] = @as(u8, @bitCast(value));
            return;
        }
        // TODO I want to call writeIntLittle here but comptime eval facilities aren't good enough

        const uint = std.meta.Int(.unsigned, @typeInfo(T).Int.bits);
        var bits = @as(uint, @bitCast(value));
        for (buffer) |*b| {
            b.* = @as(u8, @truncate(bits));
            bits >>= 8;
        }
    }

    /// Writes a twos-complement big-endian integer to memory.
    /// Asserts that buffer.len >= @typeInfo(T).Int.bits / 8.
    /// The bit count of T must be divisible by 8.
    /// Any extra bytes in buffer before writing the integer are set to zero. To
    /// avoid the branch to check for extra buffer bytes, use writeIntBig instead.
    pub fn writeIntSliceBig(comptime T: type, buffer: []u8, value: T) void {
        assert(buffer.len >= @divExact(@typeInfo(T).Int.bits, 8));

        if (@typeInfo(T).Int.bits == 0) {
            return @memset(buffer, 0);
        } else if (@typeInfo(T).Int.bits == 8) {
            @memset(buffer, 0);
            buffer[buffer.len - 1] = @as(u8, @bitCast(value));
            return;
        }

        // TODO I want to call writeIntBig here but comptime eval facilities aren't good enough

        const uint = std.meta.Int(.unsigned, @typeInfo(T).Int.bits);
        var bits = @as(uint, @bitCast(value));
        var index: usize = buffer.len;
        while (index != 0) {
            index -= 1;
            buffer[index] = @as(u8, @truncate(bits));
            bits >>= 8;
        }
    }

    pub const writeIntSliceNative = switch (native_endian) {
        .Little => writeIntSliceLittle,
        .Big => writeIntSliceBig,
    };

    pub const writeIntSliceForeign = switch (native_endian) {
        .Little => writeIntSliceBig,
        .Big => writeIntSliceLittle,
    };

    /// Writes a twos-complement integer to memory, with the specified endianness.
    /// Asserts that buf.len >= @typeInfo(T).Int.bits / 8.
    /// The bit count of T must be evenly divisible by 8.
    /// Any extra bytes in buffer not part of the integer are set to zero, with
    /// respect to endianness. To avoid the branch to check for extra buffer bytes,
    /// use writeInt instead.
    pub fn writeIntSlice(comptime T: type, buffer: []u8, value: T, endian: Endian) void {
        comptime assert(@typeInfo(T).Int.bits % 8 == 0);
        return switch (endian) {
            .Little => writeIntSliceLittle(T, buffer, value),
            .Big => writeIntSliceBig(T, buffer, value),
        };
    }

    /// Stores an integer to packed memory with provided bit_count, bit_offset, and signedness.
    /// If negative, the written value is sign-extended.
    ///
    /// Example:
    ///     const T = packed struct(u16){ a: u3, b: u7, c: u6 };
    ///     var st = T{ .a = 1, .b = 2, .c = 4 };
    ///     // st.b = 0x7f;
    ///     var value: u64 = 0x7f;
    ///     writeVarPackedInt(std.mem.asBytes(&st), @bitOffsetOf(T, "b"), 7, value, builtin.cpu.arch.endian());
    ///
    pub fn writeVarPackedInt(bytes: []u8, bit_offset: usize, bit_count: usize, value: anytype, endian: std.builtin.Endian) void {
        const T = @TypeOf(value);
        const uN = std.meta.Int(.unsigned, @bitSizeOf(T));

        const bit_shift = @as(u3, @intCast(bit_offset % 8));
        const write_size = (bit_count + bit_shift + 7) / 8;
        const lowest_byte = switch (endian) {
            .Big => bytes.len - (bit_offset / 8) - write_size,
            .Little => bit_offset / 8,
        };
        const write_bytes = bytes[lowest_byte..][0..write_size];

        if (write_size == 1) {
            // Single byte writes are handled specially, since we need to mask bits

            // on both ends of the byte.

            const mask = (@as(u8, 0xff) >> @as(u3, @intCast(8 - bit_count)));
            const new_bits = @as(u8, @intCast(@as(uN, @bitCast(value)) & mask)) << bit_shift;
            write_bytes[0] = (write_bytes[0] & ~(mask << bit_shift)) | new_bits;
            return;
        }

        var remaining: T = value;

        // Iterate bytes forward for Little-endian, backward for Big-endian

        const delta: i2 = if (endian == .Big) -1 else 1;
        const start = if (endian == .Big) @as(isize, @intCast(write_bytes.len - 1)) else 0;

        var i: isize = start; // isize for signed index arithmetic

        // Write first byte, using a mask to protects bits preceding bit_offset

        const head_mask = @as(u8, 0xff) >> bit_shift;
        write_bytes[@intCast(i)] &= ~(head_mask << bit_shift);
        write_bytes[@intCast(i)] |= @as(u8, @intCast(@as(uN, @bitCast(remaining)) & head_mask)) << bit_shift;
        remaining = math.shr(T, remaining, @as(u4, 8) - bit_shift);
        i += delta;

        // Write bytes[1..bytes.len - 1]

        if (@bitSizeOf(T) > 8) {
            const loop_end = start + delta * (@as(isize, @intCast(write_size)) - 1);
            while (i != loop_end) : (i += delta) {
                write_bytes[@as(usize, @intCast(i))] = @as(u8, @truncate(@as(uN, @bitCast(remaining))));
                remaining >>= 8;
            }
        }

        // Write last byte, using a mask to protect bits following bit_offset + bit_count

        const following_bits = -%@as(u3, @truncate(bit_shift + bit_count));
        const tail_mask = (@as(u8, 0xff) << following_bits) >> following_bits;
        write_bytes[@as(usize, @intCast(i))] &= ~tail_mask;
        write_bytes[@as(usize, @intCast(i))] |= @as(u8, @intCast(@as(uN, @bitCast(remaining)) & tail_mask));
    }

    test "writeIntBig and writeIntLittle" {
        if (builtin.zig_backend == .stage2_c) return error.SkipZigTest;

        var buf0: [0]u8 = undefined;
        var buf1: [1]u8 = undefined;
        var buf2: [2]u8 = undefined;
        var buf9: [9]u8 = undefined;

        writeIntBig(u0, &buf0, 0x0);
        try testing.expect(eql(u8, buf0[0..], &[_]u8{}));
        writeIntLittle(u0, &buf0, 0x0);
        try testing.expect(eql(u8, buf0[0..], &[_]u8{}));

        writeIntBig(u8, &buf1, 0x12);
        try testing.expect(eql(u8, buf1[0..], &[_]u8{0x12}));
        writeIntLittle(u8, &buf1, 0x34);
        try testing.expect(eql(u8, buf1[0..], &[_]u8{0x34}));

        writeIntBig(u16, &buf2, 0x1234);
        try testing.expect(eql(u8, buf2[0..], &[_]u8{ 0x12, 0x34 }));
        writeIntLittle(u16, &buf2, 0x5678);
        try testing.expect(eql(u8, buf2[0..], &[_]u8{ 0x78, 0x56 }));

        writeIntBig(u72, &buf9, 0x123456789abcdef024);
        try testing.expect(eql(u8, buf9[0..], &[_]u8{ 0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0, 0x24 }));
        writeIntLittle(u72, &buf9, 0xfedcba9876543210ec);
        try testing.expect(eql(u8, buf9[0..], &[_]u8{ 0xec, 0x10, 0x32, 0x54, 0x76, 0x98, 0xba, 0xdc, 0xfe }));

        writeIntBig(i8, &buf1, -1);
        try testing.expect(eql(u8, buf1[0..], &[_]u8{0xff}));
        writeIntLittle(i8, &buf1, -2);
        try testing.expect(eql(u8, buf1[0..], &[_]u8{0xfe}));

        writeIntBig(i16, &buf2, -3);
        try testing.expect(eql(u8, buf2[0..], &[_]u8{ 0xff, 0xfd }));
        writeIntLittle(i16, &buf2, -4);
        try testing.expect(eql(u8, buf2[0..], &[_]u8{ 0xfc, 0xff }));
    }

    /// Swap the byte order of all the members of the fields of a struct
    /// (Changing their endianness)
    pub fn byteSwapAllFields(comptime S: type, ptr: *S) void {
        if (@typeInfo(S) != .Struct) @compileError("byteSwapAllFields expects a struct as the first argument");
        inline for (std.meta.fields(S)) |f| {
            if (@typeInfo(f.type) == .Struct) {
                byteSwapAllFields(f.type, &@field(ptr, f.name));
            } else {
                @field(ptr, f.name) = @byteSwap(@field(ptr, f.name));
            }
        }
    }

    test "byteSwapAllFields" {
        const T = extern struct {
            f0: u8,
            f1: u16,
            f2: u32,
        };
        const K = extern struct {
            f0: u8,
            f1: T,
            f2: u16,
        };
        var s = T{
            .f0 = 0x12,
            .f1 = 0x1234,
            .f2 = 0x12345678,
        };
        var k = K{
            .f0 = 0x12,
            .f1 = s,
            .f2 = 0x1234,
        };
        byteSwapAllFields(T, &s);
        byteSwapAllFields(K, &k);
        try std.testing.expectEqual(T{
            .f0 = 0x12,
            .f1 = 0x3412,
            .f2 = 0x78563412,
        }, s);
        try std.testing.expectEqual(K{
            .f0 = 0x12,
            .f1 = s,
            .f2 = 0x3412,
        }, k);
    }

    /// Deprecated: use `tokenizeAny`, `tokenizeSequence`, or `tokenizeScalar`
    pub const tokenize = tokenizeAny;

    /// Returns an iterator that iterates over the slices of `buffer` that are not
    /// any of the items in `delimiters`.
    ///
    /// `tokenizeAny(u8, "   abc|def ||  ghi  ", " |")` will return slices
    /// for "abc", "def", "ghi", null, in that order.
    ///
    /// If `buffer` is empty, the iterator will return null.
    /// If none of `delimiters` exist in buffer,
    /// the iterator will return `buffer`, null, in that order.
    ///
    /// See also: `tokenizeSequence`, `tokenizeScalar`,
    ///           `splitSequence`,`splitAny`, `splitScalar`,
    ///           `splitBackwardsSequence`, `splitBackwardsAny`, and `splitBackwardsScalar`
    pub fn tokenizeAny(comptime T: type, buffer: []const T, delimiters: []const T) TokenIterator(T, .any) {
        return .{
            .index = 0,
            .buffer = buffer,
            .delimiter = delimiters,
        };
    }

    /// Returns an iterator that iterates over the slices of `buffer` that are not
    /// the sequence in `delimiter`.
    ///
    /// `tokenizeSequence(u8, "<>abc><def<><>ghi", "<>")` will return slices
    /// for "abc><def", "ghi", null, in that order.
    ///
    /// If `buffer` is empty, the iterator will return null.
    /// If `delimiter` does not exist in buffer,
    /// the iterator will return `buffer`, null, in that order.
    /// The delimiter length must not be zero.
    ///
    /// See also: `tokenizeAny`, `tokenizeScalar`,
    ///           `splitSequence`,`splitAny`, and `splitScalar`
    ///           `splitBackwardsSequence`, `splitBackwardsAny`, and `splitBackwardsScalar`
    pub fn tokenizeSequence(comptime T: type, buffer: []const T, delimiter: []const T) TokenIterator(T, .sequence) {
        assert(delimiter.len != 0);
        return .{
            .index = 0,
            .buffer = buffer,
            .delimiter = delimiter,
        };
    }

    /// Returns an iterator that iterates over the slices of `buffer` that are not
    /// `delimiter`.
    ///
    /// `tokenizeScalar(u8, "   abc def     ghi  ", ' ')` will return slices
    /// for "abc", "def", "ghi", null, in that order.
    ///
    /// If `buffer` is empty, the iterator will return null.
    /// If `delimiter` does not exist in buffer,
    /// the iterator will return `buffer`, null, in that order.
    ///
    /// See also: `tokenizeAny`, `tokenizeSequence`,
    ///           `splitSequence`,`splitAny`, and `splitScalar`
    ///           `splitBackwardsSequence`, `splitBackwardsAny`, and `splitBackwardsScalar`
    pub fn tokenizeScalar(comptime T: type, buffer: []const T, delimiter: T) TokenIterator(T, .scalar) {
        return .{
            .index = 0,
            .buffer = buffer,
            .delimiter = delimiter,
        };
    }

    test "tokenizeScalar" {
        var it = tokenizeScalar(u8, "   abc def   ghi  ", ' ');
        try testing.expect(eql(u8, it.next().?, "abc"));
        try testing.expect(eql(u8, it.peek().?, "def"));
        try testing.expect(eql(u8, it.next().?, "def"));
        try testing.expect(eql(u8, it.next().?, "ghi"));
        try testing.expect(it.next() == null);

        it = tokenizeScalar(u8, "..\\bob", '\\');
        try testing.expect(eql(u8, it.next().?, ".."));
        try testing.expect(eql(u8, "..", "..\\bob"[0..it.index]));
        try testing.expect(eql(u8, it.next().?, "bob"));
        try testing.expect(it.next() == null);

        it = tokenizeScalar(u8, "//a/b", '/');
        try testing.expect(eql(u8, it.next().?, "a"));
        try testing.expect(eql(u8, it.next().?, "b"));
        try testing.expect(eql(u8, "//a/b", "//a/b"[0..it.index]));
        try testing.expect(it.next() == null);

        it = tokenizeScalar(u8, "|", '|');
        try testing.expect(it.next() == null);
        try testing.expect(it.peek() == null);

        it = tokenizeScalar(u8, "", '|');
        try testing.expect(it.next() == null);
        try testing.expect(it.peek() == null);

        it = tokenizeScalar(u8, "hello", ' ');
        try testing.expect(eql(u8, it.next().?, "hello"));
        try testing.expect(it.next() == null);

        var it16 = tokenizeScalar(
            u16,
            std.unicode.utf8ToUtf16LeStringLiteral("hello"),
            ' ',
        );
        try testing.expect(eql(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("hello")));
        try testing.expect(it16.next() == null);
    }

    test "tokenizeAny" {
        var it = tokenizeAny(u8, "a|b,c/d e", " /,|");
        try testing.expect(eql(u8, it.next().?, "a"));
        try testing.expect(eql(u8, it.peek().?, "b"));
        try testing.expect(eql(u8, it.next().?, "b"));
        try testing.expect(eql(u8, it.next().?, "c"));
        try testing.expect(eql(u8, it.next().?, "d"));
        try testing.expect(eql(u8, it.next().?, "e"));
        try testing.expect(it.next() == null);
        try testing.expect(it.peek() == null);

        it = tokenizeAny(u8, "hello", "");
        try testing.expect(eql(u8, it.next().?, "hello"));
        try testing.expect(it.next() == null);

        var it16 = tokenizeAny(
            u16,
            std.unicode.utf8ToUtf16LeStringLiteral("a|b,c/d e"),
            std.unicode.utf8ToUtf16LeStringLiteral(" /,|"),
        );
        try testing.expect(eql(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("a")));
        try testing.expect(eql(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("b")));
        try testing.expect(eql(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("c")));
        try testing.expect(eql(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("d")));
        try testing.expect(eql(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("e")));
        try testing.expect(it16.next() == null);
    }

    test "tokenizeSequence" {
        var it = tokenizeSequence(u8, "a<>b<><>c><>d><", "<>");
        try testing.expectEqualStrings("a", it.next().?);
        try testing.expectEqualStrings("b", it.peek().?);
        try testing.expectEqualStrings("b", it.next().?);
        try testing.expectEqualStrings("c>", it.next().?);
        try testing.expectEqualStrings("d><", it.next().?);
        try testing.expect(it.next() == null);
        try testing.expect(it.peek() == null);

        var it16 = tokenizeSequence(
            u16,
            std.unicode.utf8ToUtf16LeStringLiteral("a<>b<><>c><>d><"),
            std.unicode.utf8ToUtf16LeStringLiteral("<>"),
        );
        try testing.expect(eql(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("a")));
        try testing.expect(eql(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("b")));
        try testing.expect(eql(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("c>")));
        try testing.expect(eql(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("d><")));
        try testing.expect(it16.next() == null);
    }

    test "tokenize (reset)" {
        {
            var it = tokenizeAny(u8, "   abc def   ghi  ", " ");
            try testing.expect(eql(u8, it.next().?, "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));

            it.reset();

            try testing.expect(eql(u8, it.next().?, "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));
            try testing.expect(it.next() == null);
        }
        {
            var it = tokenizeSequence(u8, "<><>abc<>def<><>ghi<>", "<>");
            try testing.expect(eql(u8, it.next().?, "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));

            it.reset();

            try testing.expect(eql(u8, it.next().?, "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));
            try testing.expect(it.next() == null);
        }
        {
            var it = tokenizeScalar(u8, "   abc def   ghi  ", ' ');
            try testing.expect(eql(u8, it.next().?, "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));

            it.reset();

            try testing.expect(eql(u8, it.next().?, "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));
            try testing.expect(it.next() == null);
        }
    }

    /// Deprecated: use `splitSequence`, `splitAny`, or `splitScalar`
    pub const split = splitSequence;

    /// Returns an iterator that iterates over the slices of `buffer` that
    /// are separated by the byte sequence in `delimiter`.
    ///
    /// `splitSequence(u8, "abc||def||||ghi", "||")` will return slices
    /// for "abc", "def", "", "ghi", null, in that order.
    ///
    /// If `delimiter` does not exist in buffer,
    /// the iterator will return `buffer`, null, in that order.
    /// The delimiter length must not be zero.
    ///
    /// See also: `splitAny`, `splitScalar`, `splitBackwardsSequence`,
    ///           `splitBackwardsAny`,`splitBackwardsScalar`,
    ///           `tokenizeAny`, `tokenizeSequence`, and `tokenizeScalar`.
    pub fn splitSequence(comptime T: type, buffer: []const T, delimiter: []const T) SplitIterator(T, .sequence) {
        assert(delimiter.len != 0);
        return .{
            .index = 0,
            .buffer = buffer,
            .delimiter = delimiter,
        };
    }

    /// Returns an iterator that iterates over the slices of `buffer` that
    /// are separated by any item in `delimiters`.
    ///
    /// `splitAny(u8, "abc,def||ghi", "|,")` will return slices
    /// for "abc", "def", "", "ghi", null, in that order.
    ///
    /// If none of `delimiters` exist in buffer,
    /// the iterator will return `buffer`, null, in that order.
    ///
    /// See also: `splitSequence`, `splitScalar`, `splitBackwardsSequence`,
    ///           `splitBackwardsAny`,`splitBackwardsScalar`,
    ///           `tokenizeAny`, `tokenizeSequence`, and `tokenizeScalar`.
    pub fn splitAny(comptime T: type, buffer: []const T, delimiters: []const T) SplitIterator(T, .any) {
        return .{
            .index = 0,
            .buffer = buffer,
            .delimiter = delimiters,
        };
    }

    /// Returns an iterator that iterates over the slices of `buffer` that
    /// are separated by `delimiter`.
    ///
    /// `splitScalar(u8, "abc|def||ghi", '|')` will return slices
    /// for "abc", "def", "", "ghi", null, in that order.
    ///
    /// If `delimiter` does not exist in buffer,
    /// the iterator will return `buffer`, null, in that order.
    ///
    /// See also: `splitSequence`, `splitAny`, `splitBackwardsSequence`,
    ///           `splitBackwardsAny`,`splitBackwardsScalar`,
    ///           `tokenizeAny`, `tokenizeSequence`, and `tokenizeScalar`.
    pub fn splitScalar(comptime T: type, buffer: []const T, delimiter: T) SplitIterator(T, .scalar) {
        return .{
            .index = 0,
            .buffer = buffer,
            .delimiter = delimiter,
        };
    }

    test "splitScalar" {
        var it = splitScalar(u8, "abc|def||ghi", '|');
        try testing.expectEqualSlices(u8, it.rest(), "abc|def||ghi");
        try testing.expectEqualSlices(u8, it.first(), "abc");

        try testing.expectEqualSlices(u8, it.rest(), "def||ghi");
        try testing.expectEqualSlices(u8, it.peek().?, "def");
        try testing.expectEqualSlices(u8, it.next().?, "def");

        try testing.expectEqualSlices(u8, it.rest(), "|ghi");
        try testing.expectEqualSlices(u8, it.next().?, "");

        try testing.expectEqualSlices(u8, it.rest(), "ghi");
        try testing.expectEqualSlices(u8, it.peek().?, "ghi");
        try testing.expectEqualSlices(u8, it.next().?, "ghi");

        try testing.expectEqualSlices(u8, it.rest(), "");
        try testing.expect(it.peek() == null);
        try testing.expect(it.next() == null);

        it = splitScalar(u8, "", '|');
        try testing.expectEqualSlices(u8, it.first(), "");
        try testing.expect(it.next() == null);

        it = splitScalar(u8, "|", '|');
        try testing.expectEqualSlices(u8, it.first(), "");
        try testing.expectEqualSlices(u8, it.next().?, "");
        try testing.expect(it.peek() == null);
        try testing.expect(it.next() == null);

        it = splitScalar(u8, "hello", ' ');
        try testing.expectEqualSlices(u8, it.first(), "hello");
        try testing.expect(it.next() == null);

        var it16 = splitScalar(
            u16,
            std.unicode.utf8ToUtf16LeStringLiteral("hello"),
            ' ',
        );
        try testing.expectEqualSlices(u16, it16.first(), std.unicode.utf8ToUtf16LeStringLiteral("hello"));
        try testing.expect(it16.next() == null);
    }

    test "splitSequence" {
        var it = splitSequence(u8, "a, b ,, c, d, e", ", ");
        try testing.expectEqualSlices(u8, it.first(), "a");
        try testing.expectEqualSlices(u8, it.rest(), "b ,, c, d, e");
        try testing.expectEqualSlices(u8, it.next().?, "b ,");
        try testing.expectEqualSlices(u8, it.next().?, "c");
        try testing.expectEqualSlices(u8, it.next().?, "d");
        try testing.expectEqualSlices(u8, it.next().?, "e");
        try testing.expect(it.next() == null);

        var it16 = splitSequence(
            u16,
            std.unicode.utf8ToUtf16LeStringLiteral("a, b ,, c, d, e"),
            std.unicode.utf8ToUtf16LeStringLiteral(", "),
        );
        try testing.expectEqualSlices(u16, it16.first(), std.unicode.utf8ToUtf16LeStringLiteral("a"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("b ,"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("c"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("d"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("e"));
        try testing.expect(it16.next() == null);
    }

    test "splitAny" {
        var it = splitAny(u8, "a,b, c d e", ", ");
        try testing.expectEqualSlices(u8, it.first(), "a");
        try testing.expectEqualSlices(u8, it.rest(), "b, c d e");
        try testing.expectEqualSlices(u8, it.next().?, "b");
        try testing.expectEqualSlices(u8, it.next().?, "");
        try testing.expectEqualSlices(u8, it.next().?, "c");
        try testing.expectEqualSlices(u8, it.next().?, "d");
        try testing.expectEqualSlices(u8, it.next().?, "e");
        try testing.expect(it.next() == null);

        it = splitAny(u8, "hello", "");
        try testing.expect(eql(u8, it.next().?, "hello"));
        try testing.expect(it.next() == null);

        var it16 = splitAny(
            u16,
            std.unicode.utf8ToUtf16LeStringLiteral("a,b, c d e"),
            std.unicode.utf8ToUtf16LeStringLiteral(", "),
        );
        try testing.expectEqualSlices(u16, it16.first(), std.unicode.utf8ToUtf16LeStringLiteral("a"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("b"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral(""));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("c"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("d"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("e"));
        try testing.expect(it16.next() == null);
    }

    test "split (reset)" {
        {
            var it = splitSequence(u8, "abc def ghi", " ");
            try testing.expect(eql(u8, it.first(), "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));

            it.reset();

            try testing.expect(eql(u8, it.first(), "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));
            try testing.expect(it.next() == null);
        }
        {
            var it = splitAny(u8, "abc def,ghi", " ,");
            try testing.expect(eql(u8, it.first(), "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));

            it.reset();

            try testing.expect(eql(u8, it.first(), "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));
            try testing.expect(it.next() == null);
        }
        {
            var it = splitScalar(u8, "abc def ghi", ' ');
            try testing.expect(eql(u8, it.first(), "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));

            it.reset();

            try testing.expect(eql(u8, it.first(), "abc"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "ghi"));
            try testing.expect(it.next() == null);
        }
    }

    /// Deprecated: use `splitBackwardsSequence`, `splitBackwardsAny`, or `splitBackwardsScalar`
    pub const splitBackwards = splitBackwardsSequence;

    /// Returns an iterator that iterates backwards over the slices of `buffer` that
    /// are separated by the sequence in `delimiter`.
    ///
    /// `splitBackwardsSequence(u8, "abc||def||||ghi", "||")` will return slices
    /// for "ghi", "", "def", "abc", null, in that order.
    ///
    /// If `delimiter` does not exist in buffer,
    /// the iterator will return `buffer`, null, in that order.
    /// The delimiter length must not be zero.
    ///
    /// See also: `splitBackwardsAny`, `splitBackwardsScalar`,
    ///           `splitSequence`, `splitAny`,`splitScalar`,
    ///           `tokenizeAny`, `tokenizeSequence`, and `tokenizeScalar`.
    pub fn splitBackwardsSequence(comptime T: type, buffer: []const T, delimiter: []const T) SplitBackwardsIterator(T, .sequence) {
        assert(delimiter.len != 0);
        return .{
            .index = buffer.len,
            .buffer = buffer,
            .delimiter = delimiter,
        };
    }

    /// Returns an iterator that iterates backwards over the slices of `buffer` that
    /// are separated by any item in `delimiters`.
    ///
    /// `splitBackwardsAny(u8, "abc,def||ghi", "|,")` will return slices
    /// for "ghi", "", "def", "abc", null, in that order.
    ///
    /// If none of `delimiters` exist in buffer,
    /// the iterator will return `buffer`, null, in that order.
    ///
    /// See also: `splitBackwardsSequence`, `splitBackwardsScalar`,
    ///           `splitSequence`, `splitAny`,`splitScalar`,
    ///           `tokenizeAny`, `tokenizeSequence`, and `tokenizeScalar`.
    pub fn splitBackwardsAny(comptime T: type, buffer: []const T, delimiters: []const T) SplitBackwardsIterator(T, .any) {
        return .{
            .index = buffer.len,
            .buffer = buffer,
            .delimiter = delimiters,
        };
    }

    /// Returns an iterator that iterates backwards over the slices of `buffer` that
    /// are separated by `delimiter`.
    ///
    /// `splitBackwardsScalar(u8, "abc|def||ghi", '|')` will return slices
    /// for "ghi", "", "def", "abc", null, in that order.
    ///
    /// If `delimiter` does not exist in buffer,
    /// the iterator will return `buffer`, null, in that order.
    ///
    /// See also: `splitBackwardsSequence`, `splitBackwardsAny`,
    ///           `splitSequence`, `splitAny`,`splitScalar`,
    ///           `tokenizeAny`, `tokenizeSequence`, and `tokenizeScalar`.
    pub fn splitBackwardsScalar(comptime T: type, buffer: []const T, delimiter: T) SplitBackwardsIterator(T, .scalar) {
        return .{
            .index = buffer.len,
            .buffer = buffer,
            .delimiter = delimiter,
        };
    }

    test "splitBackwardsScalar" {
        var it = splitBackwardsScalar(u8, "abc|def||ghi", '|');
        try testing.expectEqualSlices(u8, it.rest(), "abc|def||ghi");
        try testing.expectEqualSlices(u8, it.first(), "ghi");

        try testing.expectEqualSlices(u8, it.rest(), "abc|def|");
        try testing.expectEqualSlices(u8, it.next().?, "");

        try testing.expectEqualSlices(u8, it.rest(), "abc|def");
        try testing.expectEqualSlices(u8, it.next().?, "def");

        try testing.expectEqualSlices(u8, it.rest(), "abc");
        try testing.expectEqualSlices(u8, it.next().?, "abc");

        try testing.expectEqualSlices(u8, it.rest(), "");
        try testing.expect(it.next() == null);

        it = splitBackwardsScalar(u8, "", '|');
        try testing.expectEqualSlices(u8, it.first(), "");
        try testing.expect(it.next() == null);

        it = splitBackwardsScalar(u8, "|", '|');
        try testing.expectEqualSlices(u8, it.first(), "");
        try testing.expectEqualSlices(u8, it.next().?, "");
        try testing.expect(it.next() == null);

        it = splitBackwardsScalar(u8, "hello", ' ');
        try testing.expectEqualSlices(u8, it.first(), "hello");
        try testing.expect(it.next() == null);

        var it16 = splitBackwardsScalar(
            u16,
            std.unicode.utf8ToUtf16LeStringLiteral("hello"),
            ' ',
        );
        try testing.expectEqualSlices(u16, it16.first(), std.unicode.utf8ToUtf16LeStringLiteral("hello"));
        try testing.expect(it16.next() == null);
    }

    test "splitBackwardsSequence" {
        var it = splitBackwardsSequence(u8, "a, b ,, c, d, e", ", ");
        try testing.expectEqualSlices(u8, it.rest(), "a, b ,, c, d, e");
        try testing.expectEqualSlices(u8, it.first(), "e");

        try testing.expectEqualSlices(u8, it.rest(), "a, b ,, c, d");
        try testing.expectEqualSlices(u8, it.next().?, "d");

        try testing.expectEqualSlices(u8, it.rest(), "a, b ,, c");
        try testing.expectEqualSlices(u8, it.next().?, "c");

        try testing.expectEqualSlices(u8, it.rest(), "a, b ,");
        try testing.expectEqualSlices(u8, it.next().?, "b ,");

        try testing.expectEqualSlices(u8, it.rest(), "a");
        try testing.expectEqualSlices(u8, it.next().?, "a");

        try testing.expectEqualSlices(u8, it.rest(), "");
        try testing.expect(it.next() == null);

        var it16 = splitBackwardsSequence(
            u16,
            std.unicode.utf8ToUtf16LeStringLiteral("a, b ,, c, d, e"),
            std.unicode.utf8ToUtf16LeStringLiteral(", "),
        );
        try testing.expectEqualSlices(u16, it16.first(), std.unicode.utf8ToUtf16LeStringLiteral("e"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("d"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("c"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("b ,"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("a"));
        try testing.expect(it16.next() == null);
    }

    test "splitBackwardsAny" {
        var it = splitBackwardsAny(u8, "a,b, c d e", ", ");
        try testing.expectEqualSlices(u8, it.rest(), "a,b, c d e");
        try testing.expectEqualSlices(u8, it.first(), "e");

        try testing.expectEqualSlices(u8, it.rest(), "a,b, c d");
        try testing.expectEqualSlices(u8, it.next().?, "d");

        try testing.expectEqualSlices(u8, it.rest(), "a,b, c");
        try testing.expectEqualSlices(u8, it.next().?, "c");

        try testing.expectEqualSlices(u8, it.rest(), "a,b,");
        try testing.expectEqualSlices(u8, it.next().?, "");

        try testing.expectEqualSlices(u8, it.rest(), "a,b");
        try testing.expectEqualSlices(u8, it.next().?, "b");

        try testing.expectEqualSlices(u8, it.rest(), "a");
        try testing.expectEqualSlices(u8, it.next().?, "a");

        try testing.expectEqualSlices(u8, it.rest(), "");
        try testing.expect(it.next() == null);

        var it16 = splitBackwardsAny(
            u16,
            std.unicode.utf8ToUtf16LeStringLiteral("a,b, c d e"),
            std.unicode.utf8ToUtf16LeStringLiteral(", "),
        );
        try testing.expectEqualSlices(u16, it16.first(), std.unicode.utf8ToUtf16LeStringLiteral("e"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("d"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("c"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral(""));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("b"));
        try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("a"));
        try testing.expect(it16.next() == null);
    }

    test "splitBackwards (reset)" {
        {
            var it = splitBackwardsSequence(u8, "abc def ghi", " ");
            try testing.expect(eql(u8, it.first(), "ghi"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "abc"));

            it.reset();

            try testing.expect(eql(u8, it.first(), "ghi"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "abc"));
            try testing.expect(it.next() == null);
        }
        {
            var it = splitBackwardsAny(u8, "abc def,ghi", " ,");
            try testing.expect(eql(u8, it.first(), "ghi"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "abc"));

            it.reset();

            try testing.expect(eql(u8, it.first(), "ghi"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "abc"));
            try testing.expect(it.next() == null);
        }
        {
            var it = splitBackwardsScalar(u8, "abc def ghi", ' ');
            try testing.expect(eql(u8, it.first(), "ghi"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "abc"));

            it.reset();

            try testing.expect(eql(u8, it.first(), "ghi"));
            try testing.expect(eql(u8, it.next().?, "def"));
            try testing.expect(eql(u8, it.next().?, "abc"));
            try testing.expect(it.next() == null);
        }
    }

    /// Returns an iterator with a sliding window of slices for `buffer`.
    /// The sliding window has length `size` and on every iteration moves
    /// forward by `advance`.
    ///
    /// Extract data for moving average with:
    /// `window(u8, "abcdefg", 3, 1)` will return slices
    /// "abc", "bcd", "cde", "def", "efg", null, in that order.
    ///
    /// Chunk or split every N items with:
    /// `window(u8, "abcdefg", 3, 3)` will return slices
    /// "abc", "def", "g", null, in that order.
    ///
    /// Pick every even index with:
    /// `window(u8, "abcdefg", 1, 2)` will return slices
    /// "a", "c", "e", "g" null, in that order.
    ///
    /// The `size` and `advance` must be not be zero.
    pub fn window(comptime T: type, buffer: []const T, size: usize, advance: usize) WindowIterator(T) {
        assert(size != 0);
        assert(advance != 0);
        return .{
            .index = 0,
            .buffer = buffer,
            .size = size,
            .advance = advance,
        };
    }

    test "window" {
        {
            // moving average size 3

            var it = window(u8, "abcdefg", 3, 1);
            try testing.expectEqualSlices(u8, it.next().?, "abc");
            try testing.expectEqualSlices(u8, it.next().?, "bcd");
            try testing.expectEqualSlices(u8, it.next().?, "cde");
            try testing.expectEqualSlices(u8, it.next().?, "def");
            try testing.expectEqualSlices(u8, it.next().?, "efg");
            try testing.expectEqual(it.next(), null);

            // multibyte

            var it16 = window(u16, std.unicode.utf8ToUtf16LeStringLiteral("abcdefg"), 3, 1);
            try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("abc"));
            try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("bcd"));
            try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("cde"));
            try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("def"));
            try testing.expectEqualSlices(u16, it16.next().?, std.unicode.utf8ToUtf16LeStringLiteral("efg"));
            try testing.expectEqual(it16.next(), null);
        }

        {
            // chunk/split every 3

            var it = window(u8, "abcdefg", 3, 3);
            try testing.expectEqualSlices(u8, it.next().?, "abc");
            try testing.expectEqualSlices(u8, it.next().?, "def");
            try testing.expectEqualSlices(u8, it.next().?, "g");
            try testing.expectEqual(it.next(), null);
        }

        {
            // pick even

            var it = window(u8, "abcdefg", 1, 2);
            try testing.expectEqualSlices(u8, it.next().?, "a");
            try testing.expectEqualSlices(u8, it.next().?, "c");
            try testing.expectEqualSlices(u8, it.next().?, "e");
            try testing.expectEqualSlices(u8, it.next().?, "g");
            try testing.expectEqual(it.next(), null);
        }

        {
            // empty

            var it = window(u8, "", 1, 1);
            try testing.expectEqualSlices(u8, it.next().?, "");
            try testing.expectEqual(it.next(), null);

            it = window(u8, "", 10, 1);
            try testing.expectEqualSlices(u8, it.next().?, "");
            try testing.expectEqual(it.next(), null);

            it = window(u8, "", 1, 10);
            try testing.expectEqualSlices(u8, it.next().?, "");
            try testing.expectEqual(it.next(), null);

            it = window(u8, "", 10, 10);
            try testing.expectEqualSlices(u8, it.next().?, "");
            try testing.expectEqual(it.next(), null);
        }

        {
            // first

            var it = window(u8, "abcdefg", 3, 3);
            try testing.expectEqualSlices(u8, it.first(), "abc");
            it.reset();
            try testing.expectEqualSlices(u8, it.next().?, "abc");
        }

        {
            // reset

            var it = window(u8, "abcdefg", 3, 3);
            try testing.expectEqualSlices(u8, it.next().?, "abc");
            try testing.expectEqualSlices(u8, it.next().?, "def");
            try testing.expectEqualSlices(u8, it.next().?, "g");
            try testing.expectEqual(it.next(), null);

            it.reset();
            try testing.expectEqualSlices(u8, it.next().?, "abc");
            try testing.expectEqualSlices(u8, it.next().?, "def");
            try testing.expectEqualSlices(u8, it.next().?, "g");
            try testing.expectEqual(it.next(), null);
        }
    }

    pub fn WindowIterator(comptime T: type) type {
        return struct {
            buffer: []const T,
            index: ?usize,
            size: usize,
            advance: usize,

            const Self = @This();

            /// Returns a slice of the first window. This never fails.
            /// Call this only to get the first window and then use `next` to get
            /// all subsequent windows.
            pub fn first(self: *Self) []const T {
                assert(self.index.? == 0);
                return self.next().?;
            }

            /// Returns a slice of the next window, or null if window is at end.
            pub fn next(self: *Self) ?[]const T {
                const start = self.index orelse return null;
                const next_index = start + self.advance;
                const end = if (start + self.size < self.buffer.len and next_index < self.buffer.len) blk: {
                    self.index = next_index;
                    break :blk start + self.size;
                } else blk: {
                    self.index = null;
                    break :blk self.buffer.len;
                };

                return self.buffer[start..end];
            }

            /// Resets the iterator to the initial window.
            pub fn reset(self: *Self) void {
                self.index = 0;
            }
        };
    }

    pub fn startsWith(comptime T: type, haystack: []const T, needle: []const T) bool {
        return if (needle.len > haystack.len) false else eql(T, haystack[0..needle.len], needle);
    }

    test "startsWith" {
        try testing.expect(startsWith(u8, "Bob", "Bo"));
        try testing.expect(!startsWith(u8, "Needle in haystack", "haystack"));
    }

    pub fn endsWith(comptime T: type, haystack: []const T, needle: []const T) bool {
        return if (needle.len > haystack.len) false else eql(T, haystack[haystack.len - needle.len ..], needle);
    }

    test "endsWith" {
        try testing.expect(endsWith(u8, "Needle in haystack", "haystack"));
        try testing.expect(!endsWith(u8, "Bob", "Bo"));
    }

    pub const DelimiterType = enum { sequence, any, scalar };

    pub fn TokenIterator(comptime T: type, comptime delimiter_type: DelimiterType) type {
        return struct {
            buffer: []const T,
            delimiter: switch (delimiter_type) {
                .sequence, .any => []const T,
                .scalar => T,
            },
            index: usize,

            const Self = @This();

            /// Returns a slice of the current token, or null if tokenization is
            /// complete, and advances to the next token.
            pub fn next(self: *Self) ?[]const T {
                const result = self.peek() orelse return null;
                self.index += result.len;
                return result;
            }

            /// Returns a slice of the current token, or null if tokenization is
            /// complete. Does not advance to the next token.
            pub fn peek(self: *Self) ?[]const T {
                // move to beginning of token

                while (self.index < self.buffer.len and self.isDelimiter(self.index)) : (self.index += switch (delimiter_type) {
                    .sequence => self.delimiter.len,
                    .any, .scalar => 1,
                }) {}
                const start = self.index;
                if (start == self.buffer.len) {
                    return null;
                }

                // move to end of token

                var end = start;
                while (end < self.buffer.len and !self.isDelimiter(end)) : (end += 1) {}

                return self.buffer[start..end];
            }

            /// Returns a slice of the remaining bytes. Does not affect iterator state.
            pub fn rest(self: Self) []const T {
                // move to beginning of token

                var index: usize = self.index;
                while (index < self.buffer.len and self.isDelimiter(index)) : (index += switch (delimiter_type) {
                    .sequence => self.delimiter.len,
                    .any, .scalar => 1,
                }) {}
                return self.buffer[index..];
            }

            /// Resets the iterator to the initial token.
            pub fn reset(self: *Self) void {
                self.index = 0;
            }

            fn isDelimiter(self: Self, index: usize) bool {
                switch (delimiter_type) {
                    .sequence => return startsWith(T, self.buffer[index..], self.delimiter),
                    .any => {
                        const item = self.buffer[index];
                        for (self.delimiter) |delimiter_item| {
                            if (item == delimiter_item) {
                                return true;
                            }
                        }
                        return false;
                    },
                    .scalar => return self.buffer[index] == self.delimiter,
                }
            }
        };
    }

    pub fn SplitIterator(comptime T: type, comptime delimiter_type: DelimiterType) type {
        return struct {
            buffer: []const T,
            index: ?usize,
            delimiter: switch (delimiter_type) {
                .sequence, .any => []const T,
                .scalar => T,
            },

            const Self = @This();

            /// Returns a slice of the first field. This never fails.
            /// Call this only to get the first field and then use `next` to get all subsequent fields.
            pub fn first(self: *Self) []const T {
                assert(self.index.? == 0);
                return self.next().?;
            }

            /// Returns a slice of the next field, or null if splitting is complete.
            pub fn next(self: *Self) ?[]const T {
                const start = self.index orelse return null;
                const end = if (switch (delimiter_type) {
                    .sequence => indexOfPos(T, self.buffer, start, self.delimiter),
                    .any => indexOfAnyPos(T, self.buffer, start, self.delimiter),
                    .scalar => indexOfScalarPos(T, self.buffer, start, self.delimiter),
                }) |delim_start| blk: {
                    self.index = delim_start + switch (delimiter_type) {
                        .sequence => self.delimiter.len,
                        .any, .scalar => 1,
                    };
                    break :blk delim_start;
                } else blk: {
                    self.index = null;
                    break :blk self.buffer.len;
                };
                return self.buffer[start..end];
            }

            /// Returns a slice of the next field, or null if splitting is complete.
            /// This method does not alter self.index.
            pub fn peek(self: *Self) ?[]const T {
                const start = self.index orelse return null;
                const end = if (switch (delimiter_type) {
                    .sequence => indexOfPos(T, self.buffer, start, self.delimiter),
                    .any => indexOfAnyPos(T, self.buffer, start, self.delimiter),
                    .scalar => indexOfScalarPos(T, self.buffer, start, self.delimiter),
                }) |delim_start| delim_start else self.buffer.len;
                return self.buffer[start..end];
            }

            /// Returns a slice of the remaining bytes. Does not affect iterator state.
            pub fn rest(self: Self) []const T {
                const end = self.buffer.len;
                const start = self.index orelse end;
                return self.buffer[start..end];
            }

            /// Resets the iterator to the initial slice.
            pub fn reset(self: *Self) void {
                self.index = 0;
            }
        };
    }

    pub fn SplitBackwardsIterator(comptime T: type, comptime delimiter_type: DelimiterType) type {
        return struct {
            buffer: []const T,
            index: ?usize,
            delimiter: switch (delimiter_type) {
                .sequence, .any => []const T,
                .scalar => T,
            },

            const Self = @This();

            /// Returns a slice of the first field. This never fails.
            /// Call this only to get the first field and then use `next` to get all subsequent fields.
            pub fn first(self: *Self) []const T {
                assert(self.index.? == self.buffer.len);
                return self.next().?;
            }

            /// Returns a slice of the next field, or null if splitting is complete.
            pub fn next(self: *Self) ?[]const T {
                const end = self.index orelse return null;
                const start = if (switch (delimiter_type) {
                    .sequence => lastIndexOf(T, self.buffer[0..end], self.delimiter),
                    .any => lastIndexOfAny(T, self.buffer[0..end], self.delimiter),
                    .scalar => lastIndexOfScalar(T, self.buffer[0..end], self.delimiter),
                }) |delim_start| blk: {
                    self.index = delim_start;
                    break :blk delim_start + switch (delimiter_type) {
                        .sequence => self.delimiter.len,
                        .any, .scalar => 1,
                    };
                } else blk: {
                    self.index = null;
                    break :blk 0;
                };
                return self.buffer[start..end];
            }

            /// Returns a slice of the remaining bytes. Does not affect iterator state.
            pub fn rest(self: Self) []const T {
                const end = self.index orelse 0;
                return self.buffer[0..end];
            }

            /// Resets the iterator to the initial slice.
            pub fn reset(self: *Self) void {
                self.index = self.buffer.len;
            }
        };
    }

    /// Naively combines a series of slices with a separator.
    /// Allocates memory for the result, which must be freed by the caller.
    pub fn join(allocator: Allocator, separator: []const u8, slices: []const []const u8) ![]u8 {
        return joinMaybeZ(allocator, separator, slices, false);
    }

    /// Naively combines a series of slices with a separator and null terminator.
    /// Allocates memory for the result, which must be freed by the caller.
    pub fn joinZ(allocator: Allocator, separator: []const u8, slices: []const []const u8) ![:0]u8 {
        const out = try joinMaybeZ(allocator, separator, slices, true);
        return out[0 .. out.len - 1 :0];
    }

    fn joinMaybeZ(allocator: Allocator, separator: []const u8, slices: []const []const u8, zero: bool) ![]u8 {
        if (slices.len == 0) return if (zero) try allocator.dupe(u8, &[1]u8{0}) else &[0]u8{};

        const total_len = blk: {
            var sum: usize = separator.len * (slices.len - 1);
            for (slices) |slice| sum += slice.len;
            if (zero) sum += 1;
            break :blk sum;
        };

        const buf = try allocator.alloc(u8, total_len);
        errdefer allocator.free(buf);

        copy(u8, buf, slices[0]);
        var buf_index: usize = slices[0].len;
        for (slices[1..]) |slice| {
            copy(u8, buf[buf_index..], separator);
            buf_index += separator.len;
            copy(u8, buf[buf_index..], slice);
            buf_index += slice.len;
        }

        if (zero) buf[buf.len - 1] = 0;

        // No need for shrink since buf is exactly the correct size.

        return buf;
    }

    test "join" {
        {
            const str = try join(testing.allocator, ",", &[_][]const u8{});
            defer testing.allocator.free(str);
            try testing.expect(eql(u8, str, ""));
        }
        {
            const str = try join(testing.allocator, ",", &[_][]const u8{ "a", "b", "c" });
            defer testing.allocator.free(str);
            try testing.expect(eql(u8, str, "a,b,c"));
        }
        {
            const str = try join(testing.allocator, ",", &[_][]const u8{"a"});
            defer testing.allocator.free(str);
            try testing.expect(eql(u8, str, "a"));
        }
        {
            const str = try join(testing.allocator, ",", &[_][]const u8{ "a", "", "b", "", "c" });
            defer testing.allocator.free(str);
            try testing.expect(eql(u8, str, "a,,b,,c"));
        }
    }

    test "joinZ" {
        {
            const str = try joinZ(testing.allocator, ",", &[_][]const u8{});
            defer testing.allocator.free(str);
            try testing.expect(eql(u8, str, ""));
            try testing.expectEqual(str[str.len], 0);
        }
        {
            const str = try joinZ(testing.allocator, ",", &[_][]const u8{ "a", "b", "c" });
            defer testing.allocator.free(str);
            try testing.expect(eql(u8, str, "a,b,c"));
            try testing.expectEqual(str[str.len], 0);
        }
        {
            const str = try joinZ(testing.allocator, ",", &[_][]const u8{"a"});
            defer testing.allocator.free(str);
            try testing.expect(eql(u8, str, "a"));
            try testing.expectEqual(str[str.len], 0);
        }
        {
            const str = try joinZ(testing.allocator, ",", &[_][]const u8{ "a", "", "b", "", "c" });
            defer testing.allocator.free(str);
            try testing.expect(eql(u8, str, "a,,b,,c"));
            try testing.expectEqual(str[str.len], 0);
        }
    }

    /// Copies each T from slices into a new slice that exactly holds all the elements.
    pub fn concat(allocator: Allocator, comptime T: type, slices: []const []const T) ![]T {
        return concatMaybeSentinel(allocator, T, slices, null);
    }

    /// Copies each T from slices into a new slice that exactly holds all the elements.
    pub fn concatWithSentinel(allocator: Allocator, comptime T: type, slices: []const []const T, comptime s: T) ![:s]T {
        const ret = try concatMaybeSentinel(allocator, T, slices, s);
        return ret[0 .. ret.len - 1 :s];
    }

    /// Copies each T from slices into a new slice that exactly holds all the elements as well as the sentinel.
    pub fn concatMaybeSentinel(allocator: Allocator, comptime T: type, slices: []const []const T, comptime s: ?T) ![]T {
        if (slices.len == 0) return if (s) |sentinel| try allocator.dupe(T, &[1]T{sentinel}) else &[0]T{};

        const total_len = blk: {
            var sum: usize = 0;
            for (slices) |slice| {
                sum += slice.len;
            }

            if (s) |_| {
                sum += 1;
            }

            break :blk sum;
        };

        const buf = try allocator.alloc(T, total_len);
        errdefer allocator.free(buf);

        var buf_index: usize = 0;
        for (slices) |slice| {
            copy(T, buf[buf_index..], slice);
            buf_index += slice.len;
        }

        if (s) |sentinel| {
            buf[buf.len - 1] = sentinel;
        }

        // No need for shrink since buf is exactly the correct size.

        return buf;
    }

    test "concat" {
        {
            const str = try concat(testing.allocator, u8, &[_][]const u8{ "abc", "def", "ghi" });
            defer testing.allocator.free(str);
            try testing.expect(eql(u8, str, "abcdefghi"));
        }
        {
            const str = try concat(testing.allocator, u32, &[_][]const u32{
                &[_]u32{ 0, 1 },
                &[_]u32{ 2, 3, 4 },
                &[_]u32{},
                &[_]u32{5},
            });
            defer testing.allocator.free(str);
            try testing.expect(eql(u32, str, &[_]u32{ 0, 1, 2, 3, 4, 5 }));
        }
        {
            const str = try concatWithSentinel(testing.allocator, u8, &[_][]const u8{ "abc", "def", "ghi" }, 0);
            defer testing.allocator.free(str);
            try testing.expectEqualSentinel(u8, 0, str, "abcdefghi");
        }
        {
            const slice = try concatWithSentinel(testing.allocator, u8, &[_][]const u8{}, 0);
            defer testing.allocator.free(slice);
            try testing.expectEqualSentinel(u8, 0, slice, &[_:0]u8{});
        }
        {
            const slice = try concatWithSentinel(testing.allocator, u32, &[_][]const u32{
                &[_]u32{ 0, 1 },
                &[_]u32{ 2, 3, 4 },
                &[_]u32{},
                &[_]u32{5},
            }, 2);
            defer testing.allocator.free(slice);
            try testing.expectEqualSentinel(u32, 2, slice, &[_:2]u32{ 0, 1, 2, 3, 4, 5 });
        }
    }

    test "testStringEquality" {
        try testing.expect(eql(u8, "abcd", "abcd"));
        try testing.expect(!eql(u8, "abcdef", "abZdef"));
        try testing.expect(!eql(u8, "abcdefg", "abcdef"));
    }

    test "testReadInt" {
        try testReadIntImpl();
        try comptime testReadIntImpl();
    }
    fn testReadIntImpl() !void {
        {
            const bytes = [_]u8{
                0x12,
                0x34,
                0x56,
                0x78,
            };
            try testing.expect(readInt(u32, &bytes, Endian.Big) == 0x12345678);
            try testing.expect(readIntBig(u32, &bytes) == 0x12345678);
            try testing.expect(readIntBig(i32, &bytes) == 0x12345678);
            try testing.expect(readInt(u32, &bytes, Endian.Little) == 0x78563412);
            try testing.expect(readIntLittle(u32, &bytes) == 0x78563412);
            try testing.expect(readIntLittle(i32, &bytes) == 0x78563412);
        }
        {
            const buf = [_]u8{
                0x00,
                0x00,
                0x12,
                0x34,
            };
            const answer = readInt(u32, &buf, Endian.Big);
            try testing.expect(answer == 0x00001234);
        }
        {
            const buf = [_]u8{
                0x12,
                0x34,
                0x00,
                0x00,
            };
            const answer = readInt(u32, &buf, Endian.Little);
            try testing.expect(answer == 0x00003412);
        }
        {
            const bytes = [_]u8{
                0xff,
                0xfe,
            };
            try testing.expect(readIntBig(u16, &bytes) == 0xfffe);
            try testing.expect(readIntBig(i16, &bytes) == -0x0002);
            try testing.expect(readIntLittle(u16, &bytes) == 0xfeff);
            try testing.expect(readIntLittle(i16, &bytes) == -0x0101);
        }
    }

    test writeIntSlice {
        try testWriteIntImpl();
        try comptime testWriteIntImpl();
    }
    fn testWriteIntImpl() !void {
        var bytes: [8]u8 = undefined;

        writeIntSlice(u0, bytes[0..], 0, Endian.Big);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x00, 0x00, 0x00, 0x00,
            0x00, 0x00, 0x00, 0x00,
        }));

        writeIntSlice(u0, bytes[0..], 0, Endian.Little);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x00, 0x00, 0x00, 0x00,
            0x00, 0x00, 0x00, 0x00,
        }));

        writeIntSlice(u64, bytes[0..], 0x12345678CAFEBABE, Endian.Big);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x12,
            0x34,
            0x56,
            0x78,
            0xCA,
            0xFE,
            0xBA,
            0xBE,
        }));

        writeIntSlice(u64, bytes[0..], 0xBEBAFECA78563412, Endian.Little);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x12,
            0x34,
            0x56,
            0x78,
            0xCA,
            0xFE,
            0xBA,
            0xBE,
        }));

        writeIntSlice(u32, bytes[0..], 0x12345678, Endian.Big);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x00,
            0x00,
            0x00,
            0x00,
            0x12,
            0x34,
            0x56,
            0x78,
        }));

        writeIntSlice(u32, bytes[0..], 0x78563412, Endian.Little);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x12,
            0x34,
            0x56,
            0x78,
            0x00,
            0x00,
            0x00,
            0x00,
        }));

        writeIntSlice(u16, bytes[0..], 0x1234, Endian.Big);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x00,
            0x00,
            0x00,
            0x00,
            0x00,
            0x00,
            0x12,
            0x34,
        }));

        writeIntSlice(u16, bytes[0..], 0x1234, Endian.Little);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x34,
            0x12,
            0x00,
            0x00,
            0x00,
            0x00,
            0x00,
            0x00,
        }));

        writeIntSlice(i16, bytes[0..], @as(i16, -21555), Endian.Little);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0xCD,
            0xAB,
            0x00,
            0x00,
            0x00,
            0x00,
            0x00,
            0x00,
        }));

        writeIntSlice(i16, bytes[0..], @as(i16, -21555), Endian.Big);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x00,
            0x00,
            0x00,
            0x00,
            0x00,
            0x00,
            0xAB,
            0xCD,
        }));

        writeIntSlice(u8, bytes[0..], 0x12, Endian.Big);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x00, 0x00, 0x00, 0x00,
            0x00, 0x00, 0x00, 0x12,
        }));

        writeIntSlice(u8, bytes[0..], 0x12, Endian.Little);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x12, 0x00, 0x00, 0x00,
            0x00, 0x00, 0x00, 0x00,
        }));

        writeIntSlice(i8, bytes[0..], -1, Endian.Big);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0x00, 0x00, 0x00, 0x00,
            0x00, 0x00, 0x00, 0xff,
        }));

        writeIntSlice(i8, bytes[0..], -1, Endian.Little);
        try testing.expect(eql(u8, &bytes, &[_]u8{
            0xff, 0x00, 0x00, 0x00,
            0x00, 0x00, 0x00, 0x00,
        }));
    }

    /// Returns the smallest number in a slice. O(n).
    /// `slice` must not be empty.
    pub fn min(comptime T: type, slice: []const T) T {
        assert(slice.len > 0);
        var best = slice[0];
        for (slice[1..]) |item| {
            best = @min(best, item);
        }
        return best;
    }

    test "min" {
        try testing.expectEqual(min(u8, "abcdefg"), 'a');
        try testing.expectEqual(min(u8, "bcdefga"), 'a');
        try testing.expectEqual(min(u8, "a"), 'a');
    }

    /// Returns the largest number in a slice. O(n).
    /// `slice` must not be empty.
    pub fn max(comptime T: type, slice: []const T) T {
        assert(slice.len > 0);
        var best = slice[0];
        for (slice[1..]) |item| {
            best = @max(best, item);
        }
        return best;
    }

    test "max" {
        try testing.expectEqual(max(u8, "abcdefg"), 'g');
        try testing.expectEqual(max(u8, "gabcdef"), 'g');
        try testing.expectEqual(max(u8, "g"), 'g');
    }

    /// Finds the smallest and largest number in a slice. O(n).
    /// Returns an anonymous struct with the fields `min` and `max`.
    /// `slice` must not be empty.
    pub fn minMax(comptime T: type, slice: []const T) struct { min: T, max: T } {
        assert(slice.len > 0);
        var minVal = slice[0];
        var maxVal = slice[0];
        for (slice[1..]) |item| {
            minVal = @min(minVal, item);
            maxVal = @max(maxVal, item);
        }
        return .{ .min = minVal, .max = maxVal };
    }

    test "minMax" {
        try testing.expectEqual(minMax(u8, "abcdefg"), .{ .min = 'a', .max = 'g' });
        try testing.expectEqual(minMax(u8, "bcdefga"), .{ .min = 'a', .max = 'g' });
        try testing.expectEqual(minMax(u8, "a"), .{ .min = 'a', .max = 'a' });
    }

    /// Returns the index of the smallest number in a slice. O(n).
    /// `slice` must not be empty.
    pub fn indexOfMin(comptime T: type, slice: []const T) usize {
        assert(slice.len > 0);
        var best = slice[0];
        var index: usize = 0;
        for (slice[1..], 0..) |item, i| {
            if (item < best) {
                best = item;
                index = i + 1;
            }
        }
        return index;
    }

    test "indexOfMin" {
        try testing.expectEqual(indexOfMin(u8, "abcdefg"), 0);
        try testing.expectEqual(indexOfMin(u8, "bcdefga"), 6);
        try testing.expectEqual(indexOfMin(u8, "a"), 0);
    }

    /// Returns the index of the largest number in a slice. O(n).
    /// `slice` must not be empty.
    pub fn indexOfMax(comptime T: type, slice: []const T) usize {
        assert(slice.len > 0);
        var best = slice[0];
        var index: usize = 0;
        for (slice[1..], 0..) |item, i| {
            if (item > best) {
                best = item;
                index = i + 1;
            }
        }
        return index;
    }

    test "indexOfMax" {
        try testing.expectEqual(indexOfMax(u8, "abcdefg"), 6);
        try testing.expectEqual(indexOfMax(u8, "gabcdef"), 0);
        try testing.expectEqual(indexOfMax(u8, "a"), 0);
    }

    /// Finds the indices of the smallest and largest number in a slice. O(n).
    /// Returns an anonymous struct with the fields `index_min` and `index_max`.
    /// `slice` must not be empty.
    pub fn indexOfMinMax(comptime T: type, slice: []const T) struct { index_min: usize, index_max: usize } {
        assert(slice.len > 0);
        var minVal = slice[0];
        var maxVal = slice[0];
        var minIdx: usize = 0;
        var maxIdx: usize = 0;
        for (slice[1..], 0..) |item, i| {
            if (item < minVal) {
                minVal = item;
                minIdx = i + 1;
            }
            if (item > maxVal) {
                maxVal = item;
                maxIdx = i + 1;
            }
        }
        return .{ .index_min = minIdx, .index_max = maxIdx };
    }

    test "indexOfMinMax" {
        try testing.expectEqual(indexOfMinMax(u8, "abcdefg"), .{ .index_min = 0, .index_max = 6 });
        try testing.expectEqual(indexOfMinMax(u8, "gabcdef"), .{ .index_min = 1, .index_max = 0 });
        try testing.expectEqual(indexOfMinMax(u8, "a"), .{ .index_min = 0, .index_max = 0 });
    }

    pub fn swap(comptime T: type, a: *T, b: *T) void {
        const tmp = a.*;
        a.* = b.*;
        b.* = tmp;
    }

    /// In-place order reversal of a slice
    pub fn reverse(comptime T: type, items: []T) void {
        var i: usize = 0;
        const end = items.len / 2;
        while (i < end) : (i += 1) {
            swap(T, &items[i], &items[items.len - i - 1]);
        }
    }

    test "reverse" {
        var arr = [_]i32{ 5, 3, 1, 2, 4 };
        reverse(i32, arr[0..]);

        try testing.expect(eql(i32, &arr, &[_]i32{ 4, 2, 1, 3, 5 }));
    }

    fn ReverseIterator(comptime T: type) type {
        const Pointer = blk: {
            switch (@typeInfo(T)) {
                .Pointer => |ptr_info| switch (ptr_info.size) {
                    .One => switch (@typeInfo(ptr_info.child)) {
                        .Array => |array_info| {
                            var new_ptr_info = ptr_info;
                            new_ptr_info.size = .Many;
                            new_ptr_info.child = array_info.child;
                            new_ptr_info.sentinel = array_info.sentinel;
                            break :blk @Type(.{ .Pointer = new_ptr_info });
                        },
                        else => {},
                    },
                    .Slice => {
                        var new_ptr_info = ptr_info;
                        new_ptr_info.size = .Many;
                        break :blk @Type(.{ .Pointer = new_ptr_info });
                    },
                    else => {},
                },
                else => {},
            }
            @compileError("expected slice or pointer to array, found '" ++ @typeName(T) ++ "'");
        };
        const Element = std.meta.Elem(Pointer);
        const ElementPointer = @TypeOf(&@as(Pointer, undefined)[0]);
        return struct {
            ptr: Pointer,
            index: usize,
            pub fn next(self: *@This()) ?Element {
                if (self.index == 0) return null;
                self.index -= 1;
                return self.ptr[self.index];
            }
            pub fn nextPtr(self: *@This()) ?ElementPointer {
                if (self.index == 0) return null;
                self.index -= 1;
                return &self.ptr[self.index];
            }
        };
    }

    /// Iterates over a slice in reverse.
    pub fn reverseIterator(slice: anytype) ReverseIterator(@TypeOf(slice)) {
        const T = @TypeOf(slice);
        if (comptime trait.isPtrTo(.Array)(T)) {
            return .{ .ptr = slice, .index = slice.len };
        } else {
            comptime assert(trait.isSlice(T));
            return .{ .ptr = slice.ptr, .index = slice.len };
        }
    }

    test "reverseIterator" {
        {
            var it = reverseIterator("abc");
            try testing.expectEqual(@as(?u8, 'c'), it.next());
            try testing.expectEqual(@as(?u8, 'b'), it.next());
            try testing.expectEqual(@as(?u8, 'a'), it.next());
            try testing.expectEqual(@as(?u8, null), it.next());
        }
        {
            var array = [2]i32{ 3, 7 };
            const slice: []const i32 = &array;
            var it = reverseIterator(slice);
            try testing.expectEqual(@as(?i32, 7), it.next());
            try testing.expectEqual(@as(?i32, 3), it.next());
            try testing.expectEqual(@as(?i32, null), it.next());

            it = reverseIterator(slice);
            try testing.expect(trait.isConstPtr(@TypeOf(it.nextPtr().?)));
            try testing.expectEqual(@as(?i32, 7), it.nextPtr().?.*);
            try testing.expectEqual(@as(?i32, 3), it.nextPtr().?.*);
            try testing.expectEqual(@as(?*const i32, null), it.nextPtr());

            var mut_slice: []i32 = &array;
            var mut_it = reverseIterator(mut_slice);
            mut_it.nextPtr().?.* += 1;
            mut_it.nextPtr().?.* += 2;
            try testing.expectEqual([2]i32{ 5, 8 }, array);
        }
        {
            var array = [2]i32{ 3, 7 };
            const ptr_to_array: *const [2]i32 = &array;
            var it = reverseIterator(ptr_to_array);
            try testing.expectEqual(@as(?i32, 7), it.next());
            try testing.expectEqual(@as(?i32, 3), it.next());
            try testing.expectEqual(@as(?i32, null), it.next());

            it = reverseIterator(ptr_to_array);
            try testing.expect(trait.isConstPtr(@TypeOf(it.nextPtr().?)));
            try testing.expectEqual(@as(?i32, 7), it.nextPtr().?.*);
            try testing.expectEqual(@as(?i32, 3), it.nextPtr().?.*);
            try testing.expectEqual(@as(?*const i32, null), it.nextPtr());

            var mut_ptr_to_array: *[2]i32 = &array;
            var mut_it = reverseIterator(mut_ptr_to_array);
            mut_it.nextPtr().?.* += 1;
            mut_it.nextPtr().?.* += 2;
            try testing.expectEqual([2]i32{ 5, 8 }, array);
        }
    }

    /// In-place rotation of the values in an array ([0 1 2 3] becomes [1 2 3 0] if we rotate by 1)
    /// Assumes 0 <= amount <= items.len
    pub fn rotate(comptime T: type, items: []T, amount: usize) void {
        reverse(T, items[0..amount]);
        reverse(T, items[amount..]);
        reverse(T, items);
    }

    test "rotate" {
        var arr = [_]i32{ 5, 3, 1, 2, 4 };
        rotate(i32, arr[0..], 2);

        try testing.expect(eql(i32, &arr, &[_]i32{ 1, 2, 4, 5, 3 }));
    }

    /// Replace needle with replacement as many times as possible, writing to an output buffer which is assumed to be of
    /// appropriate size. Use replacementSize to calculate an appropriate buffer size.
    /// The needle must not be empty.
    /// Returns the number of replacements made.
    pub fn replace(comptime T: type, input: []const T, needle: []const T, replacement: []const T, output: []T) usize {
        // Empty needle will loop until output buffer overflows.

        assert(needle.len > 0);

        var i: usize = 0;
        var slide: usize = 0;
        var replacements: usize = 0;
        while (slide < input.len) {
            if (mem.startsWith(T, input[slide..], needle)) {
                @memcpy(output[i..][0..replacement.len], replacement);
                i += replacement.len;
                slide += needle.len;
                replacements += 1;
            } else {
                output[i] = input[slide];
                i += 1;
                slide += 1;
            }
        }

        return replacements;
    }

    test "replace" {
        var output: [29]u8 = undefined;
        var replacements = replace(u8, "All your base are belong to us", "base", "Zig", output[0..]);
        var expected: []const u8 = "All your Zig are belong to us";
        try testing.expect(replacements == 1);
        try testing.expectEqualStrings(expected, output[0..expected.len]);

        replacements = replace(u8, "Favor reading code over writing code.", "code", "", output[0..]);
        expected = "Favor reading  over writing .";
        try testing.expect(replacements == 2);
        try testing.expectEqualStrings(expected, output[0..expected.len]);

        // Empty needle is not allowed but input may be empty.

        replacements = replace(u8, "", "x", "y", output[0..0]);
        expected = "";
        try testing.expect(replacements == 0);
        try testing.expectEqualStrings(expected, output[0..expected.len]);

        // Adjacent replacements.

        replacements = replace(u8, "\\n\\n", "\\n", "\n", output[0..]);
        expected = "\n\n";
        try testing.expect(replacements == 2);
        try testing.expectEqualStrings(expected, output[0..expected.len]);

        replacements = replace(u8, "abbba", "b", "cd", output[0..]);
        expected = "acdcdcda";
        try testing.expect(replacements == 3);
        try testing.expectEqualStrings(expected, output[0..expected.len]);
    }

    /// Replace all occurrences of `needle` with `replacement`.
    pub fn replaceScalar(comptime T: type, slice: []T, needle: T, replacement: T) void {
        for (slice, 0..) |e, i| {
            if (e == needle) {
                slice[i] = replacement;
            }
        }
    }

    /// Collapse consecutive duplicate elements into one entry.
    pub fn collapseRepeatsLen(comptime T: type, slice: []T, elem: T) usize {
        if (slice.len == 0) return 0;
        var write_idx: usize = 1;
        var read_idx: usize = 1;
        while (read_idx < slice.len) : (read_idx += 1) {
            if (slice[read_idx - 1] != elem or slice[read_idx] != elem) {
                slice[write_idx] = slice[read_idx];
                write_idx += 1;
            }
        }
        return write_idx;
    }

    /// Collapse consecutive duplicate elements into one entry.
    pub fn collapseRepeats(comptime T: type, slice: []T, elem: T) []T {
        return slice[0..collapseRepeatsLen(T, slice, elem)];
    }

    fn testCollapseRepeats(str: []const u8, elem: u8, expected: []const u8) !void {
        const mutable = try std.testing.allocator.dupe(u8, str);
        defer std.testing.allocator.free(mutable);
        try testing.expect(std.mem.eql(u8, collapseRepeats(u8, mutable, elem), expected));
    }
    test "collapseRepeats" {
        try testCollapseRepeats("", '/', "");
        try testCollapseRepeats("a", '/', "a");
        try testCollapseRepeats("/", '/', "/");
        try testCollapseRepeats("//", '/', "/");
        try testCollapseRepeats("/a", '/', "/a");
        try testCollapseRepeats("//a", '/', "/a");
        try testCollapseRepeats("a/", '/', "a/");
        try testCollapseRepeats("a//", '/', "a/");
        try testCollapseRepeats("a/a", '/', "a/a");
        try testCollapseRepeats("a//a", '/', "a/a");
        try testCollapseRepeats("//a///a////", '/', "/a/a/");
    }

    /// Calculate the size needed in an output buffer to perform a replacement.
    /// The needle must not be empty.
    pub fn replacementSize(comptime T: type, input: []const T, needle: []const T, replacement: []const T) usize {
        // Empty needle will loop forever.

        assert(needle.len > 0);

        var i: usize = 0;
        var size: usize = input.len;
        while (i < input.len) {
            if (mem.startsWith(T, input[i..], needle)) {
                size = size - needle.len + replacement.len;
                i += needle.len;
            } else {
                i += 1;
            }
        }

        return size;
    }

    test "replacementSize" {
        try testing.expect(replacementSize(u8, "All your base are belong to us", "base", "Zig") == 29);
        try testing.expect(replacementSize(u8, "Favor reading code over writing code.", "code", "") == 29);
        try testing.expect(replacementSize(u8, "Only one obvious way to do things.", "things.", "things in Zig.") == 41);

        // Empty needle is not allowed but input may be empty.

        try testing.expect(replacementSize(u8, "", "x", "y") == 0);

        // Adjacent replacements.

        try testing.expect(replacementSize(u8, "\\n\\n", "\\n", "\n") == 2);
        try testing.expect(replacementSize(u8, "abbba", "b", "cd") == 8);
    }

    /// Perform a replacement on an allocated buffer of pre-determined size. Caller must free returned memory.
    pub fn replaceOwned(comptime T: type, allocator: Allocator, input: []const T, needle: []const T, replacement: []const T) Allocator.Error![]T {
        var output = try allocator.alloc(T, replacementSize(T, input, needle, replacement));
        _ = replace(T, input, needle, replacement, output);
        return output;
    }

    test "replaceOwned" {
        const gpa = std.testing.allocator;

        const base_replace = replaceOwned(u8, gpa, "All your base are belong to us", "base", "Zig") catch @panic("out of memory");
        defer gpa.free(base_replace);
        try testing.expect(eql(u8, base_replace, "All your Zig are belong to us"));

        const zen_replace = replaceOwned(u8, gpa, "Favor reading code over writing code.", " code", "") catch @panic("out of memory");
        defer gpa.free(zen_replace);
        try testing.expect(eql(u8, zen_replace, "Favor reading over writing."));
    }

    /// Converts a little-endian integer to host endianness.
    pub fn littleToNative(comptime T: type, x: T) T {
        return switch (native_endian) {
            .Little => x,
            .Big => @byteSwap(x),
        };
    }

    /// Converts a big-endian integer to host endianness.
    pub fn bigToNative(comptime T: type, x: T) T {
        return switch (native_endian) {
            .Little => @byteSwap(x),
            .Big => x,
        };
    }

    /// Converts an integer from specified endianness to host endianness.
    pub fn toNative(comptime T: type, x: T, endianness_of_x: Endian) T {
        return switch (endianness_of_x) {
            .Little => littleToNative(T, x),
            .Big => bigToNative(T, x),
        };
    }

    /// Converts an integer which has host endianness to the desired endianness.
    pub fn nativeTo(comptime T: type, x: T, desired_endianness: Endian) T {
        return switch (desired_endianness) {
            .Little => nativeToLittle(T, x),
            .Big => nativeToBig(T, x),
        };
    }

    /// Converts an integer which has host endianness to little endian.
    pub fn nativeToLittle(comptime T: type, x: T) T {
        return switch (native_endian) {
            .Little => x,
            .Big => @byteSwap(x),
        };
    }

    /// Converts an integer which has host endianness to big endian.
    pub fn nativeToBig(comptime T: type, x: T) T {
        return switch (native_endian) {
            .Little => @byteSwap(x),
            .Big => x,
        };
    }

    /// Returns the number of elements that, if added to the given pointer, align it
    /// to a multiple of the given quantity, or `null` if one of the following
    /// conditions is met:
    /// - The aligned pointer would not fit the address space,
    /// - The delta required to align the pointer is not a multiple of the pointee's
    ///   type.
    pub fn alignPointerOffset(ptr: anytype, align_to: usize) ?usize {
        assert(isValidAlign(align_to));

        const T = @TypeOf(ptr);
        const info = @typeInfo(T);
        if (info != .Pointer or info.Pointer.size != .Many)
            @compileError("expected many item pointer, got " ++ @typeName(T));

        // Do nothing if the pointer is already well-aligned.

        if (align_to <= info.Pointer.alignment)
            return 0;

        // Calculate the aligned base address with an eye out for overflow.

        const addr = @intFromPtr(ptr);
        var ov = @addWithOverflow(addr, align_to - 1);
        if (ov[1] != 0) return null;
        ov[0] &= ~@as(usize, align_to - 1);

        // The delta is expressed in terms of bytes, turn it into a number of child

        // type elements.

        const delta = ov[0] - addr;
        const pointee_size = @sizeOf(info.Pointer.child);
        if (delta % pointee_size != 0) return null;
        return delta / pointee_size;
    }

    /// Aligns a given pointer value to a specified alignment factor.
    /// Returns an aligned pointer or null if one of the following conditions is
    /// met:
    /// - The aligned pointer would not fit the address space,
    /// - The delta required to align the pointer is not a multiple of the pointee's
    ///   type.
    pub fn alignPointer(ptr: anytype, align_to: usize) ?@TypeOf(ptr) {
        const adjust_off = alignPointerOffset(ptr, align_to) orelse return null;
        // Avoid the use of ptrFromInt to avoid losing the pointer provenance info.

        return @alignCast(ptr + adjust_off);
    }

    test "alignPointer" {
        const S = struct {
            fn checkAlign(comptime T: type, base: usize, align_to: usize, expected: usize) !void {
                var ptr = @as(T, @ptrFromInt(base));
                var aligned = alignPointer(ptr, align_to);
                try testing.expectEqual(expected, @intFromPtr(aligned));
            }
        };

        try S.checkAlign([*]u8, 0x123, 0x200, 0x200);
        try S.checkAlign([*]align(4) u8, 0x10, 2, 0x10);
        try S.checkAlign([*]u32, 0x10, 2, 0x10);
        try S.checkAlign([*]u32, 0x4, 16, 0x10);
        // Misaligned.

        try S.checkAlign([*]align(1) u32, 0x3, 2, 0);
        // Overflow.

        try S.checkAlign([*]u32, math.maxInt(usize) - 3, 8, 0);
    }

    fn CopyPtrAttrs(
        comptime source: type,
        comptime size: std.builtin.Type.Pointer.Size,
        comptime child: type,
    ) type {
        const info = @typeInfo(source).Pointer;
        return @Type(.{
            .Pointer = .{
                .size = size,
                .is_const = info.is_const,
                .is_volatile = info.is_volatile,
                .is_allowzero = info.is_allowzero,
                .alignment = info.alignment,
                .address_space = info.address_space,
                .child = child,
                .sentinel = null,
            },
        });
    }

    fn AsBytesReturnType(comptime P: type) type {
        if (!trait.isSingleItemPtr(P))
            @compileError("expected single item pointer, passed " ++ @typeName(P));

        const size = @sizeOf(meta.Child(P));

        return CopyPtrAttrs(P, .One, [size]u8);
    }

    /// Given a pointer to a single item, returns a slice of the underlying bytes, preserving pointer attributes.
    pub fn asBytes(ptr: anytype) AsBytesReturnType(@TypeOf(ptr)) {
        return @ptrCast(@alignCast(ptr));
    }

    test "asBytes" {
        const deadbeef = @as(u32, 0xDEADBEEF);
        const deadbeef_bytes = switch (native_endian) {
            .Big => "\xDE\xAD\xBE\xEF",
            .Little => "\xEF\xBE\xAD\xDE",
        };

        try testing.expect(eql(u8, asBytes(&deadbeef), deadbeef_bytes));

        var codeface = @as(u32, 0xC0DEFACE);
        for (asBytes(&codeface)) |*b|
            b.* = 0;
        try testing.expect(codeface == 0);

        const S = packed struct {
            a: u8,
            b: u8,
            c: u8,
            d: u8,
        };

        const inst = S{
            .a = 0xBE,
            .b = 0xEF,
            .c = 0xDE,
            .d = 0xA1,
        };
        switch (native_endian) {
            .Little => {
                try testing.expect(eql(u8, asBytes(&inst), "\xBE\xEF\xDE\xA1"));
            },
            .Big => {
                try testing.expect(eql(u8, asBytes(&inst), "\xA1\xDE\xEF\xBE"));
            },
        }

        const ZST = struct {};
        const zero = ZST{};
        try testing.expect(eql(u8, asBytes(&zero), ""));
    }

    test "asBytes preserves pointer attributes" {
        const inArr: u32 align(16) = 0xDEADBEEF;
        const inPtr = @as(*align(16) const volatile u32, @ptrCast(&inArr));
        const outSlice = asBytes(inPtr);

        const in = @typeInfo(@TypeOf(inPtr)).Pointer;
        const out = @typeInfo(@TypeOf(outSlice)).Pointer;

        try testing.expectEqual(in.is_const, out.is_const);
        try testing.expectEqual(in.is_volatile, out.is_volatile);
        try testing.expectEqual(in.is_allowzero, out.is_allowzero);
        try testing.expectEqual(in.alignment, out.alignment);
    }

    /// Given any value, returns a copy of its bytes in an array.
    pub fn toBytes(value: anytype) [@sizeOf(@TypeOf(value))]u8 {
        return asBytes(&value).*;
    }

    test "toBytes" {
        var my_bytes = toBytes(@as(u32, 0x12345678));
        switch (native_endian) {
            .Big => try testing.expect(eql(u8, &my_bytes, "\x12\x34\x56\x78")),
            .Little => try testing.expect(eql(u8, &my_bytes, "\x78\x56\x34\x12")),
        }

        my_bytes[0] = '\x99';
        switch (native_endian) {
            .Big => try testing.expect(eql(u8, &my_bytes, "\x99\x34\x56\x78")),
            .Little => try testing.expect(eql(u8, &my_bytes, "\x99\x56\x34\x12")),
        }
    }

    fn BytesAsValueReturnType(comptime T: type, comptime B: type) type {
        const size = @as(usize, @sizeOf(T));

        if (comptime !trait.is(.Pointer)(B) or
            (meta.Child(B) != [size]u8 and meta.Child(B) != [size:0]u8))
        {
            @compileError(std.fmt.comptimePrint("expected *[{}]u8, passed " ++ @typeName(B), .{size}));
        }

        return CopyPtrAttrs(B, .One, T);
    }

    /// Given a pointer to an array of bytes, returns a pointer to a value of the specified type
    /// backed by those bytes, preserving pointer attributes.
    pub fn bytesAsValue(comptime T: type, bytes: anytype) BytesAsValueReturnType(T, @TypeOf(bytes)) {
        return @as(BytesAsValueReturnType(T, @TypeOf(bytes)), @ptrCast(bytes));
    }

    test "bytesAsValue" {
        const deadbeef = @as(u32, 0xDEADBEEF);
        const deadbeef_bytes = switch (native_endian) {
            .Big => "\xDE\xAD\xBE\xEF",
            .Little => "\xEF\xBE\xAD\xDE",
        };

        try testing.expect(deadbeef == bytesAsValue(u32, deadbeef_bytes).*);

        var codeface_bytes: [4]u8 = switch (native_endian) {
            .Big => "\xC0\xDE\xFA\xCE",
            .Little => "\xCE\xFA\xDE\xC0",
        }.*;
        var codeface = bytesAsValue(u32, &codeface_bytes);
        try testing.expect(codeface.* == 0xC0DEFACE);
        codeface.* = 0;
        for (codeface_bytes) |b|
            try testing.expect(b == 0);

        const S = packed struct {
            a: u8,
            b: u8,
            c: u8,
            d: u8,
        };

        const inst = S{
            .a = 0xBE,
            .b = 0xEF,
            .c = 0xDE,
            .d = 0xA1,
        };
        const inst_bytes = switch (native_endian) {
            .Little => "\xBE\xEF\xDE\xA1",
            .Big => "\xA1\xDE\xEF\xBE",
        };
        const inst2 = bytesAsValue(S, inst_bytes);
        try testing.expect(meta.eql(inst, inst2.*));
    }

    test "bytesAsValue preserves pointer attributes" {
        const inArr align(16) = [4]u8{ 0xDE, 0xAD, 0xBE, 0xEF };
        const inSlice = @as(*align(16) const volatile [4]u8, @ptrCast(&inArr))[0..];
        const outPtr = bytesAsValue(u32, inSlice);

        const in = @typeInfo(@TypeOf(inSlice)).Pointer;
        const out = @typeInfo(@TypeOf(outPtr)).Pointer;

        try testing.expectEqual(in.is_const, out.is_const);
        try testing.expectEqual(in.is_volatile, out.is_volatile);
        try testing.expectEqual(in.is_allowzero, out.is_allowzero);
        try testing.expectEqual(in.alignment, out.alignment);
    }

    /// Given a pointer to an array of bytes, returns a value of the specified type backed by a
    /// copy of those bytes.
    pub fn bytesToValue(comptime T: type, bytes: anytype) T {
        return bytesAsValue(T, bytes).*;
    }
    test "bytesToValue" {
        const deadbeef_bytes = switch (native_endian) {
            .Big => "\xDE\xAD\xBE\xEF",
            .Little => "\xEF\xBE\xAD\xDE",
        };

        const deadbeef = bytesToValue(u32, deadbeef_bytes);
        try testing.expect(deadbeef == @as(u32, 0xDEADBEEF));
    }

    fn BytesAsSliceReturnType(comptime T: type, comptime bytesType: type) type {
        if (!(trait.isSlice(bytesType) or trait.isPtrTo(.Array)(bytesType)) or meta.Elem(bytesType) != u8) {
            @compileError("expected []u8 or *[_]u8, passed " ++ @typeName(bytesType));
        }

        if (trait.isPtrTo(.Array)(bytesType) and @typeInfo(meta.Child(bytesType)).Array.len % @sizeOf(T) != 0) {
            @compileError("number of bytes in " ++ @typeName(bytesType) ++ " is not divisible by size of " ++ @typeName(T));
        }

        return CopyPtrAttrs(bytesType, .Slice, T);
    }

    /// Given a slice of bytes, returns a slice of the specified type
    /// backed by those bytes, preserving pointer attributes.
    pub fn bytesAsSlice(comptime T: type, bytes: anytype) BytesAsSliceReturnType(T, @TypeOf(bytes)) {
        // let's not give an undefined pointer to @ptrCast

        // it may be equal to zero and fail a null check

        if (bytes.len == 0) {
            return &[0]T{};
        }

        const cast_target = CopyPtrAttrs(@TypeOf(bytes), .Many, T);

        return @as(cast_target, @ptrCast(bytes))[0..@divExact(bytes.len, @sizeOf(T))];
    }

    test "bytesAsSlice" {
        {
            const bytes = [_]u8{ 0xDE, 0xAD, 0xBE, 0xEF };
            const slice = bytesAsSlice(u16, bytes[0..]);
            try testing.expect(slice.len == 2);
            try testing.expect(bigToNative(u16, slice[0]) == 0xDEAD);
            try testing.expect(bigToNative(u16, slice[1]) == 0xBEEF);
        }
        {
            const bytes = [_]u8{ 0xDE, 0xAD, 0xBE, 0xEF };
            var runtime_zero: usize = 0;
            const slice = bytesAsSlice(u16, bytes[runtime_zero..]);
            try testing.expect(slice.len == 2);
            try testing.expect(bigToNative(u16, slice[0]) == 0xDEAD);
            try testing.expect(bigToNative(u16, slice[1]) == 0xBEEF);
        }
    }

    test "bytesAsSlice keeps pointer alignment" {
        {
            var bytes = [_]u8{ 0x01, 0x02, 0x03, 0x04 };
            const numbers = bytesAsSlice(u32, bytes[0..]);
            try comptime testing.expect(@TypeOf(numbers) == []align(@alignOf(@TypeOf(bytes))) u32);
        }
        {
            var bytes = [_]u8{ 0x01, 0x02, 0x03, 0x04 };
            var runtime_zero: usize = 0;
            const numbers = bytesAsSlice(u32, bytes[runtime_zero..]);
            try comptime testing.expect(@TypeOf(numbers) == []align(@alignOf(@TypeOf(bytes))) u32);
        }
    }

    test "bytesAsSlice on a packed struct" {
        const F = packed struct {
            a: u8,
        };

        var b = [1]u8{9};
        var f = bytesAsSlice(F, &b);
        try testing.expect(f[0].a == 9);
    }

    test "bytesAsSlice with specified alignment" {
        var bytes align(4) = [_]u8{
            0x33,
            0x33,
            0x33,
            0x33,
        };
        const slice: []u32 = std.mem.bytesAsSlice(u32, bytes[0..]);
        try testing.expect(slice[0] == 0x33333333);
    }

    test "bytesAsSlice preserves pointer attributes" {
        const inArr align(16) = [4]u8{ 0xDE, 0xAD, 0xBE, 0xEF };
        const inSlice = @as(*align(16) const volatile [4]u8, @ptrCast(&inArr))[0..];
        const outSlice = bytesAsSlice(u16, inSlice);

        const in = @typeInfo(@TypeOf(inSlice)).Pointer;
        const out = @typeInfo(@TypeOf(outSlice)).Pointer;

        try testing.expectEqual(in.is_const, out.is_const);
        try testing.expectEqual(in.is_volatile, out.is_volatile);
        try testing.expectEqual(in.is_allowzero, out.is_allowzero);
        try testing.expectEqual(in.alignment, out.alignment);
    }

    fn SliceAsBytesReturnType(comptime sliceType: type) type {
        if (!trait.isSlice(sliceType) and !trait.isPtrTo(.Array)(sliceType)) {
            @compileError("expected []T or *[_]T, passed " ++ @typeName(sliceType));
        }

        return CopyPtrAttrs(sliceType, .Slice, u8);
    }

    /// Given a slice, returns a slice of the underlying bytes, preserving pointer attributes.
    pub fn sliceAsBytes(slice: anytype) SliceAsBytesReturnType(@TypeOf(slice)) {
        const Slice = @TypeOf(slice);

        // let's not give an undefined pointer to @ptrCast

        // it may be equal to zero and fail a null check

        if (slice.len == 0 and comptime meta.sentinel(Slice) == null) {
            return &[0]u8{};
        }

        const cast_target = CopyPtrAttrs(Slice, .Many, u8);

        return @as(cast_target, @ptrCast(slice))[0 .. slice.len * @sizeOf(meta.Elem(Slice))];
    }

    test "sliceAsBytes" {
        const bytes = [_]u16{ 0xDEAD, 0xBEEF };
        const slice = sliceAsBytes(bytes[0..]);
        try testing.expect(slice.len == 4);
        try testing.expect(eql(u8, slice, switch (native_endian) {
            .Big => "\xDE\xAD\xBE\xEF",
            .Little => "\xAD\xDE\xEF\xBE",
        }));
    }

    test "sliceAsBytes with sentinel slice" {
        const empty_string: [:0]const u8 = "";
        const bytes = sliceAsBytes(empty_string);
        try testing.expect(bytes.len == 0);
    }

    test "sliceAsBytes packed struct at runtime and comptime" {
        const Foo = packed struct {
            a: u4,
            b: u4,
        };
        const S = struct {
            fn doTheTest() !void {
                var foo: Foo = undefined;
                var slice = sliceAsBytes(@as(*[1]Foo, &foo)[0..1]);
                slice[0] = 0x13;
                try testing.expect(foo.a == 0x3);
                try testing.expect(foo.b == 0x1);
            }
        };
        try S.doTheTest();
        try comptime S.doTheTest();
    }

    test "sliceAsBytes and bytesAsSlice back" {
        try testing.expect(@sizeOf(i32) == 4);

        var big_thing_array = [_]i32{ 1, 2, 3, 4 };
        const big_thing_slice: []i32 = big_thing_array[0..];

        const bytes = sliceAsBytes(big_thing_slice);
        try testing.expect(bytes.len == 4 * 4);

        bytes[4] = 0;
        bytes[5] = 0;
        bytes[6] = 0;
        bytes[7] = 0;
        try testing.expect(big_thing_slice[1] == 0);

        const big_thing_again = bytesAsSlice(i32, bytes);
        try testing.expect(big_thing_again[2] == 3);

        big_thing_again[2] = -1;
        try testing.expect(bytes[8] == math.maxInt(u8));
        try testing.expect(bytes[9] == math.maxInt(u8));
        try testing.expect(bytes[10] == math.maxInt(u8));
        try testing.expect(bytes[11] == math.maxInt(u8));
    }

    test "sliceAsBytes preserves pointer attributes" {
        const inArr align(16) = [2]u16{ 0xDEAD, 0xBEEF };
        const inSlice = @as(*align(16) const volatile [2]u16, @ptrCast(&inArr))[0..];
        const outSlice = sliceAsBytes(inSlice);

        const in = @typeInfo(@TypeOf(inSlice)).Pointer;
        const out = @typeInfo(@TypeOf(outSlice)).Pointer;

        try testing.expectEqual(in.is_const, out.is_const);
        try testing.expectEqual(in.is_volatile, out.is_volatile);
        try testing.expectEqual(in.is_allowzero, out.is_allowzero);
        try testing.expectEqual(in.alignment, out.alignment);
    }

    /// Round an address up to the next (or current) aligned address.
    /// The alignment must be a power of 2 and greater than 0.
    /// Asserts that rounding up the address does not cause integer overflow.
    pub fn alignForward(comptime T: type, addr: T, alignment: T) T {
        assert(isValidAlignGeneric(T, alignment));
        return alignBackward(T, addr + (alignment - 1), alignment);
    }

    pub fn alignForwardLog2(addr: usize, log2_alignment: u8) usize {
        const alignment = @as(usize, 1) << @as(math.Log2Int(usize), @intCast(log2_alignment));
        return alignForward(usize, addr, alignment);
    }

    pub const alignForwardGeneric = @compileError("renamed to alignForward");

    /// Force an evaluation of the expression; this tries to prevent
    /// the compiler from optimizing the computation away even if the
    /// result eventually gets discarded.
    // TODO: use @declareSideEffect() when it is available - https://github.com/ziglang/zig/issues/6168

    pub fn doNotOptimizeAway(val: anytype) void {
        var a: u8 = 0;
        if (@typeInfo(@TypeOf(.{a})).Struct.fields[0].is_comptime) return;

        const max_gp_register_bits = @bitSizeOf(c_long);
        const t = @typeInfo(@TypeOf(val));
        switch (t) {
            .Void, .Null, .ComptimeInt, .ComptimeFloat => return,
            .Enum => doNotOptimizeAway(@intFromEnum(val)),
            .Bool => doNotOptimizeAway(@intFromBool(val)),
            .Int => {
                const bits = t.Int.bits;
                if (bits <= max_gp_register_bits and builtin.zig_backend != .stage2_c) {
                    const val2 = @as(
                        std.meta.Int(t.Int.signedness, @max(8, std.math.ceilPowerOfTwoAssert(u16, bits))),
                        val,
                    );
                    asm volatile (""
                        :
                        : [val2] "r" (val2),
                    );
                } else doNotOptimizeAway(&val);
            },
            .Float => {
                if ((t.Float.bits == 32 or t.Float.bits == 64) and builtin.zig_backend != .stage2_c) {
                    asm volatile (""
                        :
                        : [val] "rm" (val),
                    );
                } else doNotOptimizeAway(&val);
            },
            .Pointer => {
                if (builtin.zig_backend == .stage2_c) {
                    doNotOptimizeAwayC(val);
                } else {
                    asm volatile (""
                        :
                        : [val] "m" (val),
                        : "memory"
                    );
                }
            },
            .Array => {
                if (t.Array.len * @sizeOf(t.Array.child) <= 64) {
                    for (val) |v| doNotOptimizeAway(v);
                } else doNotOptimizeAway(&val);
            },
            else => doNotOptimizeAway(&val),
        }
    }

    /// .stage2_c doesn't support asm blocks yet, so use volatile stores instead
    var deopt_target: if (builtin.zig_backend == .stage2_c) u8 else void = undefined;
    fn doNotOptimizeAwayC(ptr: anytype) void {
        const dest = @as(*volatile u8, @ptrCast(&deopt_target));
        for (asBytes(ptr)) |b| {
            dest.* = b;
        }
        dest.* = 0;
    }

    test "doNotOptimizeAway" {
        comptime doNotOptimizeAway("test");

        doNotOptimizeAway(null);
        doNotOptimizeAway(true);
        doNotOptimizeAway(0);
        doNotOptimizeAway(0.0);
        doNotOptimizeAway(@as(u1, 0));
        doNotOptimizeAway(@as(u3, 0));
        doNotOptimizeAway(@as(u8, 0));
        doNotOptimizeAway(@as(u16, 0));
        doNotOptimizeAway(@as(u32, 0));
        doNotOptimizeAway(@as(u64, 0));
        doNotOptimizeAway(@as(u128, 0));
        doNotOptimizeAway(@as(u13, 0));
        doNotOptimizeAway(@as(u37, 0));
        doNotOptimizeAway(@as(u96, 0));
        doNotOptimizeAway(@as(u200, 0));
        doNotOptimizeAway(@as(f32, 0.0));
        doNotOptimizeAway(@as(f64, 0.0));
        doNotOptimizeAway([_]u8{0} ** 4);
        doNotOptimizeAway([_]u8{0} ** 100);
        doNotOptimizeAway(@as(std.builtin.Endian, .Little));
    }

    test "alignForward" {
        try testing.expect(alignForward(usize, 1, 1) == 1);
        try testing.expect(alignForward(usize, 2, 1) == 2);
        try testing.expect(alignForward(usize, 1, 2) == 2);
        try testing.expect(alignForward(usize, 2, 2) == 2);
        try testing.expect(alignForward(usize, 3, 2) == 4);
        try testing.expect(alignForward(usize, 4, 2) == 4);
        try testing.expect(alignForward(usize, 7, 8) == 8);
        try testing.expect(alignForward(usize, 8, 8) == 8);
        try testing.expect(alignForward(usize, 9, 8) == 16);
        try testing.expect(alignForward(usize, 15, 8) == 16);
        try testing.expect(alignForward(usize, 16, 8) == 16);
        try testing.expect(alignForward(usize, 17, 8) == 24);
    }

    /// Round an address down to the previous (or current) aligned address.
    /// Unlike `alignBackward`, `alignment` can be any positive number, not just a power of 2.
    pub fn alignBackwardAnyAlign(i: usize, alignment: usize) usize {
        if (isValidAlign(alignment))
            return alignBackward(usize, i, alignment);
        assert(alignment != 0);
        return i - @mod(i, alignment);
    }

    /// Round an address down to the previous (or current) aligned address.
    /// The alignment must be a power of 2 and greater than 0.
    pub fn alignBackward(comptime T: type, addr: T, alignment: T) T {
        assert(isValidAlignGeneric(T, alignment));
        // 000010000 // example alignment

        // 000001111 // subtract 1

        // 111110000 // binary not

        return addr & ~(alignment - 1);
    }

    pub const alignBackwardGeneric = @compileError("renamed to alignBackward");

    /// Returns whether `alignment` is a valid alignment, meaning it is
    /// a positive power of 2.
    pub fn isValidAlign(alignment: usize) bool {
        return isValidAlignGeneric(usize, alignment);
    }

    /// Returns whether `alignment` is a valid alignment, meaning it is
    /// a positive power of 2.
    pub fn isValidAlignGeneric(comptime T: type, alignment: T) bool {
        return alignment > 0 and std.math.isPowerOfTwo(alignment);
    }

    pub fn isAlignedAnyAlign(i: usize, alignment: usize) bool {
        if (isValidAlign(alignment))
            return isAligned(i, alignment);
        assert(alignment != 0);
        return 0 == @mod(i, alignment);
    }

    pub fn isAlignedLog2(addr: usize, log2_alignment: u8) bool {
        return @ctz(addr) >= log2_alignment;
    }

    /// Given an address and an alignment, return true if the address is a multiple of the alignment
    /// The alignment must be a power of 2 and greater than 0.
    pub fn isAligned(addr: usize, alignment: usize) bool {
        return isAlignedGeneric(u64, addr, alignment);
    }

    pub fn isAlignedGeneric(comptime T: type, addr: T, alignment: T) bool {
        return alignBackward(T, addr, alignment) == addr;
    }

    test "isAligned" {
        try testing.expect(isAligned(0, 4));
        try testing.expect(isAligned(1, 1));
        try testing.expect(isAligned(2, 1));
        try testing.expect(isAligned(2, 2));
        try testing.expect(!isAligned(2, 4));
        try testing.expect(isAligned(3, 1));
        try testing.expect(!isAligned(3, 2));
        try testing.expect(!isAligned(3, 4));
        try testing.expect(isAligned(4, 4));
        try testing.expect(isAligned(4, 2));
        try testing.expect(isAligned(4, 1));
        try testing.expect(!isAligned(4, 8));
        try testing.expect(!isAligned(4, 16));
    }

    test "freeing empty string with null-terminated sentinel" {
        const empty_string = try testing.allocator.dupeZ(u8, "");
        testing.allocator.free(empty_string);
    }

    /// Returns a slice with the given new alignment,
    /// all other pointer attributes copied from `AttributeSource`.
    fn AlignedSlice(comptime AttributeSource: type, comptime new_alignment: usize) type {
        const info = @typeInfo(AttributeSource).Pointer;
        return @Type(.{
            .Pointer = .{
                .size = .Slice,
                .is_const = info.is_const,
                .is_volatile = info.is_volatile,
                .is_allowzero = info.is_allowzero,
                .alignment = new_alignment,
                .address_space = info.address_space,
                .child = info.child,
                .sentinel = null,
            },
        });
    }

    /// Returns the largest slice in the given bytes that conforms to the new alignment,
    /// or `null` if the given bytes contain no conforming address.
    pub fn alignInBytes(bytes: []u8, comptime new_alignment: usize) ?[]align(new_alignment) u8 {
        const begin_address = @intFromPtr(bytes.ptr);
        const end_address = begin_address + bytes.len;

        const begin_address_aligned = mem.alignForward(usize, begin_address, new_alignment);
        const new_length = std.math.sub(usize, end_address, begin_address_aligned) catch |e| switch (e) {
            error.Overflow => return null,
        };
        const alignment_offset = begin_address_aligned - begin_address;
        return @alignCast(bytes[alignment_offset .. alignment_offset + new_length]);
    }

    /// Returns the largest sub-slice within the given slice that conforms to the new alignment,
    /// or `null` if the given slice contains no conforming address.
    pub fn alignInSlice(slice: anytype, comptime new_alignment: usize) ?AlignedSlice(@TypeOf(slice), new_alignment) {
        const bytes = sliceAsBytes(slice);
        const aligned_bytes = alignInBytes(bytes, new_alignment) orelse return null;

        const Element = @TypeOf(slice[0]);
        const slice_length_bytes = aligned_bytes.len - (aligned_bytes.len % @sizeOf(Element));
        const aligned_slice = bytesAsSlice(Element, aligned_bytes[0..slice_length_bytes]);
        return @alignCast(aligned_slice);
    }

    test "read/write(Var)PackedInt" {
        if (builtin.zig_backend == .stage2_c) return error.SkipZigTest;

        switch (builtin.cpu.arch) {
            // This test generates too much code to execute on WASI.

            // LLVM backend fails with "too many locals: locals exceed maximum"

            .wasm32, .wasm64 => return error.SkipZigTest,
            else => {},
        }

        const foreign_endian: Endian = if (native_endian == .Big) .Little else .Big;
        const expect = std.testing.expect;
        var prng = std.rand.DefaultPrng.init(1234);
        const random = prng.random();

        @setEvalBranchQuota(10_000);
        inline for ([_]type{ u8, u16, u32, u128 }) |BackingType| {
            for ([_]BackingType{
                @as(BackingType, 0), // all zeros

                -%@as(BackingType, 1), // all ones

                random.int(BackingType), // random

                random.int(BackingType), // random

                random.int(BackingType), // random

            }) |init_value| {
                const uTs = [_]type{ u1, u3, u7, u8, u9, u10, u15, u16, u86 };
                const iTs = [_]type{ i1, i3, i7, i8, i9, i10, i15, i16, i86 };
                inline for (uTs ++ iTs) |PackedType| {
                    if (@bitSizeOf(PackedType) > @bitSizeOf(BackingType))
                        continue;

                    const iPackedType = std.meta.Int(.signed, @bitSizeOf(PackedType));
                    const uPackedType = std.meta.Int(.unsigned, @bitSizeOf(PackedType));
                    const Log2T = std.math.Log2Int(BackingType);

                    const offset_at_end = @bitSizeOf(BackingType) - @bitSizeOf(PackedType);
                    for ([_]usize{ 0, 1, 7, 8, 9, 10, 15, 16, 86, offset_at_end }) |offset| {
                        if (offset > offset_at_end or offset == @bitSizeOf(BackingType))
                            continue;

                        for ([_]PackedType{
                            ~@as(PackedType, 0), // all ones: -1 iN / maxInt uN

                            @as(PackedType, 0), // all zeros: 0 iN / 0 uN

                            @as(PackedType, @bitCast(@as(iPackedType, math.maxInt(iPackedType)))), // maxInt iN

                            @as(PackedType, @bitCast(@as(iPackedType, math.minInt(iPackedType)))), // maxInt iN

                            random.int(PackedType), // random

                            random.int(PackedType), // random

                        }) |write_value| {
                            { // Fixed-size Read/Write (Native-endian)

                                // Initialize Value

                                var value: BackingType = init_value;

                                // Read

                                const read_value1 = readPackedInt(PackedType, asBytes(&value), offset, native_endian);
                                try expect(read_value1 == @as(PackedType, @bitCast(@as(uPackedType, @truncate(value >> @as(Log2T, @intCast(offset)))))));

                                // Write

                                writePackedInt(PackedType, asBytes(&value), offset, write_value, native_endian);
                                try expect(write_value == @as(PackedType, @bitCast(@as(uPackedType, @truncate(value >> @as(Log2T, @intCast(offset)))))));

                                // Read again

                                const read_value2 = readPackedInt(PackedType, asBytes(&value), offset, native_endian);
                                try expect(read_value2 == write_value);

                                // Verify bits outside of the target integer are unmodified

                                const diff_bits = init_value ^ value;
                                if (offset != offset_at_end)
                                    try expect(diff_bits >> @as(Log2T, @intCast(offset + @bitSizeOf(PackedType))) == 0);
                                if (offset != 0)
                                    try expect(diff_bits << @as(Log2T, @intCast(@bitSizeOf(BackingType) - offset)) == 0);
                            }

                            { // Fixed-size Read/Write (Foreign-endian)

                                // Initialize Value

                                var value: BackingType = @byteSwap(init_value);

                                // Read

                                const read_value1 = readPackedInt(PackedType, asBytes(&value), offset, foreign_endian);
                                try expect(read_value1 == @as(PackedType, @bitCast(@as(uPackedType, @truncate(@byteSwap(value) >> @as(Log2T, @intCast(offset)))))));

                                // Write

                                writePackedInt(PackedType, asBytes(&value), offset, write_value, foreign_endian);
                                try expect(write_value == @as(PackedType, @bitCast(@as(uPackedType, @truncate(@byteSwap(value) >> @as(Log2T, @intCast(offset)))))));

                                // Read again

                                const read_value2 = readPackedInt(PackedType, asBytes(&value), offset, foreign_endian);
                                try expect(read_value2 == write_value);

                                // Verify bits outside of the target integer are unmodified

                                const diff_bits = init_value ^ @byteSwap(value);
                                if (offset != offset_at_end)
                                    try expect(diff_bits >> @as(Log2T, @intCast(offset + @bitSizeOf(PackedType))) == 0);
                                if (offset != 0)
                                    try expect(diff_bits << @as(Log2T, @intCast(@bitSizeOf(BackingType) - offset)) == 0);
                            }

                            const signedness = @typeInfo(PackedType).Int.signedness;
                            const NextPowerOfTwoInt = std.meta.Int(signedness, try comptime std.math.ceilPowerOfTwo(u16, @bitSizeOf(PackedType)));
                            const ui64 = std.meta.Int(signedness, 64);
                            inline for ([_]type{ PackedType, NextPowerOfTwoInt, ui64 }) |U| {
                                { // Variable-size Read/Write (Native-endian)

                                    if (@bitSizeOf(U) < @bitSizeOf(PackedType))
                                        continue;

                                    // Initialize Value

                                    var value: BackingType = init_value;

                                    // Read

                                    const read_value1 = readVarPackedInt(U, asBytes(&value), offset, @bitSizeOf(PackedType), native_endian, signedness);
                                    try expect(read_value1 == @as(PackedType, @bitCast(@as(uPackedType, @truncate(value >> @as(Log2T, @intCast(offset)))))));

                                    // Write

                                    writeVarPackedInt(asBytes(&value), offset, @bitSizeOf(PackedType), @as(U, write_value), native_endian);
                                    try expect(write_value == @as(PackedType, @bitCast(@as(uPackedType, @truncate(value >> @as(Log2T, @intCast(offset)))))));

                                    // Read again

                                    const read_value2 = readVarPackedInt(U, asBytes(&value), offset, @bitSizeOf(PackedType), native_endian, signedness);
                                    try expect(read_value2 == write_value);

                                    // Verify bits outside of the target integer are unmodified

                                    const diff_bits = init_value ^ value;
                                    if (offset != offset_at_end)
                                        try expect(diff_bits >> @as(Log2T, @intCast(offset + @bitSizeOf(PackedType))) == 0);
                                    if (offset != 0)
                                        try expect(diff_bits << @as(Log2T, @intCast(@bitSizeOf(BackingType) - offset)) == 0);
                                }

                                { // Variable-size Read/Write (Foreign-endian)

                                    if (@bitSizeOf(U) < @bitSizeOf(PackedType))
                                        continue;

                                    // Initialize Value

                                    var value: BackingType = @byteSwap(init_value);

                                    // Read

                                    const read_value1 = readVarPackedInt(U, asBytes(&value), offset, @bitSizeOf(PackedType), foreign_endian, signedness);
                                    try expect(read_value1 == @as(PackedType, @bitCast(@as(uPackedType, @truncate(@byteSwap(value) >> @as(Log2T, @intCast(offset)))))));

                                    // Write

                                    writeVarPackedInt(asBytes(&value), offset, @bitSizeOf(PackedType), @as(U, write_value), foreign_endian);
                                    try expect(write_value == @as(PackedType, @bitCast(@as(uPackedType, @truncate(@byteSwap(value) >> @as(Log2T, @intCast(offset)))))));

                                    // Read again

                                    const read_value2 = readVarPackedInt(U, asBytes(&value), offset, @bitSizeOf(PackedType), foreign_endian, signedness);
                                    try expect(read_value2 == write_value);

                                    // Verify bits outside of the target integer are unmodified

                                    const diff_bits = init_value ^ @byteSwap(value);
                                    if (offset != offset_at_end)
                                        try expect(diff_bits >> @as(Log2T, @intCast(offset + @bitSizeOf(PackedType))) == 0);
                                    if (offset != 0)
                                        try expect(diff_bits << @as(Log2T, @intCast(@bitSizeOf(BackingType) - offset)) == 0);
                                }
                            }
                        }
                    }
                }
            }
        }
    }