    const std = @import("../std.zig");
    const builtin = @import("builtin");
    const math = std.math;
    const expect = std.testing.expect;

    /// Returns the base-2 logarithm of x.
    ///
    /// Special Cases:
    ///  - log2(+inf)  = +inf
    ///  - log2(0)     = -inf
    ///  - log2(x)     = nan if x < 0
    ///  - log2(nan)   = nan
    pub fn log2(x: anytype) @TypeOf(x) {
        const T = @TypeOf(x);
        switch (@typeInfo(T)) {
            .ComptimeFloat => {
                return @as(comptime_float, @log2(x));
            },
            .Float => return @log2(x),
            .ComptimeInt => comptime {
                var x_shifted = x;
                // First, calculate floorPowerOfTwo(x)

                var shift_amt = 1;
                while (x_shifted >> (shift_amt << 1) != 0) shift_amt <<= 1;

                // Answer is in the range [shift_amt, 2 * shift_amt - 1]

                // We can find it in O(log(N)) using binary search.

                var result = 0;
                while (shift_amt != 0) : (shift_amt >>= 1) {
                    if (x_shifted >> shift_amt != 0) {
                        x_shifted >>= shift_amt;
                        result += shift_amt;
                    }
                }
                return result;
            },
            .Int => |IntType| switch (IntType.signedness) {
                .signed => @compileError("log2 not implemented for signed integers"),
                .unsigned => return math.log2_int(T, x),
            },
            else => @compileError("log2 not implemented for " ++ @typeName(T)),
        }
    }

    test "log2" {
        // https://github.com/ziglang/zig/issues/13703

        if (builtin.cpu.arch == .aarch64 and builtin.os.tag == .windows) return error.SkipZigTest;

        try expect(log2(@as(f32, 0.2)) == @log2(0.2));
        try expect(log2(@as(f64, 0.2)) == @log2(0.2));
        comptime {
            try expect(log2(1) == 0);
            try expect(log2(15) == 3);
            try expect(log2(16) == 4);
            try expect(log2(1 << 4073) == 4073);
        }
    }