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

    /// Returns the natural logarithm of x.
    ///
    /// Special Cases:
    ///  - ln(+inf)  = +inf
    ///  - ln(0)     = -inf
    ///  - ln(x)     = nan if x < 0
    ///  - ln(nan)   = nan
    ///  TODO remove this in favor of `@log`.
    pub fn ln(x: anytype) @TypeOf(x) {
        const T = @TypeOf(x);
        switch (@typeInfo(T)) {
            .ComptimeFloat => {
                return @as(comptime_float, @log(x));
            },
            .Float => return @log(x),
            .ComptimeInt => {
                return @as(comptime_int, @floor(@log(@as(f64, x))));
            },
            .Int => |IntType| switch (IntType.signedness) {
                .signed => @compileError("ln not implemented for signed integers"),
                .unsigned => return @as(T, @floor(@log(@as(f64, x)))),
            },
            else => @compileError("ln not implemented for " ++ @typeName(T)),
        }
    }

    test "math.ln" {
        try testing.expect(ln(@as(f32, 0.2)) == @log(0.2));
        try testing.expect(ln(@as(f64, 0.2)) == @log(0.2));
    }