    // Ported from musl, which is licensed under the MIT license:

    // https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT

    //

    // https://git.musl-libc.org/cgit/musl/tree/src/math/asinhf.c

    // https://git.musl-libc.org/cgit/musl/tree/src/math/asinh.c

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

    /// Returns the hyperbolic arc-sin of x.
    ///
    /// Special Cases:
    ///  - asinh(+-0)   = +-0
    ///  - asinh(+-inf) = +-inf
    ///  - asinh(nan)   = nan
    pub fn asinh(x: anytype) @TypeOf(x) {
        const T = @TypeOf(x);
        return switch (T) {
            f32 => asinh32(x),
            f64 => asinh64(x),
            else => @compileError("asinh not implemented for " ++ @typeName(T)),
        };
    }

    // asinh(x) = sign(x) * log(|x| + sqrt(x * x + 1)) ~= x - x^3/6 + o(x^5)

    fn asinh32(x: f32) f32 {
        const u = @as(u32, @bitCast(x));
        const i = u & 0x7FFFFFFF;
        const s = i >> 31;

        var rx = @as(f32, @bitCast(i)); // |x|

        // TODO: Shouldn't need this explicit check.

        if (math.isNegativeInf(x)) {
            return x;
        }

        // |x| >= 0x1p12 or inf or nan

        if (i >= 0x3F800000 + (12 << 23)) {
            rx = @log(rx) + 0.69314718055994530941723212145817656;
        }
        // |x| >= 2

        else if (i >= 0x3F800000 + (1 << 23)) {
            rx = @log(2 * x + 1 / (@sqrt(x * x + 1) + x));
        }
        // |x| >= 0x1p-12, up to 1.6ulp error

        else if (i >= 0x3F800000 - (12 << 23)) {
            rx = math.log1p(x + x * x / (@sqrt(x * x + 1) + 1));
        }
        // |x| < 0x1p-12, inexact if x != 0

        else {
            math.doNotOptimizeAway(x + 0x1.0p120);
        }

        return if (s != 0) -rx else rx;
    }

    fn asinh64(x: f64) f64 {
        const u = @as(u64, @bitCast(x));
        const e = (u >> 52) & 0x7FF;
        const s = e >> 63;

        var rx = @as(f64, @bitCast(u & (maxInt(u64) >> 1))); // |x|

        if (math.isNegativeInf(x)) {
            return x;
        }

        // |x| >= 0x1p26 or inf or nan

        if (e >= 0x3FF + 26) {
            rx = @log(rx) + 0.693147180559945309417232121458176568;
        }
        // |x| >= 2

        else if (e >= 0x3FF + 1) {
            rx = @log(2 * x + 1 / (@sqrt(x * x + 1) + x));
        }
        // |x| >= 0x1p-12, up to 1.6ulp error

        else if (e >= 0x3FF - 26) {
            rx = math.log1p(x + x * x / (@sqrt(x * x + 1) + 1));
        }
        // |x| < 0x1p-12, inexact if x != 0

        else {
            math.doNotOptimizeAway(x + 0x1.0p120);
        }

        return if (s != 0) -rx else rx;
    }

    test "math.asinh" {
        try expect(asinh(@as(f32, 0.0)) == asinh32(0.0));
        try expect(asinh(@as(f64, 0.0)) == asinh64(0.0));
    }

    test "math.asinh32" {
        const epsilon = 0.000001;

        try expect(math.approxEqAbs(f32, asinh32(0.0), 0.0, epsilon));
        try expect(math.approxEqAbs(f32, asinh32(-0.2), -0.198690, epsilon));
        try expect(math.approxEqAbs(f32, asinh32(0.2), 0.198690, epsilon));
        try expect(math.approxEqAbs(f32, asinh32(0.8923), 0.803133, epsilon));
        try expect(math.approxEqAbs(f32, asinh32(1.5), 1.194763, epsilon));
        try expect(math.approxEqAbs(f32, asinh32(37.45), 4.316332, epsilon));
        try expect(math.approxEqAbs(f32, asinh32(89.123), 5.183196, epsilon));
        try expect(math.approxEqAbs(f32, asinh32(123123.234375), 12.414088, epsilon));
    }

    test "math.asinh64" {
        const epsilon = 0.000001;

        try expect(math.approxEqAbs(f64, asinh64(0.0), 0.0, epsilon));
        try expect(math.approxEqAbs(f64, asinh64(-0.2), -0.198690, epsilon));
        try expect(math.approxEqAbs(f64, asinh64(0.2), 0.198690, epsilon));
        try expect(math.approxEqAbs(f64, asinh64(0.8923), 0.803133, epsilon));
        try expect(math.approxEqAbs(f64, asinh64(1.5), 1.194763, epsilon));
        try expect(math.approxEqAbs(f64, asinh64(37.45), 4.316332, epsilon));
        try expect(math.approxEqAbs(f64, asinh64(89.123), 5.183196, epsilon));
        try expect(math.approxEqAbs(f64, asinh64(123123.234375), 12.414088, epsilon));
    }

    test "math.asinh32.special" {
        try expect(asinh32(0.0) == 0.0);
        try expect(asinh32(-0.0) == -0.0);
        try expect(math.isPositiveInf(asinh32(math.inf(f32))));
        try expect(math.isNegativeInf(asinh32(-math.inf(f32))));
        try expect(math.isNan(asinh32(math.nan(f32))));
    }

    test "math.asinh64.special" {
        try expect(asinh64(0.0) == 0.0);
        try expect(asinh64(-0.0) == -0.0);
        try expect(math.isPositiveInf(asinh64(math.inf(f64))));
        try expect(math.isNegativeInf(asinh64(-math.inf(f64))));
        try expect(math.isNan(asinh64(math.nan(f64))));
    }