    // 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/complex/ctanhf.c

    // https://git.musl-libc.org/cgit/musl/tree/src/complex/ctanh.c

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

    /// Returns the hyperbolic tangent of z.
    pub fn tanh(z: anytype) @TypeOf(z) {
        const T = @TypeOf(z.re);
        return switch (T) {
            f32 => tanh32(z),
            f64 => tanh64(z),
            else => @compileError("tan not implemented for " ++ @typeName(z)),
        };
    }

    fn tanh32(z: Complex(f32)) Complex(f32) {
        const x = z.re;
        const y = z.im;

        const hx = @bitCast(u32, x);
        const ix = hx & 0x7fffffff;

        if (ix >= 0x7f800000) {
            if (ix & 0x7fffff != 0) {
                const r = if (y == 0) y else x * y;
                return Complex(f32).init(x, r);
            }
            const xx = @bitCast(f32, hx - 0x40000000);
            const r = if (math.isInf(y)) y else @sin(y) * @cos(y);
            return Complex(f32).init(xx, math.copysign(@as(f32, 0.0), r));
        }

        if (!math.isFinite(y)) {
            const r = if (ix != 0) y - y else x;
            return Complex(f32).init(r, y - y);
        }

        // x >= 11

        if (ix >= 0x41300000) {
            const exp_mx = @exp(-@fabs(x));
            return Complex(f32).init(math.copysign(@as(f32, 1.0), x), 4 * @sin(y) * @cos(y) * exp_mx * exp_mx);
        }

        // Kahan's algorithm

        const t = @tan(y);
        const beta = 1.0 + t * t;
        const s = math.sinh(x);
        const rho = @sqrt(1 + s * s);
        const den = 1 + beta * s * s;

        return Complex(f32).init((beta * rho * s) / den, t / den);
    }

    fn tanh64(z: Complex(f64)) Complex(f64) {
        const x = z.re;
        const y = z.im;

        const fx = @bitCast(u64, x);
        // TODO: zig should allow this conversion implicitly because it can notice that the value necessarily

        // fits in range.

        const hx = @intCast(u32, fx >> 32);
        const lx = @truncate(u32, fx);
        const ix = hx & 0x7fffffff;

        if (ix >= 0x7ff00000) {
            if ((ix & 0x7fffff) | lx != 0) {
                const r = if (y == 0) y else x * y;
                return Complex(f64).init(x, r);
            }

            const xx = @bitCast(f64, (@as(u64, hx - 0x40000000) << 32) | lx);
            const r = if (math.isInf(y)) y else @sin(y) * @cos(y);
            return Complex(f64).init(xx, math.copysign(@as(f64, 0.0), r));
        }

        if (!math.isFinite(y)) {
            const r = if (ix != 0) y - y else x;
            return Complex(f64).init(r, y - y);
        }

        // x >= 22

        if (ix >= 0x40360000) {
            const exp_mx = @exp(-@fabs(x));
            return Complex(f64).init(math.copysign(@as(f64, 1.0), x), 4 * @sin(y) * @cos(y) * exp_mx * exp_mx);
        }

        // Kahan's algorithm

        const t = @tan(y);
        const beta = 1.0 + t * t;
        const s = math.sinh(x);
        const rho = @sqrt(1 + s * s);
        const den = 1 + beta * s * s;

        return Complex(f64).init((beta * rho * s) / den, t / den);
    }

    const epsilon = 0.0001;

    test "complex.ctanh32" {
        const a = Complex(f32).init(5, 3);
        const c = tanh(a);

        try testing.expect(math.approxEqAbs(f32, c.re, 0.999913, epsilon));
        try testing.expect(math.approxEqAbs(f32, c.im, -0.000025, epsilon));
    }

    test "complex.ctanh64" {
        const a = Complex(f64).init(5, 3);
        const c = tanh(a);

        try testing.expect(math.approxEqAbs(f64, c.re, 0.999913, epsilon));
        try testing.expect(math.approxEqAbs(f64, c.im, -0.000025, epsilon));
    }