1 files changed, 177 insertions, 0 deletions
diff --git a/lib/std/math/complex/cosh.zig b/lib/std/math/complex/cosh.zig
new file mode 100644
index 0000000000..89afcac42e
--- /dev/null
+++ b/lib/std/math/complex/cosh.zig
@@ -0,0 +1,177 @@
+// 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/ccoshf.c
+// https://git.musl-libc.org/cgit/musl/tree/src/complex/ccosh.c
+
+const builtin = @import("builtin");
+const std = @import("../../std.zig");
+const testing = std.testing;
+const math = std.math;
+const cmath = math.complex;
+const Complex = cmath.Complex;
+
+const ldexp_cexp = @import("ldexp.zig").ldexp_cexp;
+
+/// Returns the hyperbolic arc-cosine of z.
+pub fn cosh(z: var) Complex(@typeOf(z.re)) {
+    const T = @typeOf(z.re);
+    return switch (T) {
+        f32 => cosh32(z),
+        f64 => cosh64(z),
+        else => @compileError("cosh not implemented for " ++ @typeName(z)),
+    };
+}
+
+fn cosh32(z: Complex(f32)) Complex(f32) {
+    const x = z.re;
+    const y = z.im;
+
+    const hx = @bitCast(u32, x);
+    const ix = hx & 0x7fffffff;
+
+    const hy = @bitCast(u32, y);
+    const iy = hy & 0x7fffffff;
+
+    if (ix < 0x7f800000 and iy < 0x7f800000) {
+        if (iy == 0) {
+            return Complex(f32).new(math.cosh(x), y);
+        }
+        // small x: normal case
+        if (ix < 0x41100000) {
+            return Complex(f32).new(math.cosh(x) * math.cos(y), math.sinh(x) * math.sin(y));
+        }
+
+        // |x|>= 9, so cosh(x) ~= exp(|x|)
+        if (ix < 0x42b17218) {
+            // x < 88.7: exp(|x|) won't overflow
+            const h = math.exp(math.fabs(x)) * 0.5;
+            return Complex(f32).new(math.copysign(f32, h, x) * math.cos(y), h * math.sin(y));
+        }
+        // x < 192.7: scale to avoid overflow
+        else if (ix < 0x4340b1e7) {
+            const v = Complex(f32).new(math.fabs(x), y);
+            const r = ldexp_cexp(v, -1);
+            return Complex(f32).new(r.re, r.im * math.copysign(f32, 1, x));
+        }
+        // x >= 192.7: result always overflows
+        else {
+            const h = 0x1p127 * x;
+            return Complex(f32).new(h * h * math.cos(y), h * math.sin(y));
+        }
+    }
+
+    if (ix == 0 and iy >= 0x7f800000) {
+        return Complex(f32).new(y - y, math.copysign(f32, 0, x * (y - y)));
+    }
+
+    if (iy == 0 and ix >= 0x7f800000) {
+        if (hx & 0x7fffff == 0) {
+            return Complex(f32).new(x * x, math.copysign(f32, 0, x) * y);
+        }
+        return Complex(f32).new(x, math.copysign(f32, 0, (x + x) * y));
+    }
+
+    if (ix < 0x7f800000 and iy >= 0x7f800000) {
+        return Complex(f32).new(y - y, x * (y - y));
+    }
+
+    if (ix >= 0x7f800000 and (hx & 0x7fffff) == 0) {
+        if (iy >= 0x7f800000) {
+            return Complex(f32).new(x * x, x * (y - y));
+        }
+        return Complex(f32).new((x * x) * math.cos(y), x * math.sin(y));
+    }
+
+    return Complex(f32).new((x * x) * (y - y), (x + x) * (y - y));
+}
+
+fn cosh64(z: Complex(f64)) Complex(f64) {
+    const x = z.re;
+    const y = z.im;
+
+    const fx = @bitCast(u64, x);
+    const hx = @intCast(u32, fx >> 32);
+    const lx = @truncate(u32, fx);
+    const ix = hx & 0x7fffffff;
+
+    const fy = @bitCast(u64, y);
+    const hy = @intCast(u32, fy >> 32);
+    const ly = @truncate(u32, fy);
+    const iy = hy & 0x7fffffff;
+
+    // nearly non-exceptional case where x, y are finite
+    if (ix < 0x7ff00000 and iy < 0x7ff00000) {
+        if (iy | ly == 0) {
+            return Complex(f64).new(math.cosh(x), x * y);
+        }
+        // small x: normal case
+        if (ix < 0x40360000) {
+            return Complex(f64).new(math.cosh(x) * math.cos(y), math.sinh(x) * math.sin(y));
+        }
+
+        // |x|>= 22, so cosh(x) ~= exp(|x|)
+        if (ix < 0x40862e42) {
+            // x < 710: exp(|x|) won't overflow
+            const h = math.exp(math.fabs(x)) * 0.5;
+            return Complex(f64).new(h * math.cos(y), math.copysign(f64, h, x) * math.sin(y));
+        }
+        // x < 1455: scale to avoid overflow
+        else if (ix < 0x4096bbaa) {
+            const v = Complex(f64).new(math.fabs(x), y);
+            const r = ldexp_cexp(v, -1);
+            return Complex(f64).new(r.re, r.im * math.copysign(f64, 1, x));
+        }
+        // x >= 1455: result always overflows
+        else {
+            const h = 0x1p1023;
+            return Complex(f64).new(h * h * math.cos(y), h * math.sin(y));
+        }
+    }
+
+    if (ix | lx == 0 and iy >= 0x7ff00000) {
+        return Complex(f64).new(y - y, math.copysign(f64, 0, x * (y - y)));
+    }
+
+    if (iy | ly == 0 and ix >= 0x7ff00000) {
+        if ((hx & 0xfffff) | lx == 0) {
+            return Complex(f64).new(x * x, math.copysign(f64, 0, x) * y);
+        }
+        return Complex(f64).new(x * x, math.copysign(f64, 0, (x + x) * y));
+    }
+
+    if (ix < 0x7ff00000 and iy >= 0x7ff00000) {
+        return Complex(f64).new(y - y, x * (y - y));
+    }
+
+    if (ix >= 0x7ff00000 and (hx & 0xfffff) | lx == 0) {
+        if (iy >= 0x7ff00000) {
+            return Complex(f64).new(x * x, x * (y - y));
+        }
+        return Complex(f64).new(x * x * math.cos(y), x * math.sin(y));
+    }
+
+    return Complex(f64).new((x * x) * (y - y), (x + x) * (y - y));
+}
+
+const epsilon = 0.0001;
+
+test "complex.ccosh32" {
+    const a = Complex(f32).new(5, 3);
+    const c = cosh(a);
+
+    testing.expect(math.approxEq(f32, c.re, -73.467300, epsilon));
+    testing.expect(math.approxEq(f32, c.im, 10.471557, epsilon));
+}
+
+test "complex.ccosh64" {
+    if (builtin.os == .linux and builtin.arch == .arm and builtin.abi == .musleabihf) {
+        // TODO https://github.com/ziglang/zig/issues/3289
+        return error.SkipZigTest;
+    }
+    const a = Complex(f64).new(5, 3);
+    const c = cosh(a);
+
+    testing.expect(math.approxEq(f64, c.re, -73.467300, epsilon));
+    testing.expect(math.approxEq(f64, c.im, 10.471557, epsilon));
+}