1 files changed, 132 insertions, 0 deletions
diff --git a/lib/std/math/sinh.zig b/lib/std/math/sinh.zig
new file mode 100644
index 0000000000..73ee65ea6f
--- /dev/null
+++ b/lib/std/math/sinh.zig
@@ -0,0 +1,132 @@
+// 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/sinhf.c
+// https://git.musl-libc.org/cgit/musl/tree/src/math/sinh.c
+
+const builtin = @import("builtin");
+const std = @import("../std.zig");
+const math = std.math;
+const expect = std.testing.expect;
+const expo2 = @import("expo2.zig").expo2;
+const maxInt = std.math.maxInt;
+
+/// Returns the hyperbolic sine of x.
+///
+/// Special Cases:
+///  - sinh(+-0)   = +-0
+///  - sinh(+-inf) = +-inf
+///  - sinh(nan)   = nan
+pub fn sinh(x: var) @typeOf(x) {
+    const T = @typeOf(x);
+    return switch (T) {
+        f32 => sinh32(x),
+        f64 => sinh64(x),
+        else => @compileError("sinh not implemented for " ++ @typeName(T)),
+    };
+}
+
+// sinh(x) = (exp(x) - 1 / exp(x)) / 2
+//         = (exp(x) - 1 + (exp(x) - 1) / exp(x)) / 2
+//         = x + x^3 / 6 + o(x^5)
+fn sinh32(x: f32) f32 {
+    const u = @bitCast(u32, x);
+    const ux = u & 0x7FFFFFFF;
+    const ax = @bitCast(f32, ux);
+
+    if (x == 0.0 or math.isNan(x)) {
+        return x;
+    }
+
+    var h: f32 = 0.5;
+    if (u >> 31 != 0) {
+        h = -h;
+    }
+
+    // |x| < log(FLT_MAX)
+    if (ux < 0x42B17217) {
+        const t = math.expm1(ax);
+        if (ux < 0x3F800000) {
+            if (ux < 0x3F800000 - (12 << 23)) {
+                return x;
+            } else {
+                return h * (2 * t - t * t / (t + 1));
+            }
+        }
+        return h * (t + t / (t + 1));
+    }
+
+    // |x| > log(FLT_MAX) or nan
+    return 2 * h * expo2(ax);
+}
+
+fn sinh64(x: f64) f64 {
+    const u = @bitCast(u64, x);
+    const w = @intCast(u32, u >> 32);
+    const ax = @bitCast(f64, u & (maxInt(u64) >> 1));
+
+    if (x == 0.0 or math.isNan(x)) {
+        return x;
+    }
+
+    var h: f32 = 0.5;
+    if (u >> 63 != 0) {
+        h = -h;
+    }
+
+    // |x| < log(FLT_MAX)
+    if (w < 0x40862E42) {
+        const t = math.expm1(ax);
+        if (w < 0x3FF00000) {
+            if (w < 0x3FF00000 - (26 << 20)) {
+                return x;
+            } else {
+                return h * (2 * t - t * t / (t + 1));
+            }
+        }
+        // NOTE: |x| > log(0x1p26) + eps could be h * exp(x)
+        return h * (t + t / (t + 1));
+    }
+
+    // |x| > log(DBL_MAX) or nan
+    return 2 * h * expo2(ax);
+}
+
+test "math.sinh" {
+    expect(sinh(f32(1.5)) == sinh32(1.5));
+    expect(sinh(f64(1.5)) == sinh64(1.5));
+}
+
+test "math.sinh32" {
+    const epsilon = 0.000001;
+
+    expect(math.approxEq(f32, sinh32(0.0), 0.0, epsilon));
+    expect(math.approxEq(f32, sinh32(0.2), 0.201336, epsilon));
+    expect(math.approxEq(f32, sinh32(0.8923), 1.015512, epsilon));
+    expect(math.approxEq(f32, sinh32(1.5), 2.129279, epsilon));
+}
+
+test "math.sinh64" {
+    const epsilon = 0.000001;
+
+    expect(math.approxEq(f64, sinh64(0.0), 0.0, epsilon));
+    expect(math.approxEq(f64, sinh64(0.2), 0.201336, epsilon));
+    expect(math.approxEq(f64, sinh64(0.8923), 1.015512, epsilon));
+    expect(math.approxEq(f64, sinh64(1.5), 2.129279, epsilon));
+}
+
+test "math.sinh32.special" {
+    expect(sinh32(0.0) == 0.0);
+    expect(sinh32(-0.0) == -0.0);
+    expect(math.isPositiveInf(sinh32(math.inf(f32))));
+    expect(math.isNegativeInf(sinh32(-math.inf(f32))));
+    expect(math.isNan(sinh32(math.nan(f32))));
+}
+
+test "math.sinh64.special" {
+    expect(sinh64(0.0) == 0.0);
+    expect(sinh64(-0.0) == -0.0);
+    expect(math.isPositiveInf(sinh64(math.inf(f64))));
+    expect(math.isNegativeInf(sinh64(-math.inf(f64))));
+    expect(math.isNan(sinh64(math.nan(f64))));
+}