1 files changed, 122 insertions, 0 deletions
diff --git a/lib/std/math/tan.zig b/lib/std/math/tan.zig
new file mode 100644
index 0000000000..049c85df12
--- /dev/null
+++ b/lib/std/math/tan.zig
@@ -0,0 +1,122 @@
+// Ported from go, which is licensed under a BSD-3 license.
+// https://golang.org/LICENSE
+//
+// https://golang.org/src/math/tan.go
+
+const builtin = @import("builtin");
+const std = @import("../std.zig");
+const math = std.math;
+const expect = std.testing.expect;
+
+/// Returns the tangent of the radian value x.
+///
+/// Special Cases:
+///  - tan(+-0)   = +-0
+///  - tan(+-inf) = nan
+///  - tan(nan)   = nan
+pub fn tan(x: var) @typeOf(x) {
+    const T = @typeOf(x);
+    return switch (T) {
+        f32 => tan_(f32, x),
+        f64 => tan_(f64, x),
+        else => @compileError("tan not implemented for " ++ @typeName(T)),
+    };
+}
+
+const Tp0 = -1.30936939181383777646E4;
+const Tp1 = 1.15351664838587416140E6;
+const Tp2 = -1.79565251976484877988E7;
+
+const Tq1 = 1.36812963470692954678E4;
+const Tq2 = -1.32089234440210967447E6;
+const Tq3 = 2.50083801823357915839E7;
+const Tq4 = -5.38695755929454629881E7;
+
+const pi4a = 7.85398125648498535156e-1;
+const pi4b = 3.77489470793079817668E-8;
+const pi4c = 2.69515142907905952645E-15;
+const m4pi = 1.273239544735162542821171882678754627704620361328125;
+
+fn tan_(comptime T: type, x_: T) T {
+    const I = @IntType(true, T.bit_count);
+
+    var x = x_;
+    if (x == 0 or math.isNan(x)) {
+        return x;
+    }
+    if (math.isInf(x)) {
+        return math.nan(T);
+    }
+
+    var sign = x < 0;
+    x = math.fabs(x);
+
+    var y = math.floor(x * m4pi);
+    var j = @floatToInt(I, y);
+
+    if (j & 1 == 1) {
+        j += 1;
+        y += 1;
+    }
+
+    const z = ((x - y * pi4a) - y * pi4b) - y * pi4c;
+    const w = z * z;
+
+    var r = if (w > 1e-14)
+        z + z * (w * ((Tp0 * w + Tp1) * w + Tp2) / ((((w + Tq1) * w + Tq2) * w + Tq3) * w + Tq4))
+    else
+        z;
+
+    if (j & 2 == 2) {
+        r = -1 / r;
+    }
+
+    return if (sign) -r else r;
+}
+
+test "math.tan" {
+    expect(tan(f32(0.0)) == tan_(f32, 0.0));
+    expect(tan(f64(0.0)) == tan_(f64, 0.0));
+}
+
+test "math.tan32" {
+    const epsilon = 0.000001;
+
+    expect(math.approxEq(f32, tan_(f32, 0.0), 0.0, epsilon));
+    expect(math.approxEq(f32, tan_(f32, 0.2), 0.202710, epsilon));
+    expect(math.approxEq(f32, tan_(f32, 0.8923), 1.240422, epsilon));
+    expect(math.approxEq(f32, tan_(f32, 1.5), 14.101420, epsilon));
+    expect(math.approxEq(f32, tan_(f32, 37.45), -0.254397, epsilon));
+    expect(math.approxEq(f32, tan_(f32, 89.123), 2.285852, epsilon));
+}
+
+test "math.tan64" {
+    if (builtin.os == .linux and builtin.arch == .arm and builtin.abi == .musleabihf) {
+        // TODO https://github.com/ziglang/zig/issues/3289
+        return error.SkipZigTest;
+    }
+    const epsilon = 0.000001;
+
+    expect(math.approxEq(f64, tan_(f64, 0.0), 0.0, epsilon));
+    expect(math.approxEq(f64, tan_(f64, 0.2), 0.202710, epsilon));
+    expect(math.approxEq(f64, tan_(f64, 0.8923), 1.240422, epsilon));
+    expect(math.approxEq(f64, tan_(f64, 1.5), 14.101420, epsilon));
+    expect(math.approxEq(f64, tan_(f64, 37.45), -0.254397, epsilon));
+    expect(math.approxEq(f64, tan_(f64, 89.123), 2.2858376, epsilon));
+}
+
+test "math.tan32.special" {
+    expect(tan_(f32, 0.0) == 0.0);
+    expect(tan_(f32, -0.0) == -0.0);
+    expect(math.isNan(tan_(f32, math.inf(f32))));
+    expect(math.isNan(tan_(f32, -math.inf(f32))));
+    expect(math.isNan(tan_(f32, math.nan(f32))));
+}
+
+test "math.tan64.special" {
+    expect(tan_(f64, 0.0) == 0.0);
+    expect(tan_(f64, -0.0) == -0.0);
+    expect(math.isNan(tan_(f64, math.inf(f64))));
+    expect(math.isNan(tan_(f64, -math.inf(f64))));
+    expect(math.isNan(tan_(f64, math.nan(f64))));
+}