119 lines
3.3 KiB
Zig
119 lines
3.3 KiB
Zig
// Ported from go, which is licensed under a BSD-3 license.
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// https://golang.org/LICENSE
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//
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// https://golang.org/src/math/tan.go
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const builtin = @import("builtin");
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const std = @import("../std.zig");
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const math = std.math;
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const expect = std.testing.expect;
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/// Returns the tangent of the radian value x.
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///
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/// Special Cases:
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/// - tan(+-0) = +-0
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/// - tan(+-inf) = nan
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/// - tan(nan) = nan
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pub fn tan(x: var) @TypeOf(x) {
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const T = @TypeOf(x);
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return switch (T) {
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f32 => tan_(f32, x),
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f64 => tan_(f64, x),
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else => @compileError("tan not implemented for " ++ @typeName(T)),
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};
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}
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const Tp0 = -1.30936939181383777646E4;
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const Tp1 = 1.15351664838587416140E6;
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const Tp2 = -1.79565251976484877988E7;
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const Tq1 = 1.36812963470692954678E4;
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const Tq2 = -1.32089234440210967447E6;
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const Tq3 = 2.50083801823357915839E7;
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const Tq4 = -5.38695755929454629881E7;
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const pi4a = 7.85398125648498535156e-1;
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const pi4b = 3.77489470793079817668E-8;
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const pi4c = 2.69515142907905952645E-15;
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const m4pi = 1.273239544735162542821171882678754627704620361328125;
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fn tan_(comptime T: type, x_: T) T {
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const I = std.meta.IntType(true, T.bit_count);
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var x = x_;
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if (x == 0 or math.isNan(x)) {
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return x;
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}
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if (math.isInf(x)) {
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return math.nan(T);
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}
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var sign = x < 0;
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x = math.fabs(x);
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var y = math.floor(x * m4pi);
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var j = @floatToInt(I, y);
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if (j & 1 == 1) {
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j += 1;
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y += 1;
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}
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const z = ((x - y * pi4a) - y * pi4b) - y * pi4c;
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const w = z * z;
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var r = if (w > 1e-14)
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z + z * (w * ((Tp0 * w + Tp1) * w + Tp2) / ((((w + Tq1) * w + Tq2) * w + Tq3) * w + Tq4))
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else
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z;
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if (j & 2 == 2) {
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r = -1 / r;
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}
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return if (sign) -r else r;
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}
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test "math.tan" {
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expect(tan(@as(f32, 0.0)) == tan_(f32, 0.0));
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expect(tan(@as(f64, 0.0)) == tan_(f64, 0.0));
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}
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test "math.tan32" {
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const epsilon = 0.000001;
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expect(math.approxEq(f32, tan_(f32, 0.0), 0.0, epsilon));
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expect(math.approxEq(f32, tan_(f32, 0.2), 0.202710, epsilon));
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expect(math.approxEq(f32, tan_(f32, 0.8923), 1.240422, epsilon));
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expect(math.approxEq(f32, tan_(f32, 1.5), 14.101420, epsilon));
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expect(math.approxEq(f32, tan_(f32, 37.45), -0.254397, epsilon));
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expect(math.approxEq(f32, tan_(f32, 89.123), 2.285852, epsilon));
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}
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test "math.tan64" {
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const epsilon = 0.000001;
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expect(math.approxEq(f64, tan_(f64, 0.0), 0.0, epsilon));
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expect(math.approxEq(f64, tan_(f64, 0.2), 0.202710, epsilon));
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expect(math.approxEq(f64, tan_(f64, 0.8923), 1.240422, epsilon));
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expect(math.approxEq(f64, tan_(f64, 1.5), 14.101420, epsilon));
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expect(math.approxEq(f64, tan_(f64, 37.45), -0.254397, epsilon));
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expect(math.approxEq(f64, tan_(f64, 89.123), 2.2858376, epsilon));
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}
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test "math.tan32.special" {
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expect(tan_(f32, 0.0) == 0.0);
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expect(tan_(f32, -0.0) == -0.0);
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expect(math.isNan(tan_(f32, math.inf(f32))));
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expect(math.isNan(tan_(f32, -math.inf(f32))));
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expect(math.isNan(tan_(f32, math.nan(f32))));
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}
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test "math.tan64.special" {
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expect(tan_(f64, 0.0) == 0.0);
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expect(tan_(f64, -0.0) == -0.0);
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expect(math.isNan(tan_(f64, math.inf(f64))));
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expect(math.isNan(tan_(f64, -math.inf(f64))));
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expect(math.isNan(tan_(f64, math.nan(f64))));
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}
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