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d29871977f
We already have a LICENSE file that covers the Zig Standard Library. We no longer need to remind everyone that the license is MIT in every single file. Previously this was introduced to clarify the situation for a fork of Zig that made Zig's LICENSE file harder to find, and replaced it with their own license that required annual payments to their company. However that fork now appears to be dead. So there is no need to reinforce the copyright notice in every single file.
123 lines
3.7 KiB
Zig
123 lines
3.7 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/sin.go
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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 cosine of the radian value x.
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///
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/// Special Cases:
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/// - cos(+-inf) = nan
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/// - cos(nan) = nan
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pub fn cos(x: anytype) @TypeOf(x) {
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const T = @TypeOf(x);
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return switch (T) {
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f32 => cos_(f32, x),
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f64 => cos_(f64, x),
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else => @compileError("cos not implemented for " ++ @typeName(T)),
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};
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}
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// sin polynomial coefficients
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const S0 = 1.58962301576546568060E-10;
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const S1 = -2.50507477628578072866E-8;
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const S2 = 2.75573136213857245213E-6;
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const S3 = -1.98412698295895385996E-4;
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const S4 = 8.33333333332211858878E-3;
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const S5 = -1.66666666666666307295E-1;
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// cos polynomial coeffiecients
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const C0 = -1.13585365213876817300E-11;
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const C1 = 2.08757008419747316778E-9;
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const C2 = -2.75573141792967388112E-7;
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const C3 = 2.48015872888517045348E-5;
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const C4 = -1.38888888888730564116E-3;
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const C5 = 4.16666666666665929218E-2;
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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 cos_(comptime T: type, x_: T) T {
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const I = std.meta.Int(.signed, @typeInfo(T).Float.bits);
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var x = x_;
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if (math.isNan(x) or math.isInf(x)) {
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return math.nan(T);
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}
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var sign = false;
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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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j &= 7;
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if (j > 3) {
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j -= 4;
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sign = !sign;
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}
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if (j > 1) {
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sign = !sign;
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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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const r = if (j == 1 or j == 2)
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z + z * w * (S5 + w * (S4 + w * (S3 + w * (S2 + w * (S1 + w * S0)))))
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else
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1.0 - 0.5 * w + w * w * (C5 + w * (C4 + w * (C3 + w * (C2 + w * (C1 + w * C0)))));
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return if (sign) -r else r;
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}
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test "math.cos" {
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try expect(cos(@as(f32, 0.0)) == cos_(f32, 0.0));
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try expect(cos(@as(f64, 0.0)) == cos_(f64, 0.0));
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}
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test "math.cos32" {
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const epsilon = 0.000001;
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try expect(math.approxEqAbs(f32, cos_(f32, 0.0), 1.0, epsilon));
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try expect(math.approxEqAbs(f32, cos_(f32, 0.2), 0.980067, epsilon));
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try expect(math.approxEqAbs(f32, cos_(f32, 0.8923), 0.627623, epsilon));
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try expect(math.approxEqAbs(f32, cos_(f32, 1.5), 0.070737, epsilon));
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try expect(math.approxEqAbs(f32, cos_(f32, -1.5), 0.070737, epsilon));
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try expect(math.approxEqAbs(f32, cos_(f32, 37.45), 0.969132, epsilon));
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try expect(math.approxEqAbs(f32, cos_(f32, 89.123), 0.400798, epsilon));
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}
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test "math.cos64" {
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const epsilon = 0.000001;
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try expect(math.approxEqAbs(f64, cos_(f64, 0.0), 1.0, epsilon));
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try expect(math.approxEqAbs(f64, cos_(f64, 0.2), 0.980067, epsilon));
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try expect(math.approxEqAbs(f64, cos_(f64, 0.8923), 0.627623, epsilon));
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try expect(math.approxEqAbs(f64, cos_(f64, 1.5), 0.070737, epsilon));
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try expect(math.approxEqAbs(f64, cos_(f64, -1.5), 0.070737, epsilon));
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try expect(math.approxEqAbs(f64, cos_(f64, 37.45), 0.969132, epsilon));
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try expect(math.approxEqAbs(f64, cos_(f64, 89.123), 0.40080, epsilon));
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}
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test "math.cos32.special" {
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try expect(math.isNan(cos_(f32, math.inf(f32))));
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try expect(math.isNan(cos_(f32, -math.inf(f32))));
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try expect(math.isNan(cos_(f32, math.nan(f32))));
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}
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test "math.cos64.special" {
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try expect(math.isNan(cos_(f64, math.inf(f64))));
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try expect(math.isNan(cos_(f64, -math.inf(f64))));
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try expect(math.isNan(cos_(f64, math.nan(f64))));
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}
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