127 lines
2.9 KiB
Zig
127 lines
2.9 KiB
Zig
// Ported from musl, which is licensed under the MIT license:
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// https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
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//
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// https://git.musl-libc.org/cgit/musl/tree/src/math/roundf.c
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// https://git.musl-libc.org/cgit/musl/tree/src/math/round.c
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const builtin = @import("builtin");
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const expect = std.testing.expect;
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const std = @import("../std.zig");
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const math = std.math;
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/// Returns x rounded to the nearest integer, rounding half away from zero.
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///
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/// Special Cases:
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/// - round(+-0) = +-0
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/// - round(+-inf) = +-inf
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/// - round(nan) = nan
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pub fn round(x: var) @typeOf(x) {
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const T = @typeOf(x);
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return switch (T) {
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f32 => round32(x),
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f64 => round64(x),
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else => @compileError("round not implemented for " ++ @typeName(T)),
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};
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}
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fn round32(x_: f32) f32 {
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var x = x_;
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const u = @bitCast(u32, x);
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const e = (u >> 23) & 0xFF;
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var y: f32 = undefined;
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if (e >= 0x7F + 23) {
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return x;
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}
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if (u >> 31 != 0) {
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x = -x;
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}
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if (e < 0x7F - 1) {
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math.forceEval(x + math.f32_toint);
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return 0 * @bitCast(f32, u);
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}
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y = x + math.f32_toint - math.f32_toint - x;
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if (y > 0.5) {
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y = y + x - 1;
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} else if (y <= -0.5) {
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y = y + x + 1;
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} else {
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y = y + x;
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}
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if (u >> 31 != 0) {
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return -y;
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} else {
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return y;
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}
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}
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fn round64(x_: f64) f64 {
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var x = x_;
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const u = @bitCast(u64, x);
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const e = (u >> 52) & 0x7FF;
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var y: f64 = undefined;
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if (e >= 0x3FF + 52) {
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return x;
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}
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if (u >> 63 != 0) {
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x = -x;
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}
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if (e < 0x3ff - 1) {
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math.forceEval(x + math.f64_toint);
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return 0 * @bitCast(f64, u);
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}
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y = x + math.f64_toint - math.f64_toint - x;
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if (y > 0.5) {
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y = y + x - 1;
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} else if (y <= -0.5) {
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y = y + x + 1;
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} else {
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y = y + x;
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}
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if (u >> 63 != 0) {
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return -y;
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} else {
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return y;
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}
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}
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test "math.round" {
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expect(round(f32(1.3)) == round32(1.3));
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expect(round(f64(1.3)) == round64(1.3));
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}
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test "math.round32" {
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expect(round32(1.3) == 1.0);
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expect(round32(-1.3) == -1.0);
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expect(round32(0.2) == 0.0);
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expect(round32(1.8) == 2.0);
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}
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test "math.round64" {
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expect(round64(1.3) == 1.0);
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expect(round64(-1.3) == -1.0);
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expect(round64(0.2) == 0.0);
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expect(round64(1.8) == 2.0);
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}
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test "math.round32.special" {
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expect(round32(0.0) == 0.0);
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expect(round32(-0.0) == -0.0);
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expect(math.isPositiveInf(round32(math.inf(f32))));
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expect(math.isNegativeInf(round32(-math.inf(f32))));
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expect(math.isNan(round32(math.nan(f32))));
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}
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test "math.round64.special" {
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expect(round64(0.0) == 0.0);
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expect(round64(-0.0) == -0.0);
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expect(math.isPositiveInf(round64(math.inf(f64))));
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expect(math.isNegativeInf(round64(-math.inf(f64))));
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expect(math.isNan(round64(math.nan(f64))));
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}
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