98 lines
2.4 KiB
Zig
98 lines
2.4 KiB
Zig
// SPDX-License-Identifier: MIT
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// Copyright (c) 2015-2020 Zig Contributors
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// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
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// The MIT license requires this copyright notice to be included in all copies
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// and substantial portions of the software.
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// 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/scalbnf.c
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// https://git.musl-libc.org/cgit/musl/tree/src/math/scalbn.c
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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 x * 2^n.
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pub fn scalbn(x: anytype, n: i32) @TypeOf(x) {
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const T = @TypeOf(x);
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return switch (T) {
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f32 => scalbn32(x, n),
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f64 => scalbn64(x, n),
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else => @compileError("scalbn not implemented for " ++ @typeName(T)),
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};
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}
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fn scalbn32(x: f32, n_: i32) f32 {
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var y = x;
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var n = n_;
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if (n > 127) {
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y *= 0x1.0p127;
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n -= 127;
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if (n > 1023) {
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y *= 0x1.0p127;
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n -= 127;
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if (n > 127) {
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n = 127;
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}
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}
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} else if (n < -126) {
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y *= 0x1.0p-126 * 0x1.0p24;
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n += 126 - 24;
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if (n < -126) {
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y *= 0x1.0p-126 * 0x1.0p24;
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n += 126 - 24;
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if (n < -126) {
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n = -126;
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}
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}
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}
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const u = @intCast(u32, n +% 0x7F) << 23;
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return y * @bitCast(f32, u);
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}
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fn scalbn64(x: f64, n_: i32) f64 {
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var y = x;
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var n = n_;
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if (n > 1023) {
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y *= 0x1.0p1023;
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n -= 1023;
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if (n > 1023) {
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y *= 0x1.0p1023;
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n -= 1023;
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if (n > 1023) {
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n = 1023;
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}
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}
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} else if (n < -1022) {
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y *= 0x1.0p-1022 * 0x1.0p53;
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n += 1022 - 53;
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if (n < -1022) {
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y *= 0x1.0p-1022 * 0x1.0p53;
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n += 1022 - 53;
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if (n < -1022) {
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n = -1022;
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}
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}
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}
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const u = @intCast(u64, n +% 0x3FF) << 52;
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return y * @bitCast(f64, u);
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}
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test "math.scalbn" {
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expect(scalbn(@as(f32, 1.5), 4) == scalbn32(1.5, 4));
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expect(scalbn(@as(f64, 1.5), 4) == scalbn64(1.5, 4));
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}
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test "math.scalbn32" {
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expect(scalbn32(1.5, 4) == 24.0);
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}
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test "math.scalbn64" {
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expect(scalbn64(1.5, 4) == 24.0);
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}
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