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// SPDX-License-Identifier: MIT
// Copyright (c) 2015-2021 Zig Contributors
// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
// The MIT license requires this copyright notice to be included in all copies
// and substantial portions of the software.
// Ported from musl, which is licensed under the MIT license:
// https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
//
// https://git.musl-libc.org/cgit/musl/tree/src/math/scalbnf.c
// https://git.musl-libc.org/cgit/musl/tree/src/math/scalbn.c
const std = @import("../std.zig");
const math = std.math;
const expect = std.testing.expect;
/// Returns x * 2^n.
pub fn scalbn(x: anytype, n: i32) @TypeOf(x) {
const T = @TypeOf(x);
return switch (T) {
f32 => scalbn32(x, n),
f64 => scalbn64(x, n),
else => @compileError("scalbn not implemented for " ++ @typeName(T)),
};
}
fn scalbn32(x: f32, n_: i32) f32 {
var y = x;
var n = n_;
if (n > 127) {
y *= 0x1.0p127;
n -= 127;
if (n > 1023) {
y *= 0x1.0p127;
n -= 127;
if (n > 127) {
n = 127;
}
}
} else if (n < -126) {
y *= 0x1.0p-126 * 0x1.0p24;
n += 126 - 24;
if (n < -126) {
y *= 0x1.0p-126 * 0x1.0p24;
n += 126 - 24;
if (n < -126) {
n = -126;
}
}
}
const u = @intCast(u32, n +% 0x7F) << 23;
return y * @bitCast(f32, u);
}
fn scalbn64(x: f64, n_: i32) f64 {
var y = x;
var n = n_;
if (n > 1023) {
y *= 0x1.0p1023;
n -= 1023;
if (n > 1023) {
y *= 0x1.0p1023;
n -= 1023;
if (n > 1023) {
n = 1023;
}
}
} else if (n < -1022) {
y *= 0x1.0p-1022 * 0x1.0p53;
n += 1022 - 53;
if (n < -1022) {
y *= 0x1.0p-1022 * 0x1.0p53;
n += 1022 - 53;
if (n < -1022) {
n = -1022;
}
}
}
const u = @intCast(u64, n +% 0x3FF) << 52;
return y * @bitCast(f64, u);
}
test "math.scalbn" {
expect(scalbn(@as(f32, 1.5), 4) == scalbn32(1.5, 4));
expect(scalbn(@as(f64, 1.5), 4) == scalbn64(1.5, 4));
}
test "math.scalbn32" {
expect(scalbn32(1.5, 4) == 24.0);
}
test "math.scalbn64" {
expect(scalbn64(1.5, 4) == 24.0);
}
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