1// Ported from musl, which is licensed under the MIT license:
 2// https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
 3//
 4// https://git.musl-libc.org/cgit/musl/tree/src/math/__expo2f.c
 5// https://git.musl-libc.org/cgit/musl/tree/src/math/__expo2.c
 6
 7const math = @import("../math.zig");
 8
 9/// Returns exp(x) / 2 for x >= log(maxFloat(T)).
10pub fn expo2(x: anytype) @TypeOf(x) {
11    const T = @TypeOf(x);
12    return switch (T) {
13        f32 => expo2f(x),
14        f64 => expo2d(x),
15        else => @compileError("expo2 not implemented for " ++ @typeName(T)),
16    };
17}
18
19fn expo2f(x: f32) f32 {
20    const k: u32 = 235;
21    const kln2 = 0x1.45C778p+7;
22
23    const u = (0x7F + k / 2) << 23;
24    const scale = @as(f32, @bitCast(u));
25    return @exp(x - kln2) * scale * scale;
26}
27
28fn expo2d(x: f64) f64 {
29    const k: u32 = 2043;
30    const kln2 = 0x1.62066151ADD8BP+10;
31
32    const u = (0x3FF + k / 2) << 20;
33    const scale = @as(f64, @bitCast(@as(u64, u) << 32));
34    return @exp(x - kln2) * scale * scale;
35}