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}