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36// 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/__expo2f.c
// https://git.musl-libc.org/cgit/musl/tree/src/math/__expo2.c
const math = @import("../math.zig");
/// Returns exp(x) / 2 for x >= log(maxFloat(T)).
pub fn expo2(x: anytype) @TypeOf(x) {
const T = @TypeOf(x);
return switch (T) {
f32 => expo2f(x),
f64 => expo2d(x),
else => @compileError("expo2 not implemented for " ++ @typeName(T)),
};
}
fn expo2f(x: f32) f32 {
const k: u32 = 235;
const kln2 = 0x1.45C778p+7;
const u = (0x7F + k / 2) << 23;
const scale = @as(f32, @bitCast(u));
return @exp(x - kln2) * scale * scale;
}
fn expo2d(x: f64) f64 {
const k: u32 = 2043;
const kln2 = 0x1.62066151ADD8BP+10;
const u = (0x3FF + k / 2) << 20;
const scale = @as(f64, @bitCast(@as(u64, u) << 32));
return @exp(x - kln2) * scale * scale;
}