zig/std/math/expo2.zig

const math = @import("index.zig");

pub fn expo2(x: var) -> @typeOf(x) {
    const T = @typeOf(x);
    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 = @bitCast(f32, u);
    math.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 = @bitCast(f64, u64(u) << 32);
    math.exp(x - kln2) * scale * scale
}