tanh.md

Levien tanh approximation

• license: Public Domain
• by Raph Levien and adpated by William Light

C:

inline static float
tanh_levien(const float x)
{
    const float x2 = x * x;
    const float x3 = x2 * x;
    const float x5 = x3 * x2;

    const float a = x
        + (0.16489087f * x3)
        + (0.00985468f * x5);

    return a / sqrtf(1.f + (a * a));
}

Rust:

#[inline]
pub fn tanh_levien(x: f32) -> f32 {
    let x2 = x * x;
    let x3 = x2 * x;
    let x5 = x3 * x2;
    
    let a = x
        + (0.16489087 * x3)
        + (0.00985468 * x5);
    
    a / (1.0 + (a * a)).sqrt()
}