#[inline]
pub fn inverse_sqrt(n: f32) -> f32 {
    1f32 / n.sqrt()
}

union MixedIntFloat {
    f: f32,
    i: u32,
}

/// see https://en.wikipedia.org/wiki/Fast_inverse_square_root
#[inline]
pub fn fast_inverse_sqrt(n: f32) -> f32 {
    let mut conv: MixedIntFloat = MixedIntFloat { f: n };
    unsafe {
        conv.i = 0x5f3759df - (conv.i >> 1);
        conv.f *= 1.5f32 - (n * 0.5f32 * conv.f * conv.f);
        conv.f
    }
}