http://www.matrix67.com/data/InvSqrt.pdf

sqrt.rs

fn my_sqrt(x: i32) -> i32 {
    let mut n = x as f64;
    let half = 0.5 * n;
    let mut i = unsafe {
        std::mem::transmute::<f64, i64>(n)
    };
    i = 0x5fe6ec85e7de30da - (i>>1);
    n = unsafe{
        std::mem::transmute::<i64, f64>(i)
    };
    for i in 0..3 {
        n = n*(1.5-half*n*n);
    }
    return (1.0/n) as i32;
}