Function compute_n_prime_newton 

pub fn compute_n_prime_newton<T>(modulus: T, w: usize) -> T
where
    T: Copy + One + Zero + WrappingMul + WrappingSub + WrappingAdd,

Newton’s method for N’ = -N^{-1} mod 2^W.

Invariant: after each iteration, modulus * x ≡ 1 (mod 2^precision). We return 0 - x so that modulus * N' ≡ -1 (mod 2^W).