Function div_rem_knuth 

fn div_rem_knuth<const N: usize>(
    numerator: &[u64; N],
    divisor: &[u64; N],
    n: usize,
    m: usize,
) -> ([u64; N], [u64; N])

Use Knuth Algorithm D to compute numerator / divisor returning the quotient and remainder

n is the number of non-zero 64-bit words in divisor m is the number of non-zero 64-bit words present in numerator beyond divisor, and therefore the number of words in the quotient

A good explanation of the algorithm can be found here