`algorithms/mul_redc`: Do combined multiplication and reduction.

[github-actions[bot]]

On 2022-06-09 @recmo wrote in f0f0ddb “Merge pull request #126 from recmo/redc”:

Do combined multiplication and reduction.

    debug_assert_eq!(b.len(), m.len());
    debug_assert_eq!(result.len(), m.len());
    debug_assert_eq!(inv.wrapping_mul(m[0]), u64::MAX);

    // Compute temp full product.
    // OPT: Do combined multiplication and reduction.
    let mut temp = vec![0; 2 * m.len() + 1];
    mul(a, b, &mut temp);

    // Reduce temp.
    for i in 0..m.len() {

From src/algorithms/mul_redc.rs:13