fn montgomery_reduce_matches_from_bytes_mod_order_wide()

in src/scalar.rs [1605:1637]

• 22 lines of code
• 2 McCabe index (conditional complexity)

    fn montgomery_reduce_matches_from_bytes_mod_order_wide() {
        let mut bignum = [0u8; 64];

        // set bignum = x + 2^256x
        for i in 0..32 {
            bignum[   i] = X[i];
            bignum[32+i] = X[i];
        }
        // x + 2^256x (mod l)
        //         = 3958878930004874126169954872055634648693766179881526445624823978500314864344
        let expected = Scalar{
            bytes: [
                216, 154, 179, 139, 210, 121,   2,  71,
                 69,  99, 158, 216,  23, 173,  63, 100,
                204,   0,  91,  50, 219, 153,  57, 249,
                 28,  82,  31, 197, 100, 165, 192,   8
            ],
        };
        let reduced = Scalar::from_bytes_mod_order_wide(&bignum);

        // The reduced scalar should match the expected
        assert_eq!(reduced.bytes, expected.bytes);

        //  (x + 2^256x) * R
        let interim = UnpackedScalar::mul_internal(&UnpackedScalar::from_bytes_wide(&bignum),
                                                   &constants::R);
        // ((x + 2^256x) * R) / R  (mod l)
        let montgomery_reduced = UnpackedScalar::montgomery_reduce(&interim);

        // The Montgomery reduced scalar should match the reduced one, as well as the expected
        assert_eq!(montgomery_reduced.0, reduced.unpack().0);
        assert_eq!(montgomery_reduced.0, expected.unpack().0)
    }