pub fn mul_acc(acc: &mut [u8], symbol: &[u8], coeff: u8)
acc[i] ^= coeff * symbol[i] over GF(2⁸) — the inner loop of RLNC encoding.
acc[i] ^= coeff * symbol[i]
Panics if acc.len() != symbol.len().
acc.len() != symbol.len()