Writing clean C loops are a good way of writing vectorized code. Checking the vectorization report of icc 2018 for fprop() shows that the loops got inlined, un

Writing clean C loops are a good way of writing vectorized code. Checking the vectorization report of icc 2018 for fprop() shows that the loops got inlined, unrolled and vectorized (with AVX512 and AVX2 instructions using XMM/YMM registers). I doubt that doing it by hand would be faster, but it would make the code a lot more complex. You have a point on the parallelization part though, it can be cleanly parallelized with a few OpenMP Pragmas.