Comment by ajross

No, that claim is ridiculous. When doing the same task, quite frankly, compilers are much better than any human at optimizing general logic.

But when the human and compiler are not faced with the same problem...

Say, if your compiler doesn't support autovectorization and/or your C code isn't friendly to the idiom, then sure: a 10x difference in performance between a hand-optimized SIMD implementation and a naive scalar one fed to a C compiler is probably about right.