the memcopies will of course be compiled to unaligned loads & stores. Clang even seems to simplify the multiplications based on the size of the current portion

the memcopies will of course be compiled to unaligned loads & stores. Clang even seems to simplify the multiplications based on the size of the current portion of the argument, so I don't see much that could be improved. Maybe you could squeeze out a dozen or two percent more speed, but not 3.5x faster.