`memcpy`

Library	Technique
Linux	`rep movs`
Glibc	`movq` pipelined by hand (32 bits)
	`rep movs` for 32 < n < ½L1
	`movq` with prefetching for ½L1 < n < L1
	`movntiq` with prefetching for L1 < n
Musl	`rep movs`

in-the-mood-for-mov/memcpy