Why is musl slower?
then you look at: https://sourceware.org/git/?p=glibc.git;a=blob;f=string/strl...
and your mind will sort of explode for a bit. The difference is the GLIBC version is dramatically faster; take the comments away and most of us wouldn't even know that's strlen. It's more complex, no question, but it's much faster. GLIBC is full of stuff like that. qsort and memcpy are non-obvious to many folks. It's not complexity for no reason, you'd be challenged to build a better qsort than the one in glibc, it's not easy.
http://ridiculousfish.com/blog/posts/old-age-and-treachery.html
All of those old Unix programs aren't fast by being simple and clean on the inside. Old age and treachery...[1]: https://github.com/bminor/glibc/blob/master/sysdeps/x86_64/s...