I'm not sure if you're implying this is premature optimisation. It isn't.
It's a performance-sensitive standard-library function, the kind of thing that deserves optimisation in assembly. It's also the kind of problem that can be accelerated with SIMD, but that necessarily means more complex code. That's why the standard library implementations aren't always dead simple.
Here's a pretty in-depth discussion [0]. They discuss CPU throttling, caches, and being memory-bound.
It's a performance-sensitive standard-library function, the kind of thing that deserves optimisation in assembly. It's also the kind of problem that can be accelerated with SIMD, but that necessarily means more complex code. That's why the standard library implementations aren't always dead simple.
Here's a pretty in-depth discussion [0]. They discuss CPU throttling, caches, and being memory-bound.
[0] https://news.ycombinator.com/item?id=18260154