This was written by Chris "skeeto" Wellons, a computer scientist for which I've personally grown a lot of admiration. Check out his Github if you're interested, he does a lot of really interesting things and is worth following.

Personal favorite is the branchless utf-8 decoder which I've used quite a few times in lexers and other projects.

https://github.com/skeeto?tab=repositories&sort=stargazers