Continuing my daily posting of things I've made to try and #GetFediHired, this is a contribution I made to the `bytestring` library to give them a SIMD-optimized UTF-8 validator: https://github.com/haskell/bytestring/blob/master/cbits/is-valid-utf8.c

This was, without a doubt, some of the most challenging code I have ever written in _any_ language. It involved a very complex mixture of concerns, and I had performance targets to hit with it too. Oh, _and_ it had to be self-contained and portable, including to 'no SIMD' platforms!