Wow, those examples took me a while to go through and understand; it's amazing the level you can optimize a piece of code to hardware. I'm curious to benchmark the implementations and see the performance difference.

Maybe you or someone else knows the answer to this though: it seems like they are processing 4 bytes of the string at a time. If they read over (i.e. the NULL byte is in byte position 1 2 or 3), isn't that technically undefined behavior? They are only reading in the memory, but I feel like valgrind or another tool would spit out an error if that happened. It's aligned, so it won't trigger a page fault, but it seems like an unsafe optimization.