For example, he uses SIMD in several of these, but one of the performance problems associated with SIMD is the last 'n' bytes. If you processing, say, 16 or 32 bytes at a time, what do you do when you get towards the end of your buffer and that process would over-read past the end of the buffer? Most code I've seen just uses a simple linear process for the last few bytes but this is often very slow. Agner's solution was to just read past the end of the buffer, but use some assembly tricks to ensure there is always valid memory available after the end of the buffer, that way reading past the end of the buffer would (almost) never cause a problem.