A 100LOC C impl of memset, that is faster than glibc's

Re:A 100LOC C impl of memset, that is faster than glibc's by yissp on Friday November 12, 2021 @09:00AM (#29199300)

Is the choice of 16 as the "limit" value based on benchmarking? As opposed to just doing something like "!buffer[0] && !memcmp(buffer, buffer + 1, size - 1)" which uses the same principle.

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Re:A 100LOC C impl of memset, that is faster than glibc's by BeeOnRope on Friday November 12, 2021 @09:24AM (#29199515)

Not the OP, but 16 has the benefit of keeping both pointers in the comparison 16-byte aligned if the buffer was initially aligned.

This would eliminate split loads and provide a decent speedup.

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Re:A 100LOC C impl of memset, that is faster than glibc's by boibombeiro on Saturday November 13, 2021 @03:27AM (#29208339)

This, and loop unrolling, are two commons misconception about uarch optimization.

https://lemire.me/blog/2012/05/31/data-alignment-for-speed-m...

Memory alignment is innocuous (others than often compromise code legibility).

Loop unrolling, on the other hand, can slow down the code. Specially in small loops.

See Agner uarch PDF.

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