@geofflangdale@mastodon.social
Post #2252119
2026-05-06 01:18 UTC
@synlogic4242@social.vivaldi.net @regehr@mastodon.social To be honest, googling anything in SSE4.2 but CRC32 (why is this SSE4.2? who knows?) and PCMPGTQ (a 64b lanewise greater-than comparison, peculiarly absent previously) is mostly a waste of time.
There are still some uses of the PCMP* string matching instructions - particularly on 16b quantities and in the context where you don't know either side of the comparison well in advance - but they have the dubious distinction of being obsolete for much of their intended use ...
Replies (1)
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@geofflangdale@mastodon.social 2026-05-06 01:20
@synlogic4242@social.vivaldi.net @regehr@mastodon.social at the time they were delivered. Due to the fact that these instructions are quite unloved, they were not promoted to 256b in AVX2, much less 512b, so they have become even less competitive, but they were *never* competitive against the PSHUFB-table approach for most of the 'we're looking for a known-in-advance table of characters' use cases. Never. I guess I *did* just write the TIWWW article in your mentions, sorry.