Unfortunately __builtin_popcnt isn't emitting a popcnt instruction with the GCC ... | Hacker News

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dasmoth on July 26, 2011 | parent | context | favorite | on: Ten Ways to Check if an Integer Is a Power Of Two ...

Unfortunately __builtin_popcnt isn't emitting a popcnt instruction with the GCC I've got here, even using -msse4.2. I believe that very recent GCC does get this right.

neckbeard on July 26, 2011 [–]

GCC 4.4 isn't very recent, but it generates a popcnt with -msse4.2.

GCC 4.5, using popcnt on my Core-i7 860 takes the trivial loop mentioned using "Complement and Compare" from ~10.5s to ~7.5s

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