Ten Ways to Check if an Integer Is a Power Of Two in C

Re:Ten Ways to Check if an Integer Is a Power Of Two in C by dasmoth on Tuesday July 26, 2011 @11:40AM (#2807829)

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.

[ Parent | on HN ]

Re:Ten Ways to Check if an Integer Is a Power Of Two in C by neckbeard on Tuesday July 26, 2011 @07:29PM (#2809961)

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

[ Parent | on HN ]