Commit-ID: 39d997b514e12d5aff0dca206eb8996b3957927e Gitweb: http://git.kernel.org/tip/39d997b514e12d5aff0dca206eb8996b3957927e Author: Akinobu Mita <akinobu.mita@xxxxxxxxx> AuthorDate: Mon, 21 Dec 2009 16:20:16 -0800 Committer: Ingo Molnar <mingo@xxxxxxx> CommitDate: Mon, 28 Dec 2009 10:41:39 +0100 x86, core: Optimize hweight32() Optimize hweight32 by using the same technique in hweight64. The proof of this technique can be found in the commit log for f9b4192923fa6e38331e88214b1fe5fc21583fcc ("bitops: hweight() speedup"). The userspace benchmark on x86_32 showed 20% speedup with bitmap_weight() which uses hweight32 to count bits for each unsigned long on 32bit architectures. int main(void) { #define SZ (1024 * 1024 * 512) static DECLARE_BITMAP(bitmap, SZ) = { [0 ... 100] = 1, }; return bitmap_weight(bitmap, SZ); } Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> LKML-Reference: <1258603932-4590-1-git-send-email-akinobu.mita@xxxxxxxxx> [ only x86 sets ARCH_HAS_FAST_MULTIPLIER so we do this via the x86 tree] Signed-off-by: Ingo Molnar <mingo@xxxxxxx> --- lib/hweight.c | 7 +++++++ 1 files changed, 7 insertions(+), 0 deletions(-) diff --git a/lib/hweight.c b/lib/hweight.c index 389424e..63ee4eb 100644 --- a/lib/hweight.c +++ b/lib/hweight.c @@ -11,11 +11,18 @@ unsigned int hweight32(unsigned int w) { +#ifdef ARCH_HAS_FAST_MULTIPLIER + w -= (w >> 1) & 0x55555555; + w = (w & 0x33333333) + ((w >> 2) & 0x33333333); + w = (w + (w >> 4)) & 0x0f0f0f0f; + return (w * 0x01010101) >> 24; +#else unsigned int res = w - ((w >> 1) & 0x55555555); res = (res & 0x33333333) + ((res >> 2) & 0x33333333); res = (res + (res >> 4)) & 0x0F0F0F0F; res = res + (res >> 8); return (res + (res >> 16)) & 0x000000FF; +#endif } EXPORT_SYMBOL(hweight32); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html