Messages in this thread Patch in this message | | | From | Akinobu Mita <> | Subject | [PATCH] Optimize hweight32 for x86 | Date | Thu, 19 Nov 2009 13:12:12 +0900 |
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Optimize hweight32 by using the same technique in hweight64. The proof of this technique can be found in the commit log for f9b4192923fa6e38331e88214b1fe5fc21583fcc
The userspece 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@gmail.com> --- 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); -- 1.6.5.1
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