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| author | Akinobu Mita <akinobu.mita@gmail.com> | 2009-12-21 16:20:16 -0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-12-28 10:41:39 +0100 |
| commit | 39d997b514e12d5aff0dca206eb8996b3957927e (patch) | |
| tree | d63202847a8a421fbd1fc39e9a2433dbc86ce104 | |
| parent | 6b7b284958d47b77d06745b36bc7f36dab769d9b (diff) | |
| download | lwn-39d997b514e12d5aff0dca206eb8996b3957927e.tar.gz lwn-39d997b514e12d5aff0dca206eb8996b3957927e.zip | |
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@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <1258603932-4590-1-git-send-email-akinobu.mita@gmail.com>
[ only x86 sets ARCH_HAS_FAST_MULTIPLIER so we do this via the x86 tree]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
| -rw-r--r-- | lib/hweight.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/lib/hweight.c b/lib/hweight.c index 389424ecb129..63ee4eb1228d 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); |