mirror of
https://github.com/torvalds/linux
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39d997b514
Optimize hweight32 by using the same technique in hweight64.
The proof of this technique can be found in the commit log for
f9b4192923 ("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>
66 lines
1.8 KiB
C
66 lines
1.8 KiB
C
#include <linux/module.h>
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#include <linux/bitops.h>
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#include <asm/types.h>
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/**
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* hweightN - returns the hamming weight of a N-bit word
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* @x: the word to weigh
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*
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* The Hamming Weight of a number is the total number of bits set in it.
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*/
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unsigned int hweight32(unsigned int w)
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{
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#ifdef ARCH_HAS_FAST_MULTIPLIER
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w -= (w >> 1) & 0x55555555;
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w = (w & 0x33333333) + ((w >> 2) & 0x33333333);
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w = (w + (w >> 4)) & 0x0f0f0f0f;
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return (w * 0x01010101) >> 24;
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#else
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unsigned int res = w - ((w >> 1) & 0x55555555);
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res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
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res = (res + (res >> 4)) & 0x0F0F0F0F;
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res = res + (res >> 8);
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return (res + (res >> 16)) & 0x000000FF;
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#endif
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}
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EXPORT_SYMBOL(hweight32);
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unsigned int hweight16(unsigned int w)
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{
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unsigned int res = w - ((w >> 1) & 0x5555);
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res = (res & 0x3333) + ((res >> 2) & 0x3333);
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res = (res + (res >> 4)) & 0x0F0F;
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return (res + (res >> 8)) & 0x00FF;
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}
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EXPORT_SYMBOL(hweight16);
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unsigned int hweight8(unsigned int w)
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{
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unsigned int res = w - ((w >> 1) & 0x55);
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res = (res & 0x33) + ((res >> 2) & 0x33);
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return (res + (res >> 4)) & 0x0F;
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}
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EXPORT_SYMBOL(hweight8);
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unsigned long hweight64(__u64 w)
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{
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#if BITS_PER_LONG == 32
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return hweight32((unsigned int)(w >> 32)) + hweight32((unsigned int)w);
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#elif BITS_PER_LONG == 64
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#ifdef ARCH_HAS_FAST_MULTIPLIER
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w -= (w >> 1) & 0x5555555555555555ul;
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w = (w & 0x3333333333333333ul) + ((w >> 2) & 0x3333333333333333ul);
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w = (w + (w >> 4)) & 0x0f0f0f0f0f0f0f0ful;
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return (w * 0x0101010101010101ul) >> 56;
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#else
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__u64 res = w - ((w >> 1) & 0x5555555555555555ul);
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res = (res & 0x3333333333333333ul) + ((res >> 2) & 0x3333333333333333ul);
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res = (res + (res >> 4)) & 0x0F0F0F0F0F0F0F0Ful;
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res = res + (res >> 8);
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res = res + (res >> 16);
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return (res + (res >> 32)) & 0x00000000000000FFul;
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#endif
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#endif
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}
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EXPORT_SYMBOL(hweight64);
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