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bitops: Optimize hweight() by making use of compile-time evaluation

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Rename the extisting runtime hweight() implementations to
__arch_hweight(), rename the compile-time versions to __const_hweight()
and then have hweight() pick between them.

Suggested-by: H. Peter Anvin <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
LKML-Reference: <20100318111929.GB11152@aftab>
Acked-by: H. Peter Anvin <[email protected]>
LKML-Reference: <1265028224.24455.154.camel@laptop>
Signed-off-by: H. Peter Anvin <[email protected]>
This commit is contained in:
Peter Zijlstra 2010-02-01 15:03:07 +01:00 • committed by H. Peter Anvin
commit 1527bc8b92
8 changed files with 87 additions and 58 deletions
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19
lib/hweight.c
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@ -9,7 +9,7 @@
* The Hamming Weight of a number is the total number of bits set in it.
*/
unsigned int hweight32(unsigned int w)
unsigned int __arch_hweight32(unsigned int w)
{
#ifdef ARCH_HAS_FAST_MULTIPLIER
w -= (w >> 1) & 0x55555555;
@ -24,29 +24,30 @@ unsigned int hweight32(unsigned int w)
return (res + (res >> 16)) & 0x000000FF;
#endif
}
EXPORT_SYMBOL(hweight32);
EXPORT_SYMBOL(__arch_hweight32);
unsigned int hweight16(unsigned int w)
unsigned int __arch_hweight16(unsigned int w)
{
unsigned int res = w - ((w >> 1) & 0x5555);
res = (res & 0x3333) + ((res >> 2) & 0x3333);
res = (res + (res >> 4)) & 0x0F0F;
return (res + (res >> 8)) & 0x00FF;
}
EXPORT_SYMBOL(hweight16);
EXPORT_SYMBOL(__arch_hweight16);
unsigned int hweight8(unsigned int w)
unsigned int __arch_hweight8(unsigned int w)
{
unsigned int res = w - ((w >> 1) & 0x55);
res = (res & 0x33) + ((res >> 2) & 0x33);
return (res + (res >> 4)) & 0x0F;
}
EXPORT_SYMBOL(hweight8);
EXPORT_SYMBOL(__arch_hweight8);
unsigned long hweight64(__u64 w)
unsigned long __arch_hweight64(__u64 w)
{
#if BITS_PER_LONG == 32
return hweight32((unsigned int)(w >> 32)) + hweight32((unsigned int)w);
return __arch_hweight32((unsigned int)(w >> 32)) +
__arch_hweight32((unsigned int)w);
#elif BITS_PER_LONG == 64
#ifdef ARCH_HAS_FAST_MULTIPLIER
w -= (w >> 1) & 0x5555555555555555ul;
@ -63,4 +64,4 @@ unsigned long hweight64(__u64 w)
#endif
#endif
}
EXPORT_SYMBOL(hweight64);
EXPORT_SYMBOL(__arch_hweight64);