diff options
| author | Andi Kleen <ak@suse.de> | 2006-09-26 10:52:38 +0200 |
|---|---|---|
| committer | Andi Kleen <andi@basil.nowhere.org> | 2006-09-26 10:52:38 +0200 |
| commit | 0136611c62e8650e354b95c76dff6d2ce6030eff (patch) | |
| tree | 9ba66105bccc4d83b84663b8dda7e51962c22a04 /lib/hweight.c | |
| parent | 8380aabb99719af583447133f19a4d8074b5c337 (diff) | |
| download | lwn-0136611c62e8650e354b95c76dff6d2ce6030eff.tar.gz lwn-0136611c62e8650e354b95c76dff6d2ce6030eff.zip | |
[PATCH] optimize hweight64 for x86_64
Based on patch from David Rientjes <rientjes@google.com>, but
changed by AK.
Optimizes the 64-bit hamming weight for x86_64 processors assuming they
have fast multiplication. Uses five fewer bitops than the generic
hweight64. Benchmark on one EMT64 showed ~25% speedup with 2^24
consecutive calls.
Define a new ARCH_HAS_FAST_MULTIPLIER that can be set by other
architectures that can also multiply fast.
Signed-off-by: Andi Kleen <ak@suse.de>
Diffstat (limited to 'lib/hweight.c')
| -rw-r--r-- | lib/hweight.c | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/lib/hweight.c b/lib/hweight.c index 438257671708..360556a7803d 100644 --- a/lib/hweight.c +++ b/lib/hweight.c @@ -1,5 +1,6 @@ #include <linux/module.h> #include <asm/types.h> +#include <asm/bitops.h> /** * hweightN - returns the hamming weight of a N-bit word @@ -40,14 +41,19 @@ unsigned long hweight64(__u64 w) #if BITS_PER_LONG == 32 return hweight32((unsigned int)(w >> 32)) + hweight32((unsigned int)w); #elif BITS_PER_LONG == 64 +#ifdef ARCH_HAS_FAST_MULTIPLIER + w -= (w >> 1) & 0x5555555555555555ul; + w = (w & 0x3333333333333333ul) + ((w >> 2) & 0x3333333333333333ul); + w = (w + (w >> 4)) & 0x0f0f0f0f0f0f0f0ful; + return (w * 0x0101010101010101ul) >> 56; +#else __u64 res = w - ((w >> 1) & 0x5555555555555555ul); res = (res & 0x3333333333333333ul) + ((res >> 2) & 0x3333333333333333ul); res = (res + (res >> 4)) & 0x0F0F0F0F0F0F0F0Ful; res = res + (res >> 8); res = res + (res >> 16); return (res + (res >> 32)) & 0x00000000000000FFul; -#else -#error BITS_PER_LONG not defined +#endif #endif } EXPORT_SYMBOL(hweight64); |