[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>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/asm-x86_64/bitops.h b/include/asm-x86_64/bitops.h
index f7ba57b1cc08..5b535eaf5309 100644
--- a/include/asm-x86_64/bitops.h
+++ b/include/asm-x86_64/bitops.h
@@ -399,6 +399,8 @@ static __inline__ int fls(int x)
         return r+1;
 }
 
+#define ARCH_HAS_FAST_MULTIPLIER 1
+
 #include <asm-generic/bitops/hweight.h>
 
 #endif /* __KERNEL__ */