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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 <hpa@zytor.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100318111929.GB11152@aftab>
Acked-by: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <1265028224.24455.154.camel@laptop>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Peter Zijlstra
2010-02-01 15:03:07 +01:00
committed by H. Peter Anvin
parent 0fdf86754f
commit 1527bc8b92
8 changed files with 87 additions and 58 deletions
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42
include/asm-generic/bitops/const_hweight.h Normal file
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@@ -0,0 +1,42 @@
#ifndef _ASM_GENERIC_BITOPS_CONST_HWEIGHT_H_
#define _ASM_GENERIC_BITOPS_CONST_HWEIGHT_H_
/*
* Compile time versions of __arch_hweightN()
*/
#define __const_hweight8(w) \
( (!!((w) & (1ULL << 0))) + \
(!!((w) & (1ULL << 1))) + \
(!!((w) & (1ULL << 2))) + \
(!!((w) & (1ULL << 3))) + \
(!!((w) & (1ULL << 4))) + \
(!!((w) & (1ULL << 5))) + \
(!!((w) & (1ULL << 6))) + \
(!!((w) & (1ULL << 7))) )
#define __const_hweight16(w) (__const_hweight8(w) + __const_hweight8((w) >> 8 ))
#define __const_hweight32(w) (__const_hweight16(w) + __const_hweight16((w) >> 16))
#define __const_hweight64(w) (__const_hweight32(w) + __const_hweight32((w) >> 32))
/*
* Generic interface.
*/
#define hweight8(w) (__builtin_constant_p(w) ? __const_hweight8(w) : __arch_hweight8(w))
#define hweight16(w) (__builtin_constant_p(w) ? __const_hweight16(w) : __arch_hweight16(w))
#define hweight32(w) (__builtin_constant_p(w) ? __const_hweight32(w) : __arch_hweight32(w))
#define hweight64(w) (__builtin_constant_p(w) ? __const_hweight64(w) : __arch_hweight64(w))
/*
* Interface for known constant arguments
*/
#define HWEIGHT8(w) (BUILD_BUG_ON_ZERO(!__builtin_constant_p(w)) + __const_hweight8(w))
#define HWEIGHT16(w) (BUILD_BUG_ON_ZERO(!__builtin_constant_p(w)) + __const_hweight16(w))
#define HWEIGHT32(w) (BUILD_BUG_ON_ZERO(!__builtin_constant_p(w)) + __const_hweight32(w))
#define HWEIGHT64(w) (BUILD_BUG_ON_ZERO(!__builtin_constant_p(w)) + __const_hweight64(w))
/*
* Type invariant interface to the compile time constant hweight functions.
*/
#define HWEIGHT(w) HWEIGHT64((u64)w)
#endif /* _ASM_GENERIC_BITOPS_CONST_HWEIGHT_H_ */