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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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18
arch/alpha/include/asm/bitops.h
View file

@ -405,29 +405,31 @@ static inline int fls(int x)
#if defined(CONFIG_ALPHA_EV6) && defined(CONFIG_ALPHA_EV67)
/* Whee. EV67 can calculate it directly. */
static inline unsigned long hweight64(unsigned long w)
static inline unsigned long __arch_hweight64(unsigned long w)
{
return __kernel_ctpop(w);
}
static inline unsigned int hweight32(unsigned int w)
static inline unsigned int __arch_weight32(unsigned int w)
{
return hweight64(w);
return __arch_hweight64(w);
}
static inline unsigned int hweight16(unsigned int w)
static inline unsigned int __arch_hweight16(unsigned int w)
{
return hweight64(w & 0xffff);
return __arch_hweight64(w & 0xffff);
}
static inline unsigned int hweight8(unsigned int w)
static inline unsigned int __arch_hweight8(unsigned int w)
{
return hweight64(w & 0xff);
return __arch_hweight64(w & 0xff);
}
#else
#include <asm-generic/bitops/hweight.h>
#include <asm-generic/bitops/arch_hweight.h>
#endif
#include <asm-generic/bitops/const_hweight.h>
#endif /* __KERNEL__ */
#include <asm-generic/bitops/find.h>

11
arch/ia64/include/asm/bitops.h
View file

@ -437,17 +437,18 @@ __fls (unsigned long x)
* hweightN: returns the hamming weight (i.e. the number
* of bits set) of a N-bit word
*/
static __inline__ unsigned long
hweight64 (unsigned long x)
static __inline__ unsigned long __arch_hweight64(unsigned long x)
{
unsigned long result;
result = ia64_popcnt(x);
return result;
}
#define hweight32(x) (unsigned int) hweight64((x) & 0xfffffffful)
#define hweight16(x) (unsigned int) hweight64((x) & 0xfffful)
#define hweight8(x) (unsigned int) hweight64((x) & 0xfful)
#define __arch_hweight32(x) ((unsigned int) __arch_hweight64((x) & 0xfffffffful))
#define __arch_hweight16(x) ((unsigned int) __arch_hweight64((x) & 0xfffful))
#define __arch_hweight8(x) ((unsigned int) __arch_hweight64((x) & 0xfful))
#include <asm-generic/bitops/const_hweight.h>
#endif /* __KERNEL__ */

11
arch/sparc/include/asm/bitops_64.h
View file

@ -44,7 +44,7 @@ extern void change_bit(unsigned long nr, volatile unsigned long *addr);
#ifdef ULTRA_HAS_POPULATION_COUNT
static inline unsigned int hweight64(unsigned long w)
static inline unsigned int __arch_hweight64(unsigned long w)
{
unsigned int res;
@ -52,7 +52,7 @@ static inline unsigned int hweight64(unsigned long w)
return res;
}
static inline unsigned int hweight32(unsigned int w)
static inline unsigned int __arch_hweight32(unsigned int w)
{
unsigned int res;
@ -60,7 +60,7 @@ static inline unsigned int hweight32(unsigned int w)
return res;
}
static inline unsigned int hweight16(unsigned int w)
static inline unsigned int __arch_hweight16(unsigned int w)
{
unsigned int res;
@ -68,7 +68,7 @@ static inline unsigned int hweight16(unsigned int w)
return res;
}
static inline unsigned int hweight8(unsigned int w)
static inline unsigned int __arch_hweight8(unsigned int w)
{
unsigned int res;
@ -78,9 +78,10 @@ static inline unsigned int hweight8(unsigned int w)
#else
#include <asm-generic/bitops/hweight.h>
#include <asm-generic/bitops/arch_hweight.h>
#endif
#include <asm-generic/bitops/const_hweight.h>
#include <asm-generic/bitops/lock.h>
#endif /* __KERNEL__ */

11
include/asm-generic/bitops/arch_hweight.h Normal file
View file

@ -0,0 +1,11 @@
#ifndef _ASM_GENERIC_BITOPS_ARCH_HWEIGHT_H_
#define _ASM_GENERIC_BITOPS_ARCH_HWEIGHT_H_
#include <asm/types.h>
extern unsigned int __arch_hweight32(unsigned int w);
extern unsigned int __arch_hweight16(unsigned int w);
extern unsigned int __arch_hweight8(unsigned int w);
extern unsigned long __arch_hweight64(__u64 w);
#endif /* _ASM_GENERIC_BITOPS_HWEIGHT_H_ */

42
include/asm-generic/bitops/const_hweight.h Normal file
View file

@ -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_ */

8
include/asm-generic/bitops/hweight.h
View file

@ -1,11 +1,7 @@
#ifndef _ASM_GENERIC_BITOPS_HWEIGHT_H_
#define _ASM_GENERIC_BITOPS_HWEIGHT_H_
#include <asm/types.h>
extern unsigned int hweight32(unsigned int w);
extern unsigned int hweight16(unsigned int w);
extern unsigned int hweight8(unsigned int w);
extern unsigned long hweight64(__u64 w);
#include <asm-generic/bitops/arch_hweight.h>
#include <asm-generic/bitops/const_hweight.h>
#endif /* _ASM_GENERIC_BITOPS_HWEIGHT_H_ */

25
include/linux/bitops.h
View file

@ -47,31 +47,6 @@ static inline unsigned long hweight_long(unsigned long w)
return sizeof(w) == 4 ? hweight32(w) : hweight64(w);
}
/*
* Clearly slow versions of the hweightN() functions, their benefit is
* of course compile time evaluation of constant arguments.
*/
#define HWEIGHT8(w) \
( BUILD_BUG_ON_ZERO(!__builtin_constant_p(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 HWEIGHT16(w) (HWEIGHT8(w) + HWEIGHT8((w) >> 8))
#define HWEIGHT32(w) (HWEIGHT16(w) + HWEIGHT16((w) >> 16))
#define HWEIGHT64(w) (HWEIGHT32(w) + HWEIGHT32((w) >> 32))
/*
* Type invariant version that simply casts things to the
* largest type.
*/
#define HWEIGHT(w) HWEIGHT64((u64)(w))
/**
* rol32 - rotate a 32-bit value left
* @word: value to rotate

19
lib/hweight.c
View file

@ -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);