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

Peter Zijlstra
2010-02-04T10:27:26Z

Hi Andrew,

Ingo suggested you take this patch through -mm since it touches !x86
arch bits.

It should apply nicely once fce877e3a429940a986e085a41e8b57f2d922e36
makes in into -next.

---
Subject: bitops: Optimize hweight() by making use of compile-time evaluation
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Mon Feb 01 15:03:07 CET 2010

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>
Acked-by: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <1265028224.24455.154.camel@laptop>
---
arch/alpha/include/asm/bitops.h | 18 ++++++------
arch/ia64/include/asm/bitops.h | 11 ++++---
arch/sparc/include/asm/bitops_64.h | 11 ++++---
include/asm-generic/bitops/arch_hweight.h | 11 +++++++
include/asm-generic/bitops/const_hweight.h | 42 +++++++++++++++++++++++++++++
include/asm-generic/bitops/hweight.h | 8 +----
include/linux/bitops.h | 25 -----------------
lib/hweight.c | 19 ++++++-------
8 files changed, 87 insertions(+), 58 deletions(-)

Index: linux-2.6/arch/alpha/include/asm/bitops.h
===================================================================
--- linux-2.6.orig/arch/alpha/include/asm/bitops.h
+++ linux-2.6/arch/alpha/include/asm/bitops.h
@@ -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>
Index: linux-2.6/arch/ia64/include/asm/bitops.h
===================================================================
--- linux-2.6.orig/arch/ia64/include/asm/bitops.h
+++ linux-2.6/arch/ia64/include/asm/bitops.h
@@ -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__ */

Index: linux-2.6/arch/sparc/include/asm/bitops_64.h
===================================================================
--- linux-2.6.orig/arch/sparc/include/asm/bitops_64.h
+++ linux-2.6/arch/sparc/include/asm/bitops_64.h
@@ -44,7 +44,7 @@ extern void change_bit(unsigned long nr,

#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(uns
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(uns
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(uns
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(unsi

#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__ */

Index: linux-2.6/include/asm-generic/bitops/arch_hweight.h
===================================================================
--- /dev/null
+++ linux-2.6/include/asm-generic/bitops/arch_hweight.h
@@ -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_ */
Index: linux-2.6/include/asm-generic/bitops/const_hweight.h
===================================================================
--- /dev/null
+++ linux-2.6/include/asm-generic/bitops/const_hweight.h
@@ -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_ */
Index: linux-2.6/include/asm-generic/bitops/hweight.h
===================================================================
--- linux-2.6.orig/include/asm-generic/bitops/hweight.h
+++ linux-2.6/include/asm-generic/bitops/hweight.h
@@ -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_ */
Index: linux-2.6/include/linux/bitops.h
===================================================================
--- linux-2.6.orig/include/linux/bitops.h
+++ linux-2.6/include/linux/bitops.h
@@ -45,31 +45,6 @@ static inline unsigned long hweight_long
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
Index: linux-2.6/lib/hweight.c
===================================================================
--- linux-2.6.orig/lib/hweight.c
+++ linux-2.6/lib/hweight.c
@@ -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);