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    Subject[tip:core/hweight] bitops: Optimize hweight() by making use of compile-time evaluation
    Commit-ID:  1527bc8b928dd1399c3d3467dd47d9ede210978a
    Gitweb: http://git.kernel.org/tip/1527bc8b928dd1399c3d3467dd47d9ede210978a
    Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
    AuthorDate: Mon, 1 Feb 2010 15:03:07 +0100
    Committer: H. Peter Anvin <hpa@zytor.com>
    CommitDate: Tue, 6 Apr 2010 15:52:11 -0700

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

    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>
    ---
    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(-)

    diff --git a/arch/alpha/include/asm/bitops.h b/arch/alpha/include/asm/bitops.h
    index 15f3ae2..296da1d 100644
    --- a/arch/alpha/include/asm/bitops.h
    +++ b/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>
    diff --git a/arch/ia64/include/asm/bitops.h b/arch/ia64/include/asm/bitops.h
    index 6ebc229..9da3df6 100644
    --- a/arch/ia64/include/asm/bitops.h
    +++ b/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__ */

    diff --git a/arch/sparc/include/asm/bitops_64.h b/arch/sparc/include/asm/bitops_64.h
    index e72ac9c..766121a 100644
    --- a/arch/sparc/include/asm/bitops_64.h
    +++ b/arch/sparc/include/asm/bitops_64.h
    @@ -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__ */

    diff --git a/include/asm-generic/bitops/arch_hweight.h b/include/asm-generic/bitops/arch_hweight.h
    new file mode 100644
    index 0000000..3a7be84
    --- /dev/null
    +++ b/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_ */
    diff --git a/include/asm-generic/bitops/const_hweight.h b/include/asm-generic/bitops/const_hweight.h
    new file mode 100644
    index 0000000..fa2a50b
    --- /dev/null
    +++ b/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_ */
    diff --git a/include/asm-generic/bitops/hweight.h b/include/asm-generic/bitops/hweight.h
    index fbbc383..a94d651 100644
    --- a/include/asm-generic/bitops/hweight.h
    +++ b/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_ */
    diff --git a/include/linux/bitops.h b/include/linux/bitops.h
    index b793898..c55d5bc 100644
    --- a/include/linux/bitops.h
    +++ b/include/linux/bitops.h
    @@ -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
    diff --git a/lib/hweight.c b/lib/hweight.c
    index 63ee4eb..a6927e7 100644
    --- a/lib/hweight.c
    +++ b/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);

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