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| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2010-01-29 13:25:12 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2010-02-04 09:59:50 +0100 |
| commit | fce877e3a429940a986e085a41e8b57f2d922e36 (patch) | |
| tree | 5bdf6beeda1cfe774dc2a633454bd4d1546e1c08 /include/linux/bitops.h | |
| parent | 8c48e444191de0ff84e85d41180d7bc3e74f14ef (diff) | |
| download | lwn-fce877e3a429940a986e085a41e8b57f2d922e36.tar.gz lwn-fce877e3a429940a986e085a41e8b57f2d922e36.zip | |
bitops: Ensure the compile time HWEIGHT is only used for such
Avoid accidental misuse by failing to compile things
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'include/linux/bitops.h')
| -rw-r--r-- | include/linux/bitops.h | 33 |
1 files changed, 22 insertions, 11 deletions
diff --git a/include/linux/bitops.h b/include/linux/bitops.h index ba0fd1eb4af7..25b8b2f33ae9 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -45,19 +45,30 @@ static inline unsigned long hweight_long(unsigned long w) return sizeof(w) == 4 ? hweight32(w) : hweight64(w); } -#define HWEIGHT8(w) \ - ( (!!((w) & (1ULL << 0))) + \ - (!!((w) & (1ULL << 1))) + \ - (!!((w) & (1ULL << 2))) + \ - (!!((w) & (1ULL << 3))) + \ - (!!((w) & (1ULL << 4))) + \ - (!!((w) & (1ULL << 5))) + \ - (!!((w) & (1ULL << 6))) + \ +/* + * 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)) +#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 |