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| author | Eric Dumazet <dada1@cosmosbay.com> | 2008-04-29 00:58:35 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-04-29 08:05:59 -0700 |
| commit | ede9c697bc7513f210103fa77a9031e89726ae40 (patch) | |
| tree | a48eaac7da2877aa5600e5b4e99dedabd4b4b6fb /include/linux/bitops.h | |
| parent | cdac75e6f2fec9abc21d0abb4e5d80720eeebb10 (diff) | |
| download | lwn-ede9c697bc7513f210103fa77a9031e89726ae40.tar.gz lwn-ede9c697bc7513f210103fa77a9031e89726ae40.zip | |
Avoid divides in BITS_TO_LONGS
BITS_PER_LONG is a signed value (32 or 64)
DIV_ROUND_UP(nr, BITS_PER_LONG) performs signed arithmetic if "nr" is signed too.
Converting BITS_TO_LONGS(nr) to DIV_ROUND_UP(nr, BITS_PER_BYTE *
sizeof(long)) makes sure compiler can perform a right shift, even if "nr"
is a signed value, instead of an expensive integer divide.
Applying this patch saves 141 bytes on x86 when CONFIG_CC_OPTIMIZE_FOR_SIZE=y
and speedup bitmap operations.
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/bitops.h')
| -rw-r--r-- | include/linux/bitops.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/bitops.h b/include/linux/bitops.h index 48bde600a2db..8340a3aba49a 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -6,8 +6,8 @@ #define BIT(nr) (1UL << (nr)) #define BIT_MASK(nr) (1UL << ((nr) % BITS_PER_LONG)) #define BIT_WORD(nr) ((nr) / BITS_PER_LONG) -#define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_LONG) #define BITS_PER_BYTE 8 +#define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long)) #endif /* |