Messages in this thread Patch in this message | | | Date | Thu, 07 Feb 2008 08:54:29 +0100 | From | Eric Dumazet <> | Subject | [PATCH] 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>
diff --git a/include/linux/bitops.h b/include/linux/bitops.h index 69c1edb..be5c27c 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 /* | |