From: Eric Dumazet Date: Tue, 29 Apr 2008 07:58:35 +0000 (-0700) Subject: Avoid divides in BITS_TO_LONGS X-Git-Tag: v2.6.26-rc1~677 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ede9c697bc7513f210103fa77a9031e89726ae40;p=linux-2.6 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/include/linux/bitops.h b/include/linux/bitops.h index 48bde600a2..8340a3aba4 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 /*