linux-kernel - [PATCH] Avoid divides in BITS_TO

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Date:	Thu, 07 Feb 2008 08:54:29 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Linux kernel <linux-kernel@...r.kernel.org>
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@...mosbay.com>

View attachment "BITS_TO_LONGS.patch" of type "text/plain" (473 bytes)