From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752444AbbBRWjq (ORCPT ); Wed, 18 Feb 2015 17:39:46 -0500 Received: from mail-lb0-f177.google.com ([209.85.217.177]:42105 "EHLO mail-lb0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751259AbbBRWjp (ORCPT ); Wed, 18 Feb 2015 17:39:45 -0500 From: Rasmus Villemoes To: Andrew Morton , Rasmus Villemoes , Tejun Heo Cc: "George Spelvin" , Yury Norov , linux-kernel@vger.kernel.org Subject: [PATCH] linux/bitmap.h: Improve BITMAP_{LAST,FIRST}_WORD_MASK Date: Wed, 18 Feb 2015 23:39:13 +0100 Message-Id: <1424299153-2210-1-git-send-email-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 2.1.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The macro BITMAP_LAST_WORD_MASK can be implemented without a conditional, which will generally lead to slightly better generated code (221 bytes saved for allmodconfig-GCOV_KERNEL, ~2k with GCOV_KERNEL). As a small bonus, this also ensures that the nbits parameter is expanded exactly once. In BITMAP_FIRST_WORD_MASK, if start is signed gcc is technically allowed to assume it is positive (or divisible by BITS_PER_LONG), and hence just do the simple mask. It doesn't seem to use this, and even on an architecture like x86 where the shift only depends on the lower 5 or 6 bits, and these bits are not affected by the signedness of the expression, gcc still generates code to compute the C99 mandated value of start % BITS_PER_LONG. So just use a mask explicitly, also for consistency with BITMAP_LAST_WORD_MASK. Signed-off-by: Rasmus Villemoes --- include/linux/bitmap.h | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h index dbfbf4990005..be4fa5ddf36c 100644 --- a/include/linux/bitmap.h +++ b/include/linux/bitmap.h @@ -172,12 +172,8 @@ extern unsigned int bitmap_ord_to_pos(const unsigned long *bitmap, unsigned int extern int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp, int nmaskbits); -#define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) % BITS_PER_LONG)) -#define BITMAP_LAST_WORD_MASK(nbits) \ -( \ - ((nbits) % BITS_PER_LONG) ? \ - (1UL<<((nbits) % BITS_PER_LONG))-1 : ~0UL \ -) +#define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1))) +#define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1))) #define small_const_nbits(nbits) \ (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG) -- 2.1.3