Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755932AbZDWRol (ORCPT ); Thu, 23 Apr 2009 13:44:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752891AbZDWRoc (ORCPT ); Thu, 23 Apr 2009 13:44:32 -0400 Received: from astoria.ccjclearline.com ([64.235.106.9]:36419 "EHLO astoria.ccjclearline.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753341AbZDWRob (ORCPT ); Thu, 23 Apr 2009 13:44:31 -0400 Date: Thu, 23 Apr 2009 13:43:34 -0400 (EDT) From: "Robert P. J. Day" X-X-Sender: rpjday@localhost.localdomain To: Linux Kernel Mailing List cc: Andrew Morton Subject: [PATCH] Introduce a boolean "single_bit_set" function. Message-ID: User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - astoria.ccjclearline.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - crashcourse.ca X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1702 Lines: 50 A boolean single_bit_set() routine would simplify the numerous constructs of the form (((n & (n - 1)) == 0)) when testing for single-bitness. Signed-off-by: Robert P. J. Day --- This is similar to the current is_power_of_2() routine defined in include/linux/log2.h, which is mathematically identical but, semantically, should be defined independently just so the code is more readable. I'm open to an alternative function name. diff --git a/include/linux/bitops.h b/include/linux/bitops.h index 6182913..1c0c840 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -45,6 +45,13 @@ static inline unsigned long hweight_long(unsigned long w) return sizeof(w) == 4 ? hweight32(w) : hweight64(w); } +static inline __attribute__((const)) +bool single_bit_set(unsigned long n) +{ + return (n != 0 && ((n & (n - 1)) == 0)); +} + + /** * rol32 - rotate a 32-bit value left * @word: value to rotate ======================================================================== Robert P. J. Day Waterloo, Ontario, CANADA Linux Consulting, Training and Annoying Kernel Pedantry. Web page: http://crashcourse.ca Linked In: http://www.linkedin.com/in/rpjday Twitter: http://twitter.com/rpjday ======================================================================== -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/