From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751980AbXCGPxd (ORCPT ); Wed, 7 Mar 2007 10:53:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751998AbXCGPxd (ORCPT ); Wed, 7 Mar 2007 10:53:33 -0500 Received: from raven.upol.cz ([158.194.120.4]:40560 "EHLO raven.upol.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751980AbXCGPxc (ORCPT ); Wed, 7 Mar 2007 10:53:32 -0500 To: David Howells Cc: Linus Torvalds , Al Viro , akpm@linux-foundation.org, benh@kernel.crashing.org, linux-kernel@vger.kernel.org, hpa@zytor.com, johannes@sipsolutions.net Subject: ALIGN via ilog2 without gccisms (Re: [PATCH] Fix get_order()) In-Reply-To: <8543.1173267786@redhat.com> References: <20070306173929.2708.37191.stgit@warthog.cambridge.redhat.com> <8543.1173267786@redhat.com> Date: Wed, 7 Mar 2007 17:02:53 +0100 Message-Id: From: Oleg Verych Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > From: David Howells > Newsgroups: gmane.linux.kernel > Subject: Re: [PATCH] Fix get_order() > Date: Wed, 07 Mar 2007 11:43:06 +0000 > [] > Various archs (including i386, x86_64, powerpc and frv) have instructions that > can be used to calculate integer log2(N). > Probably it can be used to get rid of gccisms and "type fluff" due to bitwise arithmetics in ALIGN? Here: #define ALIGN(x,a) __ALIGN_MASK(x,(typeof(x))(a)-1) #define __ALIGN_MASK(x,mask) (((x)+(mask))&~(mask)) like that: #define ALIGN(x,y) __ALIGN_MASK(x,ilog2(y)) #define __ALIGN_MASK(x,bits) (((((x) >> (bits)) << 1) + 2) << (bits - 1)) Note side effect, that this one always yields even result. Maybe this is good, due to avoidance of misaligned access. ____