Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751034AbWA0Gk3 (ORCPT ); Fri, 27 Jan 2006 01:40:29 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751230AbWA0Gk3 (ORCPT ); Fri, 27 Jan 2006 01:40:29 -0500 Received: from ns.miraclelinux.com ([219.118.163.66]:30926 "EHLO mail01.miraclelinux.com") by vger.kernel.org with ESMTP id S1751034AbWA0Gk2 (ORCPT ); Fri, 27 Jan 2006 01:40:28 -0500 Date: Fri, 27 Jan 2006 15:40:34 +0900 To: Balbir Singh Cc: Grant Grundler , Linux Kernel Development , linux-ia64@vger.kernel.org Subject: Re: [PATCH 8/12] generic hweight{32,16,8}() Message-ID: <20060127064034.GB8166@miraclelinux.com> References: <20060125112625.GA18584@miraclelinux.com> <20060125113206.GD18584@miraclelinux.com> <20060125200250.GA26443@flint.arm.linux.org.uk> <20060125205907.GF9995@esmail.cup.hp.com> <20060126032713.GA9984@miraclelinux.com> <20060126033613.GG11138@miraclelinux.com> <661de9470601252312m1f9c9256peb79451e49fc8662@mail.gmail.com> <20060127045522.GA7587@miraclelinux.com> <661de9470601262140x4e870cd5me9ba0f8e9d52f421@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <661de9470601262140x4e870cd5me9ba0f8e9d52f421@mail.gmail.com> User-Agent: Mutt/1.5.9i From: mita@miraclelinux.com (Akinobu Mita) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1434 Lines: 36 On Fri, Jan 27, 2006 at 11:10:29AM +0530, Balbir Singh wrote: > On 1/27/06, Akinobu Mita wrote: > > On Thu, Jan 26, 2006 at 12:42:09PM +0530, Balbir Singh wrote: > > > > > > +static inline unsigned int hweight32(unsigned int w) > > > > +{ > > > > + unsigned int res = (w & 0x55555555) + ((w >> 1) & 0x55555555); > > > > + res = (res & 0x33333333) + ((res >> 2) & 0x33333333); > > > > + res = (res & 0x0F0F0F0F) + ((res >> 4) & 0x0F0F0F0F); > > > > + res = (res & 0x00FF00FF) + ((res >> 8) & 0x00FF00FF); > > > > + return (res & 0x0000FFFF) + ((res >> 16) & 0x0000FFFF); > > > > +} > > > > + > > > > > > This can be replaced with > > > > > > register int res=w; > > > res=res-((res>>1)&0x55555555); > > > res=(res&0x33333333)+((res>>2)&0x33333333); > > > res=(res+(res>>4))&0x0f0f0f0f; > > > res=res+(res>>8); > > > return (res+(res>>16)) & 0xff; > > > > Probably you are right. > > Unfortunately, it is difficult for me to prove that sane equivalence. > > > > Well, a proof is not difficult. This is a well tested proven piece of > code published by Don Knuth. If you need a proof, I can provide one. Thanks, I want. - 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/