From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751090AbWBBOLJ (ORCPT ); Thu, 2 Feb 2006 09:11:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751082AbWBBOLI (ORCPT ); Thu, 2 Feb 2006 09:11:08 -0500 Received: from gra-lx1.iram.es ([150.214.224.41]:3022 "EHLO gra-lx1.iram.es") by vger.kernel.org with ESMTP id S1751078AbWBBOLF (ORCPT ); Thu, 2 Feb 2006 09:11:05 -0500 From: Gabriel Paubert Date: Thu, 2 Feb 2006 02:26:38 +0100 To: Akinobu Mita Cc: linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, linux-ia64@vger.kernel.org, Ian Molton , David Howells , linuxppc-dev@ozlabs.org, Greg Ungerer , sparclinux@vger.kernel.org, Miles Bader , Linus Torvalds , Yoshinori Sato , Hirokazu Takata , linuxsh-shmedia-dev@lists.sourceforge.net, linux-m68k@vger.kernel.org, Ivan Kokshaysky , Richard Henderson , Chris Zankel , dev-etrax@axis.com, ultralinux@vger.kernel.org, Andi Kleen , linuxsh-dev@lists.sourceforge.net, linux390@de.ibm.com, Russell King , parisc-linux@parisc-linux.org Subject: Re: [patch 14/44] generic hweight{64,32,16,8}() Message-ID: <20060202012637.GA25093@iram.es> References: <20060201090224.536581000@localhost.localdomain> <20060201090325.905071000@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060201090325.905071000@localhost.localdomain> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 01, 2006 at 06:02:38PM +0900, Akinobu Mita wrote: > > This patch introduces the C-language equivalents of the functions below: > > unsigned int hweight32(unsigned int w); > unsigned int hweight16(unsigned int w); > unsigned int hweight8(unsigned int w); > unsigned long hweight64(__u64 w); > > In include/asm-generic/bitops/hweight.h > > This code largely copied from: > include/linux/bitops.h > > Signed-off-by: Akinobu Mita > include/asm-generic/bitops/hweight.h | 54 +++++++++++++++++++++++++++++++++++ > 1 files changed, 54 insertions(+) > > Index: 2.6-git/include/asm-generic/bitops/hweight.h > =================================================================== > --- /dev/null > +++ 2.6-git/include/asm-generic/bitops/hweight.h > @@ -0,0 +1,54 @@ > +#ifndef _ASM_GENERIC_BITOPS_HWEIGHT_H_ > +#define _ASM_GENERIC_BITOPS_HWEIGHT_H_ > + > +#include > + > +/** > + * hweightN - returns the hamming weight of a N-bit word > + * @x: the word to weigh > + * > + * The Hamming Weight of a number is the total number of bits set in it. > + */ > + > +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); > +} The first step can be implemented slightly better: unsigned int res = w-((w>>1)&0x55555555); as I found once on the web[1]. Several of the following steps can also be simplified by omitting the masking when the result can't possibly cause a carry to propagate too far. This might also have a non negligible impact on code size. > + > +static inline unsigned int hweight16(unsigned int w) > +{ > + unsigned int res = (w & 0x5555) + ((w >> 1) & 0x5555); > + res = (res & 0x3333) + ((res >> 2) & 0x3333); > + res = (res & 0x0F0F) + ((res >> 4) & 0x0F0F); > + return (res & 0x00FF) + ((res >> 8) & 0x00FF); > +} > + > +static inline unsigned int hweight8(unsigned int w) > +{ > + unsigned int res = (w & 0x55) + ((w >> 1) & 0x55); > + res = (res & 0x33) + ((res >> 2) & 0x33); > + return (res & 0x0F) + ((res >> 4) & 0x0F); > +} > + > +static inline unsigned long hweight64(__u64 w) > +{ > +#if BITS_PER_LONG == 32 > + return hweight32((unsigned int)(w >> 32)) + hweight32((unsigned int)w); > +#elif BITS_PER_LONG == 64 > + u64 res; > + res = (w & 0x5555555555555555ul) + ((w >> 1) & 0x5555555555555555ul); > + res = (res & 0x3333333333333333ul) + ((res >> 2) & 0x3333333333333333ul); > + res = (res & 0x0F0F0F0F0F0F0F0Ful) + ((res >> 4) & 0x0F0F0F0F0F0F0F0Ful); > + res = (res & 0x00FF00FF00FF00FFul) + ((res >> 8) & 0x00FF00FF00FF00FFul); > + res = (res & 0x0000FFFF0000FFFFul) + ((res >> 16) & 0x0000FFFF0000FFFFul); > + return (res & 0x00000000FFFFFFFFul) + ((res >> 32) & 0x00000000FFFFFFFFul); > +#else > +#error BITS_PER_LONG not defined > +#endif > +} > + > +#endif /* _ASM_GENERIC_BITOPS_HWEIGHT_H_ */ > Regards, Gabriel [1] It might be better to write the first line unsigned res = w - ((w&0xaaaaaaaa)>>1); but I can never remember what the C standard guarantess about right shifts values (very little IIRC). I believe that it will work properly on all architectures that GCC supports, however, and that it will help on many.