From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932113AbWAYUDK (ORCPT ); Wed, 25 Jan 2006 15:03:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751190AbWAYUDK (ORCPT ); Wed, 25 Jan 2006 15:03:10 -0500 Received: from caramon.arm.linux.org.uk ([212.18.232.186]:26639 "EHLO caramon.arm.linux.org.uk") by vger.kernel.org with ESMTP id S1751177AbWAYUDI (ORCPT ); Wed, 25 Jan 2006 15:03:08 -0500 Date: Wed, 25 Jan 2006 20:02:50 +0000 From: Russell King To: Akinobu Mita Cc: linux-kernel@vger.kernel.org, Richard Henderson , Ivan Kokshaysky , Ian Molton , dev-etrax@axis.com, David Howells , Yoshinori Sato , Linus Torvalds , linux-ia64@vger.kernel.org, Hirokazu Takata , linux-m68k@vger.kernel.org, Greg Ungerer , linux-mips@linux-mips.org, parisc-linux@parisc-linux.org, linuxppc-dev@ozlabs.org, linux390@de.ibm.com, linuxsh-dev@lists.sourceforge.net, linuxsh-shmedia-dev@lists.sourceforge.net, sparclinux@vger.kernel.org, ultralinux@vger.kernel.org, Miles Bader , Andi Kleen , Chris Zankel Subject: Re: [PATCH 3/6] C-language equivalents of include/asm-*/bitops.h Message-ID: <20060125200250.GA26443@flint.arm.linux.org.uk> Mail-Followup-To: Akinobu Mita , linux-kernel@vger.kernel.org, Richard Henderson , Ivan Kokshaysky , Ian Molton , dev-etrax@axis.com, David Howells , Yoshinori Sato , Linus Torvalds , linux-ia64@vger.kernel.org, Hirokazu Takata , linux-m68k@lists.linux-m68k.org, Greg Ungerer , linux-mips@linux-mips.org, parisc-linux@parisc-linux.org, linuxppc-dev@ozlabs.org, linux390@de.ibm.com, linuxsh-dev@lists.sourceforge.net, linuxsh-shmedia-dev@lists.sourceforge.net, sparclinux@vger.kernel.org, ultralinux@vger.kernel.org, Miles Bader , Andi Kleen , Chris Zankel References: <20060125112625.GA18584@miraclelinux.com> <20060125113206.GD18584@miraclelinux.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060125113206.GD18584@miraclelinux.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 25, 2006 at 08:32:06PM +0900, Akinobu Mita wrote: > +#ifndef HAVE_ARCH___FFS_BITOPS > + > +/** > + * __ffs - find first bit in word. > + * @word: The word to search > + * > + * Returns 0..BITS_PER_LONG-1 > + * Undefined if no bit exists, so code should check against 0 first. > + */ > +static inline unsigned long __ffs(unsigned long word) > { > - int mask; > + int b = 0, s; > > - addr += nr >> 5; > - mask = 1 << (nr & 0x1f); > - return ((mask & *addr) != 0); > +#if BITS_PER_LONG == 32 > + s = 16; if (word << 16 != 0) s = 0; b += s; word >>= s; > + s = 8; if (word << 24 != 0) s = 0; b += s; word >>= s; > + s = 4; if (word << 28 != 0) s = 0; b += s; word >>= s; > + s = 2; if (word << 30 != 0) s = 0; b += s; word >>= s; > + s = 1; if (word << 31 != 0) s = 0; b += s; > + > + return b; > +#elif BITS_PER_LONG == 64 > + s = 32; if (word << 32 != 0) s = 0; b += s; word >>= s; > + s = 16; if (word << 48 != 0) s = 0; b += s; word >>= s; > + s = 8; if (word << 56 != 0) s = 0; b += s; word >>= s; > + s = 4; if (word << 60 != 0) s = 0; b += s; word >>= s; > + s = 2; if (word << 62 != 0) s = 0; b += s; word >>= s; > + s = 1; if (word << 63 != 0) s = 0; b += s; > + > + return b; > +#else > +#error BITS_PER_LONG not defined > +#endif This code generates more expensive shifts than our (ARMs) existing C version. This is a backward step. Basically, shifts which depend on a variable are more expensive than constant-based shifts. I've not really looked at the rest because I haven't figured out which bits will be used on ARM and which won't - which I think is another problem with this patch set. I'll look again later tonight. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: 2.6 Serial core