From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Henderson Date: Thu, 26 Jan 2006 00:06:18 +0000 Subject: Re: [PATCH 3/6] C-language equivalents of include/asm-*/bitops.h Message-Id: <20060126000618.GA5592@twiddle.net> List-Id: References: <20060125112625.GA18584@miraclelinux.com> <20060125113206.GD18584@miraclelinux.com> <20060125200250.GA26443@flint.arm.linux.org.uk> In-Reply-To: <20060125200250.GA26443@flint.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Akinobu Mita , linux-kernel@vger.kernel.org, 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 On Wed, Jan 25, 2006 at 08:02:50PM +0000, Russell King wrote: > > + 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; ... > Basically, shifts which depend on a variable are more expensive than > constant-based shifts. Actually, they're all constant shifts. Just written stupidly. r~