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Re: [parisc-linux] Re: [PATCH 3/6] C-language equivalents of include/asm

To: Grant Grundler <grundler@parisc-linux.org>
Subject: Re: [parisc-linux] Re: [PATCH 3/6] C-language equivalents of include/asm-*/bitops.h
From: Nicolas Pitre <nico@cam.org>
Date: Thu, 26 Jan 2006 11:30:43 -0500 (EST)
Cc: Akinobu Mita <mita@miraclelinux.com>, lkml <linux-kernel@vger.kernel.org>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Ian Molton <spyro@f2s.com>, dev-etrax@axis.com, David Howells <dhowells@redhat.com>, Yoshinori Sato <ysato@users.sourceforge.jp>, Linus Torvalds <torvalds@osdl.org>, linux-ia64@vger.kernel.org, Hirokazu Takata <takata@linux-m32r.org>, linux-m68k@vger.kernel.org, Greg Ungerer <gerg@uclinux.org>, 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 <uclinux-v850@lsi.nec.co.jp>, Andi Kleen <ak@suse.de>, Chris Zankel <chris@zankel.net>
In-reply-to: <20060126161849.GA13632@colo.lackof.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20060125112625.GA18584@miraclelinux.com> <20060125113206.GD18584@miraclelinux.com> <20060125200250.GA26443@flint.arm.linux.org.uk> <20060126000618.GA5592@twiddle.net> <20060126085540.GA15377@flint.arm.linux.org.uk> <20060126161849.GA13632@colo.lackof.org>
Sender: linux-mips-bounce@linux-mips.org
On Thu, 26 Jan 2006, Grant Grundler wrote:

> On Thu, Jan 26, 2006 at 08:55:41AM +0000, Russell King wrote:
> > Unfortunately that's not correct.  You do not appear to have checked
> > the compiler output like I did - this code does _not_ generate
> > constant shifts.
> 
> Russell,
> By "written stupidly", I thought Richard meant they could have
> used constants instead of "s".  e.g.:
>       if (word << 16 == 0) { b += 16; word >>= 16); }
>       if (word << 24 == 0) { b +=  8; word >>=  8); }
>       if (word << 28 == 0) { b +=  4; word >>=  4); }
> 
> But I prefer what Edgar Toernig suggested.

It is just as bad on ARM since it requires large constants that cannot 
be expressed with immediate litteral values.  The constant shift 
approach is really the best on ARM.


Nicolas

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