From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julia Lawall Subject: Re: [PATCH 0/10] use safer test on the result of find_first_zero_bit Date: Wed, 4 Jun 2014 15:12:23 +0200 (CEST) Message-ID: References: <1401872880-23685-1-git-send-email-Julia.Lawall@lip6.fr> <063D6719AE5E284EB5DD2968C1650D6D1725705F@AcuExch.aculab.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: Julia Lawall , David Laight , linux-rdma , "kernel-janitors@vger.kernel.org" , Linux Fbdev development list , Linux-sh list , "linux-kernel@vger.kernel.org" , "ath10k@lists.infradead.org" , linux-wireless , "netdev@vger.kernel.org" , driverdevel , "iss_storagedev@hp.com" , scsi , linux-s390 , "adi-buildroot-devel@lists.sourceforge.net" , Arnd Bergmann , sebott@linux.vnet.ibm.com To: Geert Uytterhoeven Return-path: In-Reply-To: Sender: kernel-janitors-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, 4 Jun 2014, Geert Uytterhoeven wrote: > Hi Julia, > > On Wed, Jun 4, 2014 at 1:00 PM, Julia Lawall wrote: > > OK, thanks. I was only looking at the C code. > > > > But the C code contains a loop that is followed by: > > > > if (!size) > > return result; > > tmp = *p; > > > > found_first: > > tmp |= ~0UL << size; > > if (tmp == ~0UL) /* Are any bits zero? */ > > return result + size; /* Nope. */ > > > > In the first return, it would seem that result == size. Could the second > > one be changed to just return size? It should not hurt performance. > > "size" may have been changed between function entry and this line. > So you have to store it in a temporary. Sorry, after reflection it seems that indeed size + result is always the original size, so it is actually all of the code that uses >= that is doing something unnecessary. == for the failure test is fine. julia