From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932634AbWAFXVN (ORCPT ); Fri, 6 Jan 2006 18:21:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932645AbWAFXVN (ORCPT ); Fri, 6 Jan 2006 18:21:13 -0500 Received: from omta04ps.mx.bigpond.com ([144.140.83.156]:6325 "EHLO omta04ps.mx.bigpond.com") by vger.kernel.org with ESMTP id S932634AbWAFXVN (ORCPT ); Fri, 6 Jan 2006 18:21:13 -0500 Message-ID: <43BEFB62.5050407@bigpond.net.au> Date: Sat, 07 Jan 2006 10:21:06 +1100 From: Peter Williams User-Agent: Mozilla Thunderbird 1.0.7-1.1.fc4 (X11/20050929) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Eric Dumazet CC: Linux Kernel Mailing List Subject: Re: [PATCH] lib: Fix bug in int_sqrt() for 64 bit longs References: <43BDFC8B.9020805@bigpond.net.au> <43BE1168.1090706@cosmosbay.com> In-Reply-To: <43BE1168.1090706@cosmosbay.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Authentication-Info: Submitted using SMTP AUTH PLAIN at omta04ps.mx.bigpond.com from [147.10.133.38] using ID pwil3058@bigpond.net.au at Fri, 6 Jan 2006 23:21:06 +0000 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Eric Dumazet wrote: > Peter Williams a écrit : > >> The implementation of int_sqrt() assumes that longs have 32 bits. On >> systems that have 64 bit longs this will result in gross errors when >> the argument to the function is greater than 2^32 - 1 on such systems. >> I doubt whether any such use is currently made of int_sqrt() but the >> attached patch fixes the problem anyway. >> >> Signed-off-by: Peter Williams >> >> >> ------------------------------------------------------------------------ >> >> Index: GIT-warnings/lib/int_sqrt.c >> =================================================================== >> --- GIT-warnings.orig/lib/int_sqrt.c 2005-10-25 13:55:22.000000000 >> +1000 >> +++ GIT-warnings/lib/int_sqrt.c 2006-01-06 14:29:19.000000000 +1100 >> @@ -15,7 +15,7 @@ unsigned long int_sqrt(unsigned long x) >> op = x; >> res = 0; >> >> - one = 1 << 30; >> + one = 1 << (BITS_PER_LONG - 2); >> while (one > op) >> one >>= 2; >> > > > Are you sure it works ? > > I would have writen : > > one = 1L << (BITS_PER_LONG - 2); I think you're right as just using 1 would make the expression an integer variable and the compiler would complain about shifting too far unless integers were the same size as longs. (I don't have a 64 bit system to confirm that on which is why it snuck by me. :-() Thanks Peter -- Peter Williams pwil3058@bigpond.net.au "Learning, n. The kind of ignorance distinguishing the studious." -- Ambrose Bierce