Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S271364AbTHMD5y (ORCPT ); Tue, 12 Aug 2003 23:57:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S271365AbTHMD5y (ORCPT ); Tue, 12 Aug 2003 23:57:54 -0400 Received: from dyn-ctb-210-9-243-246.webone.com.au ([210.9.243.246]:52746 "EHLO chimp.local.net") by vger.kernel.org with ESMTP id S271364AbTHMD5w (ORCPT ); Tue, 12 Aug 2003 23:57:52 -0400 Message-ID: <3F39B702.7000406@cyberone.com.au> Date: Wed, 13 Aug 2003 13:56:50 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.3.1) Gecko/20030618 Debian/1.3.1-3 X-Accept-Language: en MIME-Version: 1.0 To: Albert Cahalan CC: andersen@codepoet.org, linux-kernel mailing list , bernd@firmix.at, Anthony.Truong@mascorp.com, alan@lxorguk.ukuu.org.uk, schwab@suse.de, ysato@users.sourceforge.jp, willy@w.ods.org, Valdis.Kletnieks@vt.edu, william.gallafent@virgin.net Subject: Re: generic strncpy - off-by-one error References: <1060741101.948.245.camel@cube> <20030813024752.GA20369@codepoet.org> <1060745910.948.268.camel@cube> In-Reply-To: <1060745910.948.268.camel@cube> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1718 Lines: 67 Albert Cahalan wrote: >On Tue, 2003-08-12 at 22:47, Erik Andersen wrote: > >>On Tue Aug 12, 2003 at 10:18:21PM -0400, Albert Cahalan wrote: >> >>>You're all wrong. This is some kind of programming >>>test for sure! >>> >>>Let us imagine that glibc has a correct version. >>>By exhaustive testing, I found a version that works. >>>Here it is, along with the test code: >>> >>>////////////////////////////////////////////////////// >>>#define _GNU_SOURCE >>>#include >>>#include >>>#include >>> >>>// first correct implementation! >>>char * strncpy_good(char *dest, const char *src, size_t count){ >>> char *tmp = dest; >>> memset(dest,'\0',count); >>> while (count-- && (*tmp++ = *src++)) >>> ; >>> return dest; >>>} >>> >>char *strncpy(char * s1, const char * s2, size_t n) >>{ >> register char *s = s1; >> while (n) { >> if ((*s = *s2) != 0) s2++; >> ++s; >> --n; >> } >> return s1; >>} >> > >That's excellent. On ppc I count 12 instructions, >4 of which would go away for typical usage if inlined. >Annoyingly, gcc doesn't get the same assembly from my >attempt at that general idea: > >char * strncpy_5(char *dest, const char *src, size_t count){ > char *tmp = dest; > while (count--){ > if(( *tmp++ = *src )) src++; > } > return dest; >} > >I suppose that gcc could use a bug report. > Its has different semantics though. Well taken as a whole they are the same. When your loop finishes, count will be -1. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/