From: Albert Cahalan <albert@users.sf.net>
To: andersen@codepoet.org
Cc: Albert Cahalan <albert@users.sourceforge.net>,
linux-kernel mailing list <linux-kernel@vger.kernel.org>,
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
Date: 12 Aug 2003 23:38:31 -0400 [thread overview]
Message-ID: <1060745910.948.268.camel@cube> (raw)
In-Reply-To: <20030813024752.GA20369@codepoet.org>
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 <string.h>
> > #include <stdlib.h>
> > #include <stdio.h>
> >
> > // 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.
next prev parent reply other threads:[~2003-08-13 3:49 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-08-13 2:18 generic strncpy - off-by-one error Albert Cahalan
2003-08-13 2:47 ` Erik Andersen
2003-08-13 3:38 ` Albert Cahalan [this message]
2003-08-13 3:56 ` Nick Piggin
2003-08-13 5:18 ` Willy Tarreau
2003-08-13 19:03 ` Timothy Miller
-- strict thread matches above, loose matches on Subject: below --
2003-08-20 7:43 Peter Kjellerstedt
2003-08-16 21:10 Peter Kjellerstedt
2003-08-18 18:41 ` Timothy Miller
2003-08-16 20:08 Peter Kjellerstedt
2003-08-16 9:19 Peter Kjellerstedt
2003-08-16 10:04 ` Daniel Forrest
2003-08-18 16:40 ` Timothy Miller
2003-08-16 8:15 Peter Kjellerstedt
2003-08-16 8:41 ` Daniel Forrest
2003-08-18 16:17 ` Timothy Miller
2003-08-18 16:06 ` Timothy Miller
2003-08-15 9:54 Peter Kjellerstedt
2003-08-15 17:52 ` Timothy Miller
2003-08-15 9:53 Peter Kjellerstedt
2003-08-15 17:47 ` Timothy Miller
2003-08-14 9:34 Peter Kjellerstedt
2003-08-14 19:45 ` Willy Tarreau
2003-08-14 20:24 ` Timothy Miller
2003-08-13 3:09 Anthony Truong
2003-08-12 14:07 Yoshinori Sato
2003-08-12 14:39 ` Willy Tarreau
2003-08-12 14:50 ` Yoshinori Sato
2003-08-12 15:03 ` Valdis.Kletnieks
2003-08-12 15:54 ` William Gallafent
2003-08-12 16:19 ` Valdis.Kletnieks
2003-08-12 16:09 ` Andreas Schwab
2003-08-12 1:56 Anthony Truong
2003-08-12 17:14 ` Alan Cox
2003-08-12 21:53 ` Bernd Petrovitsch
2003-08-12 1:28 Anthony Truong
2003-08-12 16:24 ` Bernd Petrovitsch
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