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From: Jakub Jelinek <jakub@redhat.com>
To: Ulrich Drepper <drepper@redhat.com>
Cc: Wolfram Gloger <wmglo@dent.med.uni-muenchen.de>,
	libc-hacker@sources.redhat.com
Subject: Re: [PATCH] xdr_array and calloc security fix
Date: Fri, 02 Aug 2002 02:56:00 -0000	[thread overview]
Message-ID: <20020802115506.C20867@sunsite.ms.mff.cuni.cz> (raw)
In-Reply-To: <3D4A55F0.5020007@redhat.com>; from drepper@redhat.com on Fri, Aug 02, 2002 at 02:50:40AM -0700

On Fri, Aug 02, 2002 at 02:50:40AM -0700, Ulrich Drepper wrote:
> Ulrich Drepper wrote:
> 
> > It should be possible to have something like
> > 
> >   ((a | b) > (a * b))
> > 
> > for unsigned values.  I'm not 100% sure, though.
> 
> I mean, this is an approximation which lets us avoid the division in 
> many (most?) cases.

Many. a=1 b=2 -> is this overflow?
a=0x6000000 b=64 -> this would signal no overflow, while in fact
it overflowed. Etc.
I think the only way is to put the multiply + check for overflow into some
macro and optimize it per-architecture...

	Jakub

  reply	other threads:[~2002-08-02  9:56 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2002-08-01 15:46 Jakub Jelinek
2002-08-02  0:20 ` Ulrich Drepper
2002-08-02  2:29 ` Wolfram Gloger
2002-08-02  2:43   ` Ulrich Drepper
2002-08-02  2:50     ` Ulrich Drepper
2002-08-02  2:56       ` Jakub Jelinek [this message]
2002-08-02  4:07         ` Andreas Schwab
2002-08-02  4:46           ` Jakub Jelinek
2002-08-02  4:57             ` Wolfram Gloger
2002-08-02  5:05               ` Jakub Jelinek
2002-08-02  5:13                 ` Wolfram Gloger
2002-08-03  5:03                   ` [PATCH] optimize calloc Jakub Jelinek
2002-08-03 12:02                     ` Ulrich Drepper

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