full-disclosure - Re: Firefox 2.0.0.7 has a very serious calculation bug

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Date: Fri, 28 Sep 2007 16:29:18 -0300
From: Rodrigo Barbosa <rodrigob@...kover.org>
To: full-disclosure@...ts.grok.org.uk
Subject: Re: Firefox 2.0.0.7 has a very
	serious	calculation bug

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On Fri, Sep 28, 2007 at 09:09:02PM +0200, Michal Zalewski wrote:
> On Sat, 29 Sep 2007, Jimby Sharp wrote:
> 
> > I don't get the same from C-style double arithmetics. Could you provide
> > a sample code that you believe should show the same behavior?
> 
> If you don't, it's presumably because the subtraction is optimized out by
> the compiler, or because you printf() with an insufficient precision in
> format spec. The following should do the trick:
> 
> volatile double a = 5.2;
> volatile double b = 0.1;
> main() { printf("%.16lf\n",a-b); }

Confirmed here with:

gcc (GCC) 4.1.1 20070105 (Red Hat 4.1.1-52)

Actually quite interesting.

- -- 
Rodrigo Barbosa
"Quid quid Latine dictum sit, altum viditur"
"Be excellent to each other ..." - Bill & Ted (Wyld Stallyns)

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