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

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Message-ID: <20070928194402.GF22656@darkover.org>
Date: Fri, 28 Sep 2007 16:44:02 -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); }

Isn't this the same issue pointed out by Brian Kim (double to float 
conversion) ?

Look the results I get for the following code:

volatile double a = 5.2;
volatile double b = 0.1;
main() {
        printf("%.16lf\n",a);
        printf("%.16lf\n",b);
        printf("%.16lf\n",(volatile double) 5.1);
        printf("%.16lf\n",(volatile double)((float) 5.1));
        printf("%.16lf\n",a-b);
}


Results:
5.2000000000000002
0.1000000000000000
5.0999999999999996
5.0999999046325684	<------------
5.1000000000000005


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

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