Re: [Full-disclosure] 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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