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Date: Sun, 03 Mar 2002 18:20:39 -0800
To: Ross Smith <rosss AT pharos DOT co DOT nz>, "'Chuck Allison'" <cda AT freshsources DOT com>,
   cygwin AT cygwin DOT com
From: Randall R Schulz <rrschulz AT cris DOT com>
Subject: RE: Strange behavior
In-Reply-To: <79218202D4B9D4118A290002A508E13B79C373@PNZEXCHANGE>
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Ross,

To call that result "pure luck" denies the fact that digital computers, 
when properly functioning, are 100% deterministic.

Of course, it's not proper floating-point programming, but that doesn't 
mean "luck" is involved.

Randall Schulz
Mountain View, CA USA


At 18:04 2002-03-03, Ross Smith wrote:
> > From: Chuck Allison [mailto:cda AT freshsources DOT com]
> >
> > I have a simple Rational number class and have discovered
> > weird behavior
> > with Cygwin's g++. If you look at the very short main program in file
> > rtest2.cpp, you will see by the output that g++ get's the
> > wrong answer for
> >
> > r1 / r2 == Rational(2,3); // should be true
> >
> > even though it prints as 2/3! Borland and Microsoft get it
> > right. Any ideas?
> > All code atached.
>
>[relevant bit of code]
>
>inline bool operator==(const Rational& r1, const Rational& r2)
>{
>    return r1.toDouble() == r2.toDouble();
>}
>
>This is nothing to do with Cygwin, or g++ for that matter. You're 
>comparing floating point numbers. Of course it's not reliable! If other 
>compilers happened to give you an exact equality on that particular 
>combination of arguments, it was pure luck.


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