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content-class:	urn:content-classes:message
Subject:	RE: Strange behavior
Date:	Mon, 4 Mar 2002 16:26:23 +1100
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Message-ID:	<FC169E059D1A0442A04C40F86D9BA76008AB01@itdomain003.itdomain.net.au>
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Thread-Topic:	Strange behavior
Thread-Index:	AcHDOpnaMrDEMR1oRjyR6Ik1DXHEmgAAj/PA
From:	"Robert Collins" <robert DOT collins AT itdomain DOT com DOT au>
To:	"Chuck Allison" <cda AT freshsources DOT com>,
	"Richard R. Malloy" <rrmalloy AT attbi DOT com>,
	"Randall R Schulz" <rrschulz AT cris DOT com>
Cc:	"Ross Smith" <rosss AT pharos DOT co DOT nz>, <cygwin AT cygwin DOT com>
X-MIME-Autoconverted:	from quoted-printable to 8bit by delorie.com id g245RCd17420

Floating point comparisons should _always_ be done via a confidence
interval, not bitwise equality. As for determinism, I don't know what
the logic circuits look like, so can't and won't comment :}.

Rob



> -----Original Message-----
> From: Chuck Allison [mailto:cda AT freshsources DOT com] 
> Sent: Monday, March 04, 2002 4:08 PM
> To: Richard R. Malloy; Randall R Schulz
> Cc: Ross Smith; cygwin AT cygwin DOT com
> Subject: Re: Strange behavior
> 
> 
> That's the point. They're always redued, so in both cases, 
> the expression 2.0/3.0 is evaluated. How can that be 
> non-deterministic?
> 
> ----- Original Message -----
> From: "Richard R. Malloy" <rrmalloy AT attbi DOT com>
> To: "Randall R Schulz" <rrschulz AT cris DOT com>
> Cc: "Ross Smith" <rosss AT pharos DOT co DOT nz>; "'Chuck Allison'" 
> <cda AT freshsources DOT com>; <cygwin AT cygwin DOT com>
> Sent: Sunday, March 03, 2002 9:47 PM
> Subject: Re: Strange behavior
> 
> 
> > OK. I'm no IA32 expert can someone explain the following 
> results.  (Do 
> > the floating point registers use guard bits, randomly initialized 
> > perhaps?)
> >
> > bool operator==(const Rational& r1, const Rational& r2)
> > {
> >   double a=r1.toDouble(), b=r2.toDouble();
> >   cout << ?== a " << a << " " << ?== b " << b << endl;
> >   return a == b;
> >   //  return r1.toDouble() == r2.toDouble();
> >   /*  return ( r1.numerator == r2.numerator && r1.denominator == 
> > r2.denominator ); */ }

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