X-Spam-Check-By: sourceware.org
Subject: Re: Precision of doubles and stdio
In-Reply-To: From Roberto Bagnara at "Mar 5, 2006 12:44:18 pm"
From: Jim Easton <jim AT cs DOT ualberta DOT ca>
To: Roberto Bagnara <bagnara AT cs DOT unipr DOT it>
Date: 	Mon, 6 Mar 2006 01:27:51 -0700 (MST)
CC: cygwin AT cygwin DOT com, Jim Easton <jim AT cs DOT ualberta DOT ca>
Message-Id: <S557523AbWCFI1v/20060306082754Z+38@sunkay.cs.ualberta.ca>
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Dear Mr. Bagnara,

Roberto Bagnara wrote: 
...
> does this on Linux/i686
> 
> $ a.out
> 70.9
> 70.900000000000005684341886080801486968994140625
> 
> and does the following under Cygwin on the same machine:
...
> $ ./a.exe
> 70.9
> 70.90000000000000568434188608080148696899414
> 
> Why?  Is there a way to reconcile the two behaviors?
> Notice that I know about the x87 and its vaguaries:
> nonetheless I wonder why such a scanf immediately
> followed by a printf shows a difference between
> Cygwin and Linux.

With all due respect, why would you want to?  With double you are
guaranteed only 16 or so digits - the rest is noise.  Frankly I am
amazed that it agrees as far as it does.

	Jim


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