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From: loren@ural.Eng.Sun.COM
Newsgroups: comp.lang.perl
Subject: Re: Addition of floating point problem
Message-ID: <13012@exodus.Eng.Sun.COM>
Date: 8 May 91 21:22:40 GMT
References: <1991May07.174519.13307@dircon.co.uk>
Sender: news@exodus.Eng.Sun.COM
Organization: Sun Microsystems, Mt. View, Ca.
Lines: 26

In article <1991May07.174519.13307@dircon.co.uk> uaa1006@dircon.co.uk
(Peter Miles) writes:
>
>Hi...I'm trying to write some maths scripts for perl and have 
>been have a major problem. This is best summed up by the following:
>
>$ perl -e 'print 0.5 + 0.2,"\n"'
>0.6999999999999996
>$
>
>What's going on? I'm running perl verion 4.0.1.1 patchlevel 3 on
>SCO UNIX 386 v 3.2.2. It's the version from comp.sources.misc.

This is exactly what the %g in printf is for.  Try the following:

    $ perl -e 'printf "%g\n", 0.5 + 0.2'
    0.7

The problem you have is because there is no *exact* representation
for .2 in most floating point systems.  The %g format specifier is
designed to take care of exactly this problem.

-----------------------------------------------------------------------------
Mr Loren L. Hart                        The Ada Ace Group, Inc
loren@cup.portal.com                    P.O. Box 36195
                                        San Jose, CA  95158