Bug #64307 [Com]: Floating point error

From: Date: Wed, 27 Feb 2013 09:46:45 +0000
Subject: Bug #64307 [Com]: Floating point error
References: 1  Groups: php.bugs 
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Edit report at https://bugs.php.net/bug.php?id=64307&edit=1

 ID:                 64307
 Comment by:         sokkis at gmail dot com
 Reported by:        sokkis at gmail dot com
 Summary:            Floating point error
 Status:             Not a bug
 Type:               Bug
 Package:            Variables related
 Operating System:   Gentoo linux
 PHP Version:        5.4.12
 Block user comment: N
 Private report:     N

 New Comment:

"Floating point values have a limited precision"

It's ok, but why not:
244350,00000000... - 244350 = 2.9103830456734E-11
the output?

So, if floating point variable has limited precision, it has it if echod, and has 
if make subractions, or any other.


Previous Comments:
------------------------------------------------------------------------
[2013-02-27 09:42:45] pajoye@php.net

Floating point values have a limited precision. Hence a value might 
not have the same string representation after any processing. That also
includes writing a floating point value in your script and directly 
printing it without any mathematical operations.

If you would like to know more about "floats" and what IEEE
754 is, read this:
http://www.floating-point-gui.de/

Thank you for your interest in PHP.



------------------------------------------------------------------------
[2013-02-27 09:31:27] sokkis at gmail dot com

Description:
------------
Floating point rounded when print, but won't on subtraction.

Test script:
---------------
<?php
    $n1 = 905000;
    $n2 = 0.27;
    $ertek =$n1*$n2;
    $egesz = round( $ertek );
    $eredmeny = $ertek-$egesz;
    echo "$ertek - $egesz = $eredmeny\n";

    $n1 = 905000;
    $n2 = 0.27;
    $ertek =$n1*$n2;
    $egesz = (int) $ertek;
    $eredmeny = $ertek-$egesz;
    echo "$ertek - $egesz = $eredmeny";


Expected result:
----------------
244350 - 244350 = 0
244350 - 244350 = 0

Actual result:
--------------
244350 - 244350 = 2.9103830456734E-11
244350 - 244350 = 2.9103830456734E-11


------------------------------------------------------------------------



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