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Bug #54414 Floating-Point Arithmetic Bug
Submitted: 2011-03-28 20:57 UTC Modified: 2011-03-28 21:32 UTC
From: ejsexton82 at gmail dot com Assigned:
Status: Not a bug Package: Math related
PHP Version: 5.3.6 OS: Windows Server 2003
Private report: No CVE-ID: None
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 [2011-03-28 20:57 UTC] ejsexton82 at gmail dot com
Description:
------------
The following calculation yields an unexpected result.

Test script:
---------------
$test = 625.0 - 661.7 + 37.0;
var_dump($test);

Expected result:
----------------
0.3

Actual result:
--------------
0.29999999999995

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 [2011-03-28 21:32 UTC] dtajchreber@php.net
-Status: Open +Status: Bogus
 [2011-03-28 21:32 UTC] dtajchreber@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.


 
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