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Bug #44311 Bug in arithmetic operation: 173.42-173.42=2.8421709430404E-014
Submitted: 2008-03-02 13:25 UTC Modified: 2008-03-02 15:04 UTC
From: sawas at poczta dot onet dot pl Assigned:
Status: Not a bug Package: Math related
PHP Version: 4.4.8 OS: WinXP, Debian
Private report: No CVE-ID: None
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From: sawas at poczta dot onet dot pl
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 [2008-03-02 13:25 UTC] sawas at poczta dot onet dot pl 
Description:
------------
I found a bug in arithmetic operation.
Simple subtraction of amounts gives inaccurate result.

Reproduce code:
---------------
$a = 160.00 + 5.90 + 7.52;
$b = 173.42;
print $a-$b;

Expected result:
----------------
0

Actual result:
--------------
2.8421709430404E-014

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 [2008-03-02 15:04 UTC] scottmac@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://docs.sun.com/source/806-3568/ncg_goldberg.html
 
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