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Bug #42812 integer value returned by php incorrect
Submitted: 2007-10-01 10:33 UTC Modified: 2007-10-01 10:38 UTC
From: laurent at polenord dot com Assigned:
Status: Not a bug Package: Scripting Engine problem
PHP Version: 5.2.4 OS: linux
Private report: No CVE-ID: None
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From: laurent at polenord dot com
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 [2007-10-01 10:33 UTC] laurent at polenord dot com
Description:
------------
infact the problem occurs on PHP 5.2.3

I want to simply return a float multiplied by a million, and force it to an integer value to avoid php returns int in weird format (2.9E+06 for example), and it doesn't return the correct value.

This is very strange as it seems to occurs only on the '2.09' value : it's ok with 1.09 and 3.09, 2.19, 2.091 and 2.089, etc...


Reproduce code:
---------------
$cpc = '2.09';

echo $cpc * 1000000; // returns correct value : 2090000
echo "<br/>";
echo (int)($cpc * 1000000); // returns 2089999 !!
echo "<br/>";
echo (int)($cpc * 1000 * 1000); // return correct value.

Expected result:
----------------
2090000
2090000
2090000

Actual result:
--------------
2090000
2089999
2090000

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 [2007-10-01 10:38 UTC] 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://docs.sun.com/source/806-3568/ncg_goldberg.html
 
Thank you for your interest in PHP.

NB: remove the (int) cast to see what actually happens.
 
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