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Bug #47208 Converting Float/Double to Integer bug.
Submitted: 2009-01-24 13:44 UTC Modified: 2009-01-24 16:23 UTC
From: superdude at hotmail dot com Assigned:
Status: Not a bug Package: Math related
PHP Version: 5.2.8 OS: win32/64 possibly others.
Private report: No CVE-ID: None
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 [2009-01-24 13:44 UTC] superdude at hotmail dot com
Description:
------------
When multiplying a float/double that the has value of 1.003, converting it to a integer, will always return the expected value, minus 1.

Reproduce code:
---------------
<?php
$x = 1.003;
echo (int)($x*1000)."<br>\n";
echo (int)($x*10000)."<br>\n";
echo (int)($x*100000)."<br>\n";
?>

Expected result:
----------------
1003
10030
100300

Actual result:
--------------
1002
10029
100299

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 [2009-01-24 16:23 UTC] mattwil@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.

1.003 is stored as slightly less than that (close as possible), which can be seen when you show enough digits:

printf('%.20f', 1.003);

Gives 1.00299999999999989164 for me...
 
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