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Bug #68070 Wrong Answer to a fairly standard calculation
Submitted: 2014-09-22 10:10 UTC Modified: 2014-09-22 10:13 UTC
From: elliot at essentialsystems dot co dot uk Assigned:
Status: Not a bug Package: Math related
PHP Version: Irrelevant OS: Ubuntu
Private report: No CVE-ID: None
View Developer Edit
 [2014-09-22 10:10 UTC] elliot at essentialsystems dot co dot uk 
Description:
------------
The calculation in the test script should return 34, but yet is returning back 33.999999999998, which is very odd.

Test script:
---------------
<?php
//expecting 34
var_dump((40120.7 - 36346.0)-3740.7);
?>

Expected result:
----------------
Return back of the value of 34.

Actual result:
--------------
33.999999999998

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 [2014-09-22 10:13 UTC] nikic@php.net
-Status: Open +Status: Not a bug
 [2014-09-22 10:13 UTC] nikic@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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