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Bug #67257 Edge case error when casting to integer
Submitted: 2014-05-12 11:24 UTC Modified: 2014-05-12 16:23 UTC
From: cc at altruja dot de Assigned:
Status: Not a bug Package: *General Issues
PHP Version: Irrelevant OS: Linux
Private report: No CVE-ID: None
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From: cc at altruja dot de
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 [2014-05-12 11:24 UTC] cc at altruja dot de 
Description:
------------
There seems to be an oddity in an edge case of casting float to integer after multiplying it with a multiple of 10. It only seems to occur with .4 after the decimal point, and only between 256.4 and 328.4. 

Test script:
---------------
<?php

var_dump((integer) (255.4 * 100));
var_dump((integer) (256.4 * 100));
var_dump((integer) (256.3 * 100));
var_dump((integer) (327.4 * 100));
var_dump((integer) (328.4 * 100));

Expected result:
----------------
int(25540)
int(25640)
int(25630)
int(32740)
int(32840)

Actual result:
--------------
int(25540)
int(25639)
int(25630)
int(32739)
int(32840)

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 [2014-05-12 16:23 UTC] requinix@php.net
-Status: Open +Status: Not a bug
 [2014-05-12 16:23 UTC] requinix@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.

256.4 is represented internally like 256.39999999999999998 and multiplying exposes that error.

Do a round(256.4 * 100, -1) to get your expected result.
 
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