Bug 212528

Summary: Math functions problem ( ($x<<$n) | ((pow(2, $n) - 1) & ($x>>(32-$n))) )
Product: Red Hat Enterprise Linux 4 Reporter: Need Real Name <vasek>
Component: phpAssignee: Joe Orton <jorton>
Status: CLOSED NOTABUG QA Contact: David Lawrence <dkl>
Severity: medium Docs Contact:
Priority: medium    
Version: 4.0   
Target Milestone: ---   
Target Release: ---   
Hardware: x86_64   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2006-12-11 11:54:05 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description Need Real Name 2006-10-27 08:48:48 UTC 
Description of problem:

I am usin a new RH EL 4 and have a problem with this function. The output is 
not corect and I tryed it also on some other systems and they also have this 
same bug. On my old server with RH 7.3 is answer corect. I think that is 
architecture independent, because do it also on i386 systems.
There is some informations about system :

affected system: 
Red Hat Enterprise Linux ES release 4 (Nahant Update 4)
Linux www.prolux.cz 2.6.9-42.0.3.ELsmp #1 SMP Mon Sep 25 17:24:31 EDT 2006 
x86_64 x86_64 x86_64 GNU/Linux
php-4.3.9-3.18


correct working system:
Red Hat Linux release 7.3 (Valhalla)
Linux prolux.speednet.cz 2.4.20-28.7 #1 Thu Dec 18 11:23:36 EST 2003 i686 
unknown
php-4.1.2-7.3.6


sorce code of php function :

<?
function L($x, $n) {
 return ( ($x<<$n) | ((pow(2, $n) - 1) & ($x>>(32-$n))) );
}

?>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=windows-1250">
<title></title>
</head>

<body>

<p><font size="4">Test of function:  return ( ($x<<$n) | ((pow(2, $n) - 1) & 
($x>>(32-$n))) );</font></p>
<table border="0" cellspacing="1" width="600">
  <tr>
    <td colspan="2">This is the correct answer:</td>
  </tr>
  <tr>
    <td><font color="#808080">INPUT: </font>-3086048340</td>
    <td><font color="#808080">OUTPUT:</font> 30700937</td>
  </tr>
  <tr>
    <td colspan="2"><hr noshade></td>
  </tr>
  <tr>
    <td colspan="2">Aswer of this function on this server:</td>
  </tr>
  <tr>
    <td><font color="#808080">input: </font>-3086048340</td>
    <td><font color="#808080">output:</font> <? echo L(-3086048340, 5) ?></td>
  </tr>
</table>
</body>
</html>


How reproducible:

Do it all times on affected server


Steps to Reproduce:

1. page on affected server with this source code : 
http://www2.prolux.cz/tmp/test.php
2. page on corect working server with same souce php code : 
http://router.prolux.cz/test.php

Thank you very much for answer, 


With the best regards

Vasek Valenta
Comment 1 Joe Orton 2006-12-11 11:54:05 UTC 
Thanks for the report.

The result of "-3086048340 << 5" will overflow signed 32-bit integer arithemetic
(as used internally by PHP) so the output of that function will not be
well-defined for that input.  If you need to reliably manipulate large integers
then the "gmp" extension can be used instead.