php.net |  support |  documentation |  report a bug |  advanced search |  search howto |  statistics |  random bug |  login

go to bug id or search bugs for

Bug #31569 Incorrect Values Returned
Submitted: 2005-01-16 12:59 UTC Modified: 2005-02-01 19:02 UTC
From: php at milonic dot com Assigned:
Status: Not a bug Package: Math related
PHP Version: 4CVS-2005-01-16 OS: Fedora/Linux 9
Private report: No CVE-ID: None
View Developer Edit
Welcome back! If you're the original bug submitter, here's where you can edit the bug or add additional notes.
If you forgot your password, you can retrieve your password here.
Password:
Status:
Package:
Bug Type:
Summary:
From: php at milonic dot com
New email:
PHP Version: OS:

 

 [2005-01-16 12:59 UTC] php at milonic dot com 
Description:
------------
Values returned using the following code produce different results (incorrect) in PHP-4.3.10 and PHP-4.3.9 on Fedora Core 3. 

When the same code is executed on a Linux 9 or FreeBSD5.3 machine the values are correct.

Could be a Fedora problem but thought you'd like to take a look.

Reproduce code:
---------------
<?

function fillZeros($a, $b){
	$z = hexdec(80000000);
	if ($z & $a){
		$a = ($a>>1);
		$a &= (~$z);
		$a |= 0x40000000;
		$a = ($a>>($b-1));
	}
	else{
		$a = ($a>>$b);
	}
	return $a;
}



function mixture($a,$b,$c) 
{
	$a -= $b; $a -= $c; $a ^= (fillZeros($c,13));
	$b -= $c; $b -= $a; $b ^= ($a<<8);
	$c -= $a; $c -= $b; $c ^= (fillZeros($b,13));
	$a -= $b; $a -= $c; $a ^= (fillZeros($c,12));
	$b -= $c; $b -= $a; $b ^= ($a<<16);
	$c -= $a; $c -= $b; $c ^= (fillZeros($b,5));
	$a -= $b; $a -= $c; $a ^= (fillZeros($c,3)); 
	$b -= $c; $b -= $a; $b ^= ($a<<10);
	$c -= $a; $c -= $b; $c ^= (fillZeros($b,15));
	return array($a,$b,$c);
}


$test= mixture("11", "22", "33");
echo "$test[0], $test[1], $test[2]\n";

?>

Expected result:
----------------
Should be: 
251066875, -1654377486, -1500734959







Actual result:
--------------
But instead get:
251066875, 1541925888, -402039036

Only happens on Fedora, all other boxes are fine.

Patches

Pull Requests

History

AllCommentsChangesGit/SVN commitsRelated reports
 [2005-01-16 13:05 UTC] derick@php.net 
Please try using this CVS snapshot:

  http://snaps.php.net/php4-STABLE-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php4-win32-STABLE-latest.zip
 [2005-01-16 14:34 UTC] php at milonic dot com 
Sorry but it's still the same even with 4.3.11-DEV

My guess is that this could be a Fedora problem but would like to know either way.

It also seems unrelated to PHP version, happens on all of them both 4 and 5 - It all points to Fedora but just cannot think how.

I'll dig a little deeper and let you know if I find anything

Cheers
Andy
 [2005-01-16 14:45 UTC] php at milonic dot com 
Narrowed the problem down to this:

$b=251066875;
$a=-3111919630;
echo $b ^= ($a<<10);

     Fedora 3 echos: 251066875 (wrong)
All other OS's echo: 25768443 (correct)

Maybe it helps?

Cheers
Andy
 [2005-01-16 14:55 UTC] derick@php.net 
Did you compile from source? If so, what are the different GCC versions on all machines?
 [2005-01-16 15:19 UTC] php at milonic dot com 
Yes from source:
gcc version 3.4.2 20041017 (Red Hat 3.4.2-6.fc3)

one that I know works fine is:
gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)

Basically, all machines other than 'Fedora Core 3' are working fine. It's something in FC3 that is wrong, I just can't pinpoint it. 

It's a standard server install by the way, nothing special. Hardware also seems to be unrelated to the problem, tried it on 2 different FC3 servers and get the same result.

Cheers
Andy
 [2005-01-16 15:38 UTC] php at milonic dot com 
UPDATE:

Just to confirm that it's also the same with RPM-4.3.9 - so no matter if it's compiled from source or package.

Also (was a long shot) changing precision in php.ini makes no difference either

Cheers
Andy
 [2005-01-16 17:05 UTC] php at milonic dot com 
New test case at:
http://www.milonic.com/bugreports/php_fc3.php

Can also confirm that JavaScript will return the same values that older Redhat returns. This is getting weirder by the minute.

Cheers
Andy
 [2005-01-18 13:09 UTC] jorton@php.net 
$a=-3111919630;
echo $b ^= ($a<<10);

1. -3111919630 cannot be represented in a 32-bit long, so it's stored in a double
2. "$a << 10" is executed using (long) integer arithmetic, so $a is converted to a long here
3. the Zend macro which converts double to long used to be miscompiled by GCC, but this was fixed in the FC3 gcc.
 [2005-02-01 19:02 UTC] sniper@php.net 
Not PHP bug but FC3 gcc bug.
 
PHP Copyright © 2001-2024 The PHP Group
All rights reserved. 		Last updated: Sun Dec 22 01:01:30 2024 UTC