Description:
------------
I have made a simple hashing function and it returns bad value!

Reproduce code:
---------------
function hash ($MAIL, $PASS)
{
	//$amail = str_split($MAIL);
	//$apass = str_split($PASS);
	$mdl=strlen($MAIL);
	for($z=0;$z<$mdl;$z++)
	{
		$amail[$z] = $MAIL{$z};
	}
	$pdl=strlen($PASS);
	for($z=0;$z<$pdl;$z++)
	{
		$apass[$z] = $PASS{$z};
	}
	$tab = array_merge($apass, $amail);
	$b = -1;
	$i=0;
	while( ($c = ord($tab[$i++])) != '' )
	{
		$a = ($c ^ $b) + ($c << 8);
		$b = ($a >> 24) | ($a << 8);
	}
	return ($b < 0 ? -$b : $b);
}
$m = "test@mail.com";
$p = "testpass";

$fun = hash($m, $p);

Expected result:
----------------
on 3rd or 4th value of calculating hash everything go down ... there is very small number eg. -16 or sommething but there should be a huge one... like -4168570667... dudes what to do ??


Actual result:
--------------
best regards :)