Large Powers Corrupt

jrpruitt

Can someone please offer a work-a-round for the following script.

Adding $x1 and $x2 together works fine, but when I take the
result (in $y1) to the power of $x3, it fails on some Linux platforms,
but not others. Makes no difference if using PHP 4 or PHP 5.

I've tested this on seven different servers.
On any that are running RedHat 9 or FreeBSD, the
script works correctly. On any running CentOS (32 bit)
or RedHat Enterprise, the script comes up with the
wrong answer.

<?php
$x1=-1639260211;
$x2=-1558980842;
$x3=3888969200;

$y1 = $x1+$x2;
$y2 = ($y1) ^ ($x3);

echo "y1: ".$y1."\n";
echo "y2: ".$y2."\n";
?>

FreeBSD:
y1: -3198241053
y2: -1500364013 <--- The correct answer

CentOS:
y1: -3198241053
y2: 1741485552 <--- The Wrong answer

laserlight

$y1 ^ $x3 computes the bitwise XOR of $y1 and $x3, not $y1 to the power of $x3.

In any case, for such large numbers you would need a bignum library extension like the GMP functions.

jrpruitt

Thanks, laserlight!!!!

The following script works great.

<?php
$x1=(-1639260211);
$x2=(-1558980842);
$x3=3888969200;

$y1 = $x1+$x2;
$s1 =sprintf("%12.0f",$y1);
$s2 =sprintf("%12.0f",$x3);
$g1 = gmp_init($s1,10);
$g2 = gmp_init($s2,10);

$y2 = gmp_xor(($g1),($g2));

echo "y1: ".$y1."\n";
echo "y2: ".gmp_strval($y2)."\n";