Php sum from two string that over 65535 int

gistfile1.txt

<?php
$str  = '11000000000000000000000 33';
//echo 11000000000000000000000+33 will produce 1.1E+22983411000000000000000000030

//but with this code you will get  11000000000000000000033
$e    = explode(" ", $str);
$num1 = $e[0];
$num2 = $e[1];
//100
// 10
// or
//10
//100
$lenNum1 = strlen($num1);
$lenNum2 = strlen($num2);
if($lenNum1 < $lenNum2) {
	$tmp = $num2;
	$num2 = $num1;
	$num1 = $tmp;
}

$cur = 0;
$offset = strlen($num1) - strlen($num2);
$res  = '';
$prev = 0;
$num2 = str_split($num2);

foreach (str_split($num1) as $k => $sym) {
	$intNum  = (int) $sym;
	$intNum2 = 0;
	if ($cur >= $offset && isset($num2[$k-$offset])) {
		$intNum2 = (int) $num2[$k-$offset];
	}

	$s = $intNum + $intNum2;
	if ($s >= 10) {
		$res = (int) $prev + 1;
		$s   = $s - 10;
	}

	$res .= $s;
	$prev = $res;
	$cur++;
}

echo $res . "\n";