PHP Damarau levenstein on Longest Match SubString

function getLongestMatchingSubstring($str1, $str2){    $len_1 = strlen($str1);    $longest = '';    for($i = 0; $i < $len_1; $i++){        for($j = $len_1 - $i; $j > 0; $j--){            $sub = substr($str1, $i, $j);            if (strpos($str2, $sub) !== false && strlen($sub) > strlen($longest)){                $longest = $sub;                break;            }        }    }    return $longest;}