How to tell if someone is coming from a Tor exit node

tor_functions.php

// http://www.irongeek.com/i.php?page=security/detect-tor-exit-node-in-php
public function IsTorExitPoint(){
    if(gethostbyname(ReverseIPOctets($_SERVER['REMOTE_ADDR']).".".$_SERVER['SERVER_PORT'].".".ReverseIPOctets($_SERVER['SERVER_ADDR']).".ip-port.exitlist.torproject.org")=="127.0.0.2") {
        return true;
    } else {
        return false;
    } 
}

private function ReverseIPOctets($inputip){
    $ipoc = explode(".",$inputip);
    return $ipoc[3].".".$ipoc[2].".".$ipoc[1].".".$ipoc[0];
}