gistfile1.php

<?php

$arguments = xmlrpc_decode_request($xml, $method);

switch($method) {
    case 'get_topic':
        $_GET['forum_id']  = $arguments[0];
        $_GET['start_num'] = $arguments[1];
        $_GET['last_num']  = $arguments[2];
        $_GET['mode']      = $arguments[3];
        break;
}

$method();