<?
$str='%uE8FC%u0044%u0000%u458B%u8B3C%u057C%u0178';
$str=preg_replace('/%u([a-f0-9]{2})([a-f0-9]{2})/i','\\\\x$1\\\\x$2',$str);
echo "$str<br/>";
$str=preg_replace('/\x5Cx([a-f0-9]{2})\x5Cx([a-f0-9]{2})/i','%u$1$2',$str);
echo $str;
?>