<?php function uuid($uid = '')
{
$chars = md5(uniqid(mt_rand(), true));
$uuid = substr($chars, 0, 8).'-';
$uuid .= substr($chars, 8, 4).'-';
$uuid .= substr($chars, 12, 4).'-';
$uuid .= substr($chars, 16, 4).'-';
$uuid .= substr($chars, 20, 12);
return $uid . $uuid;
}