PHP生成 uuid

//  生成UUID，并去掉分割符
function guid() {
    if (function_exists('com_create_guid')){
        $uuid = com_create_guid();
    }else{
        mt_srand((double)microtime()*);//optional for php 4.2.0 and up.
        $charid = strtoupper(md5(uniqid(rand(), true)));
        $hyphen = chr();// "-"
        $uuid = chr()// "{"
                .substr($charid, , ).$hyphen
                .substr($charid, , ).$hyphen
                .substr($charid,, ).$hyphen
                .substr($charid,, ).$hyphen
                .substr($charid,,)
                .chr();// "}"
    }
    $uuid = str_replace(array('-', '{', '}'), '', $uuid);
    return $uuid;
}