php如何生成UUID

if (!function_exists('uuid')) {
function uuid() {
    if (function_exists ( 'com_create_guid' )) {
        return com_create_guid ();
    } else {
        mt_srand ( ( double ) microtime () * 10000 ); //optional for php 4.2.0 and up.随便数播种，4.2.0以后不需要了。
        $charid = strtoupper ( md5 ( uniqid ( rand (), true ) ) ); //根据当前时间（微秒计）生成唯一id.
        $hyphen = chr ( 45 ); // "-"
        $uuid = '' . //chr(123)// "{"
            substr ( $charid, 0, 8 ) . $hyphen . substr ( $charid, 8, 4 ) . $hyphen . substr ( $charid, 12, 4 ) . $hyphen . substr ( $charid, 16, 4 ) . $hyphen . substr ( $charid, 20, 12 );
        //.chr(125);// "}"
        return $uuid;
    }
}}