PHP——生成唯一序列号UUID

<?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;
}