如何生成绝对唯一且不容易被猜测的推荐码

<code class="php">function makeCode($t) {
  $time = $t.mt_rand(10,99); // 要是觉得不够可以加上线程ID等。
  $ce = $time[9];
  $xy = array();
  $xy[0] = array('A','F','D','X','G','H','K','U','P','Y','W','P');
  $xy[1] = array('R','G','H','P','X','D','Y','U','K','F','S','Z');
  // ... 不重复的序列即可
  $xy[9] = array('S','K','T','U','E','Q','V','G','R','X','C','J');
  $rb = '';
  for ($i = 12;$i--;) {
    $rb .= $xy[$ce][$time[$i]];
  }
  return $rb;
}

makecode(time())</code>

<code>echo file_get_contents('/proc/sys/kernel/random/uuid');
// 输出: 6c509fc7-328b-4d82-9af8-60c44e7b84b4</code>

<code>echo substr(md5(uniqid(mt_rand(1000, 9999), true)), 20);
// 输出:1c7a6db616de </code>

<code>echo bin2hex(openssl_random_pseudo_bytes(16));
// 输出: 5a8a80e06ffe44fd0a6931707a26f0cc</code>