php生成UUID

function guid() {
   if (function_exists('com_create_guid')) {
      return com_create_guid();
   } else {
      mt_srand((double)microtime()*10000);
      $charid = strtoupper(md5(uniqid(rand(), true)));
      $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;
   }
}