php 生成8位数唯一的激活码

 /**
    *生成激活码
    */
    function showGenerationActivationCode(){
    	#渠道类型id
    	$channel_id=$_POST['channel'];
    	#根据渠道id去查询渠道英文名称
        $channelInfo = load_mysql ( "channelInfo" );
        $_res=$channelInfo->getInfoById($channel_id);
        $en_name=$_res['en_name'];
    	#活动类型
    	$type=$_POST['active_type'];
    	#生成数量
    	$nub=$_POST['nub'];
    	#连接redis
		$redis=new Redis();
        $redis->connect('192.168.1.133',8899);
        #授权
        $redis->auth("XXXXXX");
         #存入数据
        for($i=0;$i<$nub;$i++){
	    	 #接受生成的激活码
	    	 $ActivationCode=$this->showunique_rand(10000000,99999999,1);
	    	 #生成code
	    	 $code=$this->showAlgorithm_ActivationCode($type,$channel_id,$ActivationCode);
	    	 #写入redis
             $redis->hmset('hash','code_hash',array('code'=>$code));
        }
        #写入redis
        $redis->hmset('hash', 'channel_hash', array($en_name=> $channel_id ));
        $this->PromptMsg = "生成成功！";
        $this->UrlJump = "./index.php?module=operation&action=ActivationCode&menuId=168";
		$this->promptMsg ();
    }
    /**
    *生成code算法
    *type:活动类型[取前三位]
    *channel_id:渠道id[取前三位,不足以0填充]
    *array_ActivationCode:激活码数组
    *code算法格式=活动类型+渠道id+array_ActivationCode;
    *return code的数组
    */
    function showAlgorithm_ActivationCode($type,$channel_id,$ActivationCode){
    	 #截取活动类型前位字符串
         $type=mb_substr($type,0,3,'utf-8');
         #渠道id[取前三位,不足左边以0填充]
         $channel_id=str_pad($channel_id,3,'0',STR_PAD_LEFT);
         #拼接code
         $code=$type.''.$channel_id.''.$ActivationCode;
         return  $code;
    }
    /**
    *生成8位数的激活码算法
    */
    function showunique_rand($min, $max, $num=1) {
       $count = 0;
       $return = array();
       while ($count < $num) {
        $return[] = mt_rand($min, $max);
        $return = array_flip(array_flip($return));
        $count = count($return);
      }
      return $return[0];
    }