密码输入三次锁住

//登录验证
function doLogin()
{
$username = I('username');
$pwd = I('pwd');
//$where = array('username' => $username, 'pwd' => $pwd);
$res = M('admin')->where("username = '$username'")->find();
if(!$res){
$this->error('用户名不存在');
}

//最后登录时间不是当前时间 并且 步长》=0 步长=0
if(date('Ymd') != date('Ymd',$res['last_time']) && $res['log_num'] >= 0){
$res['log_num']=0;
}
//步长》=3 锁定
if($res['log_num'] >= 3){
$this->error('以锁，明天在来吧');
}

if($pwd ==$res['pwd']){
session('user', $res);
if($res['log_num'] > 0){
M('admin')->where('a_id='.$res['a_id'])->save(array('log_num'=> 0));
}
$this->success('登录成功', U('Index/index'));
}else{

//更新步长
$num = $res['log_num'] + 1;
$num_time = array('log_num '=> $num,'last_time'=>time());
M('admin')->where('a_id='.$res['a_id'])->save($num_time);

$i = 2 - $res['log_num'];
$str = "还可以登录".$i.'次';
if($i <= 0) $str ="锁了，明天在来吧";
$this->error($str);
}

}