what does it use two "!!"

April 1, 2013

      Dear All：
1> I found some placeuse two "!!", what's means 
    if(button->gpio != INVALID_GPIO)
        state = !!((gpio_get_value(button->gpio) ? 1 : 0) ^ button->active_low);
    else
        state = !!button->adc_state;

2> is there some MSN group to study linux kernel or discuss it ?

Thanks and Best Regards

Ben Wu

MSN:crayben@yahoo.cn