!! is generally used to make the return bool value.
You can use kernelnewbies and linux kernel mailing list.


On Mon, Apr 1, 2013 at 12:43 PM, Ben Wu <crayben@yahoo.cn> wrote:


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


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