what does it use two "!!"

[Christopher Harvey]

Ben Wu writes:

> 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;

if a = 1010011 then
!a = 0 and
!!a = 1

if a = 000000 then
!a = 1
!! = 0

basically it means if a is non-zero then make a = exactly 1, else leave
it at zero.

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

don't know, but it would be ironic.

> Thanks and Best Regards
>
> Ben Wu
>
> MSN:crayben at yahoo.cn
>
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