Re: A pettiness question.

[Fawad Lateef <fawadlateef@gmail.com>]

On 9/21/05, Ustyugov Roman <dr_unique@ymg.ru> wrote:
> > Hi, All.
> >
> >     I found there are use double operator ! continuously sometimes in
> > kernel.
> > e.g:
> >
> >     static inline int is_page_cache_freeable(struct page *page)
> >     {
> >         return page_count(page) - !!PagePrivate(page) == 2;
> >     }
> >
> >     Who would like tell me why write like above?
> 
> For example,
> 
>         int test = 5;
>         !test will be  0,  !!test will be 1.
> 
> This give a enum of {0,1}. If test is not 0, !!test will give 1, otherwise 0.
> 
> Am I right?

Yes, but what abt the above case/example ??? PagePrivate is defined as
test_bit and test_bit will return 0 or 1 only ...... So y there is (
!! )  ??

-- 
Fawad Lateef