Re: A pettiness question.

From: Fawad Lateef
Date: Wed Sep 21 2005 - 04:01:33 EST


On 9/21/05, Ustyugov Roman <dr_unique@xxxxxx> 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
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