Messages in this thread | | | Date | Wed, 21 Sep 2005 08:08:22 -0700 (PDT) | From | "Randy.Dunlap" <> | Subject | Re: A pettiness question. |
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On Wed, 21 Sep 2005, Ustyugov Roman 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? > > > > > > Thanks in advanced. > > > > > > Liyu > > 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. I think of it as a "truth value" predicate (or operator).
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