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, !! converts {zero,not-zero} to {0,1} which is useable
in arithmetic.
--
Eyal Lebedinsky ([email protected]) <http://samba.org/eyal/>
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