From: Eyal Lebedinsky <eyal@eyal.emu.id.au>
To: lkml <linux-kernel@vger.kernel.org>
Subject: Re: A pettiness question.
Date: Wed, 21 Sep 2005 18:57:21 +1000 [thread overview]
Message-ID: <43312071.7000809@eyal.emu.id.au> (raw)
In-Reply-To: <200509211200.06274.dr_unique@ymg.ru>
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 (eyal@eyal.emu.id.au) <http://samba.org/eyal/>
next prev parent reply other threads:[~2005-09-21 8:57 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-21 7:49 A pettiness question liyu
2005-09-21 8:00 ` Ustyugov Roman
2005-09-21 8:57 ` Eyal Lebedinsky [this message]
2005-09-21 9:01 ` Fawad Lateef
2005-09-21 9:30 ` Andrea Arcangeli
2005-09-23 2:36 ` Vadim Lobanov
2005-09-21 15:08 ` Randy.Dunlap
2005-09-21 19:11 ` Bill Davidsen
2005-09-21 19:46 Nick Warne
2005-09-21 20:05 ` Vadim Lobanov
2005-09-22 7:10 ` Helge Hafting
2005-09-22 12:21 ` Steven Rostedt
2005-09-22 14:40 ` linux-os (Dick Johnson)
2005-09-22 2:43 ` Fawad Lateef
[not found] <4PiLw-2yn-25@gated-at.bofh.it>
[not found] ` <4Pj4M-3as-1@gated-at.bofh.it>
[not found] ` <4PtnM-1oW-55@gated-at.bofh.it>
[not found] ` <4Pynh-fp-1@gated-at.bofh.it>
2005-09-25 14:38 ` Bodo Eggert
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