X-Spam-Check-By: sourceware.org To: cygwin@cygwin.com From: Yitzchak Scott-Thoennes Subject: Re: cygwin source question Date: Mon, 22 Jan 2007 08:19:19 +0000 (UTC) Lines: 23 Message-ID: References: <20070121143731.GC25379@ns1.anodized.com> <009401c73d79$4cf91d40$a501a8c0@CAM.ARTIMI.COM> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit User-Agent: Loom/3.14 (http://gmane.org/) X-IsSubscribed: yes Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Delivered-To: mailing list cygwin@cygwin.com Dave Korn writes: > On 21 January 2007 14:38, Christopher Layne wrote: > > I notice in some places, there are double-negates, like: > > > > me->read_ready |= ret || !!(events & (FD_READ | FD_ACCEPT | FD_CLOSE)); > > > > What's the rationale for these? To enforce either a 0 or 1, to be directly > > in line with boolean, rather than a zero or non-zero result? > > It's a standard C idiom for that, yeh, it normalizes zero/non-zero into 0/1. Also protects against accidentally truncating true values to false (e.g. if events is an int and events |(FD_READ...) is 0x80000000 and me->read_ready is a short, the implicit cast to short in the assignment turns 0x80000000 into 0). This is also a Perl idiom (though Perl doesn't suffer the above problem). Some people prefer (expr) ? 1 : 0, which looks a lot worse to me than !!(expr). -- I'm looking for a job: http://perlmonks.org/?node=ysth#looking -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Problem reports: http://cygwin.com/problems.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/