Date: Wed, 5 Mar 2008 13:36:42 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Bart Van Assche <bart.vanassche@gmail.com>
Cc: Julia Lawall <julia@diku.dk>, Christopher Li <sparse@chrisli.org>,
	yi.zhu@intel.com, linux-wireless@vger.kernel.org,
	ipw3945-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org,
	kernel-janitors@vger.kernel.org,
	Harvey Harrison <harvey.harrison@gmail.com>,
	Alexander Viro <viro@ftp.linux.org.uk>,
	linux-sparse@vger.kernel.org, Josh Triplett <josh@freedesktop.org>
Subject: Re: [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct
	use of ! and &
Message-ID: <20080305123641.GA2365@elte.hu> (sfid-20080305_123709_646888_DAE91D9B)
References: <Pine.LNX.4.64.0802262143570.18200@ask.diku.dk> <20080305063842.GA24495@elte.hu> <70318cbf0803042249j57d7f3a3j7666961a9132b10b@mail.gmail.com> <20080305070201.GA32434@elte.hu> <Pine.LNX.4.64.0803050951550.28021@ask.diku.dk> <20080305122010.GA999@elte.hu> <e2e108260803050430o317d3e0dyed50e86cc4569746@mail.gmail.com>
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* Bart Van Assche <bart.vanassche@gmail.com> wrote:

> If someone writes (!x & !y) instead of (!x && !y) because both x and y 
> have to be evaluated, this means that both x and y have side effects.
> Please keep in mind that the C language does not specify whether x or 
> y has to be evaluated first, so if x and y have to be evaluated in 
> that order, an expression like (!x & !y) can be the cause of very 
> subtle bugs. I prefer readability above brevity.

such expressions _must_ be written as:

  ret1 = x();
  ret2 = y();

  if (ret1 && ret2)
	...

any side-effects are totally un-obvious when they are in expressions and 
someone doing cleanups later on could easily change the '&' to '&&' and 
introduce a bug.

	Ingo