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From: Ingo Molnar <mingo@elte.hu>
To: Bart Van Assche <bart.vanassche-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: Julia Lawall <julia-dAYI7NvHqcQ@public.gmane.org>,
	Christopher Li <sparse-55XgFHCVCFZAfugRpC6u6w@public.gmane.org>,
	yi.zhu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org,
	linux-wireless-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	ipw3945-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	kernel-janitors-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Harvey Harrison
	<harvey.harrison-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Alexander Viro <viro-rfM+Q5joDG/XmaaqVzeoHQ@public.gmane.org>,
	linux-sparse-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Josh Triplett <josh-CC+yJ3UmIYqDUpFQwHEjaQ@public.gmane.org>
Subject: Re: [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct
Date: Wed, 05 Mar 2008 12:36:42 +0000	[thread overview]
Message-ID: <20080305123641.GA2365@elte.hu> (raw)
In-Reply-To: <e2e108260803050430o317d3e0dyed50e86cc4569746-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>


* 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

WARNING: multiple messages have this Message-ID (diff)
From: Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>
To: Bart Van Assche <bart.vanassche-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: Julia Lawall <julia-dAYI7NvHqcQ@public.gmane.org>,
	Christopher Li <sparse-55XgFHCVCFZAfugRpC6u6w@public.gmane.org>,
	yi.zhu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org,
	linux-wireless-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	ipw3945-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	kernel-janitors-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Harvey Harrison
	<harvey.harrison-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Alexander Viro <viro-rfM+Q5joDG/XmaaqVzeoHQ@public.gmane.org>,
	linux-sparse-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Josh Triplett <josh-CC+yJ3UmIYqDUpFQwHEjaQ@public.gmane.org>
Subject: Re: [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and &
Date: Wed, 5 Mar 2008 13:36:42 +0100	[thread overview]
Message-ID: <20080305123641.GA2365@elte.hu> (raw)
In-Reply-To: <e2e108260803050430o317d3e0dyed50e86cc4569746-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>


* Bart Van Assche <bart.vanassche-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 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
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WARNING: multiple messages have this Message-ID (diff)
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 &
Date: Wed, 5 Mar 2008 13:36:42 +0100	[thread overview]
Message-ID: <20080305123641.GA2365@elte.hu> (raw)
In-Reply-To: <e2e108260803050430o317d3e0dyed50e86cc4569746@mail.gmail.com>


* 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

  parent reply	other threads:[~2008-03-05 12:36 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-26 20:44 [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of Julia Lawall
2008-02-26 20:44 ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Julia Lawall
2008-02-26 22:47 ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of.and & Tomas Winkler
2008-02-26 22:47   ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Tomas Winkler
2008-02-27  0:59   ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct John W. Linville
2008-02-27  0:59     ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & John W. Linville
     [not found] ` <Pine.LNX.4.64.0802262143570.18200-QfmoRoYWmW9knbxzx/v8hQ@public.gmane.org>
2008-03-05  6:38   ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct Ingo Molnar
2008-03-05  6:38     ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Ingo Molnar
2008-03-05  6:38     ` Ingo Molnar
2008-03-05  6:49     ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of.and & Christopher Li
2008-03-05  6:49       ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Christopher Li
2008-03-05  7:02       ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct Ingo Molnar
2008-03-05  7:02         ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Ingo Molnar
     [not found]         ` <20080305070201.GA32434-X9Un+BFzKDI@public.gmane.org>
2008-03-05  7:09           ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct Harvey Harrison
2008-03-05  7:09             ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Harvey Harrison
2008-03-05  7:09             ` Harvey Harrison
2008-03-05  8:19             ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct Ingo Molnar
2008-03-05  8:19               ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Ingo Molnar
     [not found]               ` <20080305081904.GA17789-X9Un+BFzKDI@public.gmane.org>
2008-03-05 12:13                 ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct Derek M Jones
2008-03-05 12:13                   ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Derek M Jones
2008-03-05 12:13                   ` Derek M Jones
2008-03-05  8:55           ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct Julia Lawall
2008-03-05  8:55             ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Julia Lawall
2008-03-05  8:55             ` Julia Lawall
2008-03-05 12:20             ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct Ingo Molnar
2008-03-05 12:20               ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Ingo Molnar
     [not found]               ` <20080305122010.GA999-X9Un+BFzKDI@public.gmane.org>
2008-03-05 12:30                 ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of.and & Bart Van Assche
2008-03-05 12:30                   ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Bart Van Assche
2008-03-05 12:30                   ` Bart Van Assche
     [not found]                   ` <e2e108260803050430o317d3e0dyed50e86cc4569746-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2008-03-05 12:36                     ` Ingo Molnar [this message]
2008-03-05 12:36                       ` Ingo Molnar
2008-03-05 12:36                       ` Ingo Molnar
2008-03-05 12:35                 ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct Julia Lawall
2008-03-05 12:35                   ` [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and & Julia Lawall
2008-03-05 12:35                   ` Julia Lawall

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