linux-kernel - Re: [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and &

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Date:	Wed, 5 Mar 2008 07:38:42 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Julia Lawall <julia@...u.dk>
Cc:	yi.zhu@...el.com, linux-wireless@...r.kernel.org,
	ipw3945-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org,
	Harvey Harrison <harvey.harrison@...il.com>,
	Alexander Viro <viro@....linux.org.uk>,
	linux-sparse@...r.kernel.org, Josh Triplett <josh@...edesktop.org>
Subject: Re: [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct
	use of ! and &


* Julia Lawall <julia@...u.dk> wrote:

> From: Julia Lawall <julia@...u.dk>
> 
> In commit e6bafba5b4765a5a252f1b8d31cbf6d2459da337, a bug was fixed 
> that involved converting !x & y to !(x & y).  The code below shows the 
> same pattern, and thus should perhaps be fixed in the same way.

>  	if (sta_ht_inf) {
>  		if ((!sta_ht_inf->ht_supported) ||
> -		   (!sta_ht_inf->cap & IEEE80211_HT_CAP_SUP_WIDTH))
> +		   (!(sta_ht_inf->cap & IEEE80211_HT_CAP_SUP_WIDTH)))
>  			return 0;

i'm wondering, could Sparse be extended to check for such patterns? 

People are regularly running "make C=1" and are sending fixes to make 
entire subsystems sparse-warning-free, so Sparse is a nice mechanism 
that works and it keeps code clean in the long run.

I dont think the "!X & Y" pattern is ever used legitimately [and even if 
it were used legitimately, it's easy to avoid the sparse false positive 
- while in the buggy case we have a clear bug].

	Ingo
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