From mboxrd@z Thu Jan  1 00:00:00 1970
From: Valdis.Kletnieks@vt.edu
Date: Tue, 29 Jan 2013 15:55:16 +0000
Subject: Re: [patch] TTY: synclink, small cleanup in dtr_rts()
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References: <20130127194039.GA18787@elgon.mountain> <1359317078.14406.12.camel@joe-AO722>
            <20130127201947.GO16282@mwanda>
In-Reply-To: Your message of "Sun, 27 Jan 2013 23:19:47 +0300."
             <20130127201947.GO16282@mwanda>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Joe Perches <joe@perches.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby <jslaby@suse.cz>, Paul Fulghum <paulkf@microgate.com>, David Howells <dhowells@redhat.com>, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org

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On Sun, 27 Jan 2013 23:19:47 +0300, Dan Carpenter said:

> Yeah.  I think it would be, but adding bitflags together instead of
> doing bitwise ORs is very common as well.

The fact it's common doesn't mean it's good programming practice,
or even correct.  Consider:

#define F_FOO 0x01
#define F_BAR 0x02
#define F_BAZ 0x04

unsigned int flags = F_FOO;
...
      flags |= F_BAR;

Now some time later, another code path does this:

      flags += F_FOO;

If it was another |, it would be a no harm no foul class of bug.
But how long is it going to take you to figure out who set F_BAZ?

I wonder if there's a way to write a coccinelle patch to find places
where we do arithmetic operations on bitmasks....

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