From: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
To: Julia Lawall <julia@diku.dk>
Cc: Dan Carpenter <error27@gmail.com>,
kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: bug list: assigning negative values to unsigned variables
Date: Wed, 27 Jan 2010 14:12:49 +0000 [thread overview]
Message-ID: <1264601569.10795.131.camel@localhost> (raw)
In-Reply-To: <Pine.LNX.4.64.1001271329460.20256@ask.diku.dk>
On Mit, 2010-01-27 at 13:30 +0100, Julia Lawall wrote:
> On Wed, 27 Jan 2010, Bernd Petrovitsch wrote:
> > On Mit, 2010-01-27 at 11:57 +0100, Julia Lawall wrote:
> > > On Wed, 27 Jan 2010, Dan Carpenter wrote:
> > >
> > > > Fixing the places which assign negative values to unsigned variables is a good janitor task.
> > >
> > > I had the impression that assignment to -1 was done sometimes as a
> > > portable way to initialize the variable to 0xffff (for any number of f's).
Hmm, perhaps some experienced language lawyer can comment on the
"portable".
> > > So perhaps it is not so trivial to fix.
> > Any particular reason that ~0U, ~0UL, and ~0ULL shouldn't do the same
> > (without relying on conversion from signed to unsigned)?
>
> Then the constant specifies the type?
Yes. And it is necessary as "~0U" assigned to a "unsigned long long int"
won't give "~0ULL".
Otherwise "0" would be a signed int and from then on (starting with
"~0") we are in the C hell of type promotion/conversion from signed to
unsigned and/or back - at least in theory.
Bernd
--
Bernd Petrovitsch Email : bernd@petrovitsch.priv.at
LUGA : http://www.luga.at
WARNING: multiple messages have this Message-ID (diff)
From: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
To: Julia Lawall <julia@diku.dk>
Cc: Dan Carpenter <error27@gmail.com>,
kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: bug list: assigning negative values to unsigned variables
Date: Wed, 27 Jan 2010 15:12:49 +0100 [thread overview]
Message-ID: <1264601569.10795.131.camel@localhost> (raw)
In-Reply-To: <Pine.LNX.4.64.1001271329460.20256@ask.diku.dk>
On Mit, 2010-01-27 at 13:30 +0100, Julia Lawall wrote:
> On Wed, 27 Jan 2010, Bernd Petrovitsch wrote:
> > On Mit, 2010-01-27 at 11:57 +0100, Julia Lawall wrote:
> > > On Wed, 27 Jan 2010, Dan Carpenter wrote:
> > >
> > > > Fixing the places which assign negative values to unsigned variables is a good janitor task.
> > >
> > > I had the impression that assignment to -1 was done sometimes as a
> > > portable way to initialize the variable to 0xffff (for any number of f's).
Hmm, perhaps some experienced language lawyer can comment on the
"portable".
> > > So perhaps it is not so trivial to fix.
> > Any particular reason that ~0U, ~0UL, and ~0ULL shouldn't do the same
> > (without relying on conversion from signed to unsigned)?
>
> Then the constant specifies the type?
Yes. And it is necessary as "~0U" assigned to a "unsigned long long int"
won't give "~0ULL".
Otherwise "0" would be a signed int and from then on (starting with
"~0") we are in the C hell of type promotion/conversion from signed to
unsigned and/or back - at least in theory.
Bernd
--
Bernd Petrovitsch Email : bernd@petrovitsch.priv.at
LUGA : http://www.luga.at
next prev parent reply other threads:[~2010-01-27 14:12 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-27 10:40 bug list: assigning negative values to unsigned variables Dan Carpenter
2010-01-27 10:40 ` Dan Carpenter
2010-01-27 10:57 ` Julia Lawall
2010-01-27 10:57 ` Julia Lawall
2010-01-27 11:09 ` Bernd Petrovitsch
2010-01-27 11:09 ` Bernd Petrovitsch
2010-01-27 12:30 ` Julia Lawall
2010-01-27 12:30 ` Julia Lawall
2010-01-27 14:12 ` Bernd Petrovitsch [this message]
2010-01-27 14:12 ` Bernd Petrovitsch
2010-01-27 14:44 ` Al Viro
2010-01-27 11:13 ` Dan Carpenter
2010-01-27 11:13 ` Dan Carpenter
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