Re: bug list: assigning negative values to unsigned variables

[Bernd Petrovitsch <bernd@petrovitsch.priv.at>]

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