Re: gcc 2.95.3/ARM problems comparing with negative

[Toralf Lund <toralf at procaptura dot com>]

Richard Earnshaw wrote:

> On Mon, 2004-11-01 at 11:47, Toralf Lund wrote:
>  
>
> > Richard Earnshaw wrote:
> >    
> >
> > > So I suspect your
> > > problem is the type of one of your arguments, most likely the
> > > declaration of position itself.
> > >
> > >
> > >      
> > No, position is all right. But now that you mention it, ZSTP_MAX_POS is 
> > actually set up via an indirect definition involving "sizeof", following 
> > a recent update. I guess that makes ZSTP_MAX_POS an unsigned, and if I 
> > use an "int" typecast, I do get the correct code. I still don't quite 
> > get it, though. Shouldn't -ZSTP_MAX_POS implicitly be treated as a 
> > signed in any case? I would at least expect either fully signed or fully 
> > unsigned operation; the actual code here seems to be a mixture of bot.
> >    
>
> Negation of an unsigned constant produces an unsigned constant.  The
> rules for unsigned arithmetic are precise and work on operations being
> done modulo the 2^bit-size of the data type (unsigned int in this case):
> so -X on an unsigned type is in effect (2^32 - X) on ARM.  On top of
> this, the rules for a combination of signed and unsigned of the same
> bit-size are that the operands are all converted to unsigned first.
>  
OK. If you say so. Strange how long you can know a language without 
noticing those details... But of course, my native compiler (also gcc) 
will actually warn about "comparison between signed and unsigned", at 
least with C++ (which I otherwise normally use), so I'll usually insert 
explicit type conversions when necessary, or otherwise rewrite the code 
to avoid the warning...

- T


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