-Wconversion and signedness

James Antill james@and.org
Wed Jun 30 15:43:00 GMT 1999


Alexandre Oliva <oliva@dcc.unicamp.br> writes:

> On Jun 23, 1999, Alexandre Duret-Lutz <duret_g@epita.fr> wrote:
> 
> > Shouldn't egcs complain with -Wconversion on the following snippet :
> 
> >   unsigned  i = 2;
> >   unsigned  j = -i;
> 
> Nope.  Unary minus, when applied to an unsigned integral value i,
> means unsigned `2^n - i', where `n' is the number of bits in the
> unsigned type.

 I was fairly sure that this was (roughly) 2^n + 1 - i

 ... but really you should substitute 2^n with UINT_MAX or ULONG_MAX
etc.

-- 
James Antill -- james@and.org
If you go to the Third World and find 100 people who have never tasted ketchup
before, you find out two things: one is that people don't actually like tomato
ketchup, the other is that they dislike all ketchups equally. -- Rob Young.



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