Re: unsigned / double propagation weirdness?

[Richard Guenther <rguenth at tat dot physik dot uni-tuebingen dot de>]

Robert Dewar wrote:
> Giovanni Bajo wrote:
>
> > > you certainly don't want to regard the use of unary
> > > minus on unsigned as something you warn about.
>
>
> > What's the rationale for this? I know that other compilers do 
> > implement this
> > warning and I indeed found it useful in the past.
>
>
> To me, unary minus on unsigned is both useful, and has a clear and 
> expected meaning (take the twos complement). I would find it most
> irritating to get warnings on this. If it is really the case that
> many/most C programmers are bamboozled by this standard usage in
> the language, perhaps there is an argument for a warning that can
> be turned on, but I certainly would not want to see this in -Wall.

Well, if it's not in -Wall, nobody will actually use it and it will not 
help finding bugs.  The warning should probably be only, if inside
a mixed signed/unsigned expression (where float counts as signed of 
course).  I.e. for completely unsigned expression we should not warn.

Richard.