[FFmpeg-devel] [RFC] Sechole in gcc 3.3+ and 4.*

[Uoti Urpala]

On Mon, 2008-04-07 at 15:25 +0200, Michael Niedermayer wrote:
> > > Twos complement addition, subtraction and multiplication are identical to
> > > their unsigned counterparts. That is they form in isomorphism relative to
> > > them.
> > 
> > C does not require that to be true. It does not require signed numbers
> > to be two's complement either.
> 
> It does require the implemention to specifiy it:
> ------
>   J.3 Implementation-defined behavior
> 1 A conforming implementation is required to document its choice of behavior in each of
>   the areas listed in this subclause. The following are implementation-defined:
> ...
> -- Whether signed integer types are represented using sign and magnitude, two's
>    complement, or ones' complement, and whether the extraordinary value is a trap
>    representation or an ordinary value (6.2.6.2).

Yes, but even if the implementation defines the representation of signed
types to be two's complement that still does not require making signed
arithmetic operations work like unsigned.