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

Uoti Urpala uoti.urpala
Mon Apr 7 15:32:25 CEST 2008

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 (

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.

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