Re: DirectedInf

["Nate Hayes" <nh@xxxxxxxxxxxxxxxxx>]

Arnold Neumaier wrote:
> Nate Hayes wrote:
> > Arnold Neumaier wrote:
> > > After carefully checking the statements in the standard,
> > > I am sure that one can make things 754-conforming by defining the
> > > new concept of an interval-point format, which agrees with the 
> > > floating-point format on finite reals but differs on the treatment
> > > of inf and NaN. Then none of the constraints on floating-point data 
> > > apply for interval-point data.
> > >
> > > But the same hardware can be used with a switch of rounding modes,
> > > and the exceptions can be handled as required for fast interval support.
>
> > One thing that still worries me is that in Vienna Proposal it appears the 
> > method requires that -0 and +0 are not aliases of each-other.
>
> Why is that an obstacle?

Because many years ago we tried developing an interval library that followed 
these concepts, e.g., [-0,+0], [-0,-0], [+0,+0] were invalid constructions 
and intervals like [-0,3] and [+0,3] were not equivalent aliases of the 
interval [0,3].

This is a Pandora's box, and was an implementation nightmare.

I'm not going back there.

Even if P1788 standardized these conventions, we simply would not use it.

For me, personally, it is a deal-breaker.

My suggestion is to try making DirectedInf depend _entirely_ on the rounding 
modes and not on the signs of the zeros. If you can do this, then I think 
you may have a chance at a good design.

Nate Hayes