Re: Edge case conversions, exceptions to IEEE FPA

[Arnold Neumaier <Arnold.Neumaier@xxxxxxxxxxxx>]

Michel Hack schrieb:

> By now it should be clear to everybody that there is no single correct
> way to convert an anonymous Inf to an interval, so the IA environment
> must provide the means for the programmer (who may know) to choose, and
> in the absence of any knowledge, Empty is the only sensible choice for
> the "ordinary" conversion function, intval(x) (called interval(x) in
> Arnold's 1788.proposal).
>
> Perhaps Siegfried can make a case that intval(x) should be the one that
> converts Inf to Tail, and propose a different function that returns Empty,
> or perhaps intval(x,m) should have a second "mode" argument that does the
> selection -- but then one still has to define implicit conversions.
>
> Sorry, but at this point I still prefer Arnold's approch, though I welcome
> the arrival of the realHull() function.

Namely the following addition to my proposal:

There is an operation realHull(l,u) that returns
for two floating-point numbers l and u the interval [l',u']
with
    l' = NaN, u' = NaN                            if l or u is NaN,
    l' = min(l,u,HUGEPOS), u' = max(l,u,HUGENEG)  otherwise
where HUGEPOS and HUGENEG are the finite floating-point numbers
closest to +inf and -inf.


Arnold Neumaier