Re: floats and intervals, constants, 0.1, 1e400 and Inf
On Mon, 2008-11-10 at 06:32 -0800, R. Baker Kearfott wrote:
>
> > > Now, one concept that has not been discussed so far is whether there
> > > can be several interval types, with different precisions. If so, there
> > > would have to be conversion functions between interval types as well.
> >
> > This is another issue not considered in my proposal.
> >
> > The correct conversion would be by outward rounding the bounds.
> >
>
> Again, in what context? Also, using other than 754 types would
> complicate 1788's task. We should consider what it would gain us
> if we did so.
The proposal from IFIP WG 2.5 to P754 preferred that intervals be
provided with bounds represented by all types the implementor of 754
provided. Conversion between interval representations was not
addressed, bug should have been. Rounding the bounds outward seems like
the only sensible definition, unless one knows for sure that one or the
other bound is exact. Providing conversions with flags that indicate
that one or the other bound is exact seems like too much complication,
at least for a first edition standard.
Constructors of intervals from pairs of FP numbers are obviously needed.
In this context, should the FP numbers be considered to be exact? If
only constructors that take the same type bounds are offered, and can
only produce intervals having a representation consisting of the two FP
given numbers, there is no need to consider whether one or the other
bound is inexact. Presumably, if one decomposes an interval into two FP
numbers, however, and then converts those FP numbers to a different
precision, and then re-composes them into an interval, it would be
desirable to round (or not) each one correctly. I think P754 can
already convert from one precision to another with directed rounding.
--
Van Snyder | What fraction of Americans believe
Van.Snyder@xxxxxxxxxxxx | Wrestling is real and NASA is fake?
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