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Re: Alternate floating-point results under directed rounding



Baker, Arnold, P1788 members

On 6 Nov 2008, at 15:52, R. Baker Kearfott wrote:
That sounds good.  We'll see what people think as
we read and digest it.

Baker

Arnold Neumaier wrote:
R. Baker Kearfott schrieb:

Without accepting or refuting these arguments, I repeat
that, in the absence of compelling or strong reasons,
it is better to design an interval standard that is
consistent with the IEEE floating point standard.
Parts 1-5 of my proposal (Version 2.0) are fully consistent
with the IEEE 754 floating point standard and probably with
any future revision of it.
However, if we do supply strong arguments, particularly
on the fundamental or mathematical level, this may convince
floating point committee members to make a change in
the next 754 revision.  (Note, though, that it is uncertain
when such a subsequent revision will take place.)
The final
     Part 6: Useful directed rounding properties
of my proposal describes desirable deviations from IEEE 754 ...

This may be a valuable addition. But note
- To make cset implementations easier requires a different set 
  of changes to P754 behaviour, e.g.
    +oo /dn +oo = 0,  +oo /up +oo = +oo,
  where /dn, /up mean division with rounding down and up
  respectively.
  This change-set also should be included in such a section
  of the text.

- Ensure any such requests are for a mathematical reason,
  rather than to aid a particular algorithmic way of doing
  things, which might be superseded by a better one.

John


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