[Numeric-interest] reproducible floating-point results and 754R

[David Hough 754R work]

For those who have not been following 754R's progress, it's currently
in the sponsor ballot and review phase.      The ballot review committee
is currently debating the issue of whether reproducible results should be
available to programmers who want them (and are willing to pay whatever
performance price is required).

754 said 

 When restricted to a declared subset of the standard,
 these programs should produce identical results on all
 conforming systems

but this was never true, as expression evaluation was never specified.
But most persons whose expertise lies outside the numeric area 
assumed incorrectly that 754 delivered what it promised.    Just a few
of the ways that they were wrong are outlined in Doug Priest's paper

 http://www.validlab.com/goldberg/addendum.html

People who have been active in numerical work sometimes come to believe
that reproducible results are not possible or even not desirable.

The current draft of 754R is expresses its aims this way:

 For operations specified in the normative part of this standard, 
 numerical results and exceptions are uniquely determined by the values of the 
 input data, the operation, and the destination, all under user control.

 Together with language controls it should be possible to write programs 
 that produce identical results on all conforming systems.

There is some sentiment that this language should be removed, although it
was part of the 754R working group's charter from the IEEE.

The current draft is not publicly available, but the last public draft
is at

 http://754r.ucbtest.org/drafts/archive/2006-09-17.pdf



I have written some arguments in favor of requiring conforming 
implementations to provide means to obtain reproducible results at

 http://754r.ucbtest.org/msc-ballots/repro.html

I welcome comments from language designers and mathematical software
programmers.     They could also be sent to Bob Davis, bob at scsi.com,
chair of the IEEE MSC which chartered 754R.




My other commentary on 754R ballot reviews is at

 http://754r.ucbtest.org/msc-ballots/ballot3.html

and encompasses other issues beyond reproducibility.