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Re: DirectedInf

Dan Zuras Intervals wrote:

Date: Sat, 09 Oct 2010 11:51:06 +0200
From: Arnold Neumaier <Arnold.Neumaier@xxxxxxxxxxxx>
To: Nate Hayes <nh@xxxxxxxxxxxxxxxxx>
CC: Dan Zuras Intervals <intervals08@xxxxxxxxxxxxxx>, stds-1788@xxxxxxxxxxxxxxxxx 
Subject: Re: DirectedInf

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?


	Well, you know I disapprove of creating new values for NaNs.

	But as far as 754 is concerned, so long as the arithmetic
	for zero is done as specified & +0 compares equal to -0,
	I don't see a problem.


Are there requirements on the behavior of +-0 that must be respected
for arbitrary rounding modes (i.e., beyond the modes specified by 754)?



	On the other hand, I'm not sure where in Vienna the concern
	is written.


See Section 7.8 for the motivation, and Sections 7.[1245] for the
proposed behavior.

I'll reconsider Chapter 7 of the Vienna Proposal in the next few weeks,
trying to make it fully 754 compatible in the light of the nearly but
not fully closed door we had discovered.


Arnold Neumaier