Motion P1788/M0014.01: 6.1_and_6.2_of_document: NO
I vote NO on motion 14. I would vote yes if:
1. The empty set representation was defined.
It's necessary for a receiver can know when a set is empty.
2. The empty set representation is some form other than (NaN, NaN).
Implementing this using 754 hardware is too expensive. A special case like empty should be detectable by a single compare and branch, and that is not possible with NaN.
Also, "NaN" does not specify whether it is Quiet or Signaling, and other parts of the text allow Signaling. Doing a standard compare on a Signaling NaN raises an Invalid exception, and on most systems if exceptions are enabled that will trap. Other ways of checking for a Signaling NaN are too expensive.
Since we have not imposed the requirement that the floating point representation be IEEE 754, we shouldn't do it by the back door by requiring the use of NaN. (Yes, I've argued allowing (-oo, +oo) and will continue to. There's a difference between allowing and requiring. Maybe the intent of the motion was to allow not require NaN, but if "When x is the empty set, x and x are taken as NaN. Whether qNaN or sNaN is used, and any payload, are implementation-defined." isn't intended to require the use of NaN, it needs to be reworded.
3. The requirement that 0 be represented as +0 be removed.
There's no need for this, and it forces unnecessary overhead. That overhead is not just when the data will be interchanged - often that is unknown when it is calculated, so the overhead will almost always occur for no benefit. Whether the sign of a zero can convey information relevant to intervals isn't the issue - imposing unnecessary costs is.
4. The Decimal description is improved.
Eg, does the requirement that 0 be represented as +0 and making the choice of which cohort of a value be implementation defined mean that all but one of the many precisions of zero (0., 0.0, 0.00, etc) are prohibited? Which one would be allowed?
I think the intent is likely right, but the wording needs clarification.
- Ian McIntosh IBM Canada Lab Compiler Back End Support and Development
Ralph Baker Kearfott ---05/13/2010 05:07:56 PM---P-1788: The discussion period for this motion has run its course,
From: |
Ralph Baker Kearfott <rbk@xxxxxxxxxxxx> |
To: |
Ian McIntosh/Toronto/IBM@IBMCA |
Date: |
05/13/2010 05:07 PM |
Subject: |
Motion P1788/M0014.01: 6.1_and_6.2_of_document: up for vote |
P-1788:
The discussion period for this motion has run its course,
and we have not received amendments. Therefore, the motion
is entering its three-week voting period. Voting will continue
until after the end June 3, 2010. The motion is appended
to this email. Please note that the two-thirds majority
rule (along with the quorum rule), as well as the explanation
of "no" votes rule, are in effect for voting on this motion.
(The idea is that, if the motion fails, we can re-start
the vote when beneficial changes are implemented.)
William / Juergen: Please record this action in the minutes.
I offer thanks for the previous and continuing work of all
involved.
Sincerely,
Baker
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Proposer: Dan Zuras
Second: Bo Einarsson
Motion:
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The text in sections 6.1 and 6.2 of the current draft, Version
02.2, of the draft P1788 standard text shall be accepted as
official text of the standard. Please note the following.
1. A two thirds majority is required for this motion to pass.
2. The text will be revised as a whole in approximately July
2011; thus the decision to accept this text does not set it
in stone. A revision to accepted text will not be made before
then (except for removing typos) unless a clear inconsistency
in the text is uncovered.
3. Following our procedures, a NO vote to this motion should be
accompanied by a description of the changes that would enable
the voter to vote YES.
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R. Baker Kearfott, rbk@xxxxxxxxxxxxx (337) 482-5346 (fax)
(337) 482-5270 (work) (337) 993-1827 (home)
URL: http://interval.louisiana.edu/kearfott.html
Department of Mathematics, University of Louisiana at Lafayette
(Room 217 Maxim D. Doucet Hall, 1403 Johnston Street)
Box 4-1010, Lafayette, LA 70504-1010, USA
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