Proposed reposting of agenda item #21

[Fred Zemke <fred.zemke@xxxxxxxxxx>]

agenda item #21 in http://754r.ucbtest.org/motions.html#21
has no embedded newlines and consequently every sentence
runs off the edge of the page when I print it or view.
I have reformatted it within 70 characters per line.
I request that this be substitued into 
http://754r.ucbtest.org/motions.html#21
Thanks
Fred

Agenda item #21

Date: Thu, 3 Aug 2006 17:05:08 -0700
From: "Tsen Jr, S Charles"
Subject: [Stds-754] Clarify decimal encoding of NaN's

Motion:
=======
Clarify decimal NaN encoding of payloads in Section 5.5. The new
text makes some assumptions, where the old text left holes.


Rationale:
==========
The draft's description of the payload for NaN's seems a bit
abstruse to me. Particularly, it seems to leave a few questions
regarding canonical/non-canonical NaN's. I've rewritten it below,
but am open to any guidance or edits.

Issue1:
-------
The draft states (on page21, section 5.5, bullet a, paragraph 2)
"A canonical NaN representation has bits G6 through Gw+4 zero,
and the trailing significand T is canonical ..."

Why doesn't the draft mention anything about non-canonical NaN's?
This would lead me to assume that any of the following (1) there
is no such thing as a non-canonical NaN or (2) that non-canonical
NaN's may exist, but are illegal or (3) non-canonical NaN's are
interpreted as 0 or (4) non-canonical NaN's are interpreted as
NaN's with a payload of 0.

Whatever the case, it should be stated.

Issue2:
-------
The draft states (on page21, section 5.5, bullet a, paragraph 1)
"The remaining bits of G together with T (encoded as for finite
numbers below) distinguish various NaN's."

If it's true that NaN's are encoded as finite numbers, it must
have a 100(binary) prepended to the significand, since its
steering bits {G0, G1} == 11(binary), which seems unnecessarily
confusing.


Text:
=====

Replace:
--------
"If G0 through G4 are 11111, then r is qNaN or sNaN and v is NaN
regardless of S. The remaining bits of G together with T (encoded
as for finite numbers below) distinguish various NaNs. If G5 is 1,
then r is sNaN; otherwise r is qNaN.

A canonical NaN representation has bits G6 through Gw+4 zero, and
the trailing significand T is canonical, with the maximum value
for the payload of a canonical NaN therefore being 10(3×J) − 1."

With:
-----
"If G0 through G4 are 11111, then v is NaN regardless of S.
Furthermore, if G5 is 1, then r is sNaN; otherwise r is qNaN.
The remaining bits of G together with T constitute the NaN's
payload, which helps distinguish it from other NaN's.

The NaN payload has an exponent and a significand field
identical to finite numbers below. These fields are encoded
similarly, except assuming G0 and G1 together are NOT 11."

A NaN can be either canonical or non-canonical. It is canonical
if bits G6 through Gw+4 are zero and T is canonical. If it is
non-canonical "