[cfp-interest 3596] Re: Annex F Changes Discussion Paper

[Jim Thomas]

Some comments on https://wiki.edg.com/pub/CFP/WebHome/C2Y-Discussion-AnnexF-20250826.pdf follow.

1.
> nextafter(x, y) raises the "underflow" floating−point exception when x ≠y
> and the result is zero or subnormal


Disambiguation of whether “and the result is zero or subnormal” is a qualification or a consequence depends on knowing the form.

Did you consider the form

	qualification: …

2.
> Notes that some of these cases refer to odd and not odd, integer n, while others refer to odd and even, where
> the latter implies that 0 is a positive even number. Except for that implication, it is tempting to leave them
> alone. But essentially, this consistency is unresolved. Suggestions?


Indicating specific cases would be helpful for understanding the issue.

3.
> Here Annex F currently relies (without explanation) on the implication of an inclusive upper bound of positive infinity. To avoid this lack of clarity, 


What’s not clear? Is it not clear that positive infinity is greater than 0?

4.
> Its negation, i.e., is not a NaN, also appears.


Yes, this is a problem, given that NaN generally means quiet NaN.

5.
> Consistency will be enforced by ensuring that the use of NaN in such cases always appear with both the ’is’
> and the indefinite article.


“x is a NaN” reads better after “if” or “when”. “x a NaN” reads better after “for”. Why not incorporate that be the rule?

6.
> The mathematical domain which covers all of those eight cases is the combination of (2) and (4):
> 
> 	(8)	0 ≤ |x| ≤ ∞ or x is a NaN


If we change F.2.2 #3:

——
This annex does not require the full support for signaling NaNs specified in ISO/IEC 60559. This annex uses the term NaN, unless explicitly qualified, to denote quiet NaNs.
——

to something like:

-----
This annex does not require the full support for signaling NaNs specified in ISO/IEC 60559. Signaling NaNs are generally excluded from the specification. Unless explicitly stated otherwise, phrases such as “for all x” do not include signaling NaNs, and the term “NaN" denotes only quiet NaNs.
——

then (8) could be replaced by “all x”.

The change would also give a fuller characterization of the status of signaling NaNs in the annex.



> On Aug 26, 2025, at 12:09 AM, Damian McGuckin <damianm at esi.com.au> wrote:
> 
> On Thu, 7 Aug 2025, Damian McGuckin wrote:
> 
>> Please find uploaded to the Wiki
>> 
>>  https://wiki.edg.com/pub/CFP/WebHome/C2Y-Discussion-AnnexF-20250807.pdf
>> 
>> It discusses the detail and background of some of the changes I propose for Annex F, in particular a rigorous syntax for all special cases and
>> the domains associated with them.
> 
> A revision has been uploaded, incorporating Jim's recomendations.
> 
>   https://wiki.edg.com/pub/CFP/WebHome/C2Y-Discussion-AnnexF-20250826.pdf
> 
> Thanks - Damian
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