[Cfp-interest 2602] Re: draft CFP response for NB comments and N3071

[Jim Thomas]

If I receive any more additions or correction by noon PST tomorrow (Monday, January 9), I will try to incorporate them into the document I submit to WG14 (before the 2-week deadline).

- Jim Thomas


> On Jan 7, 2023, at 9:51 AM, Jim Thomas <jaswthomas at sbcglobal.net> wrote:
> 
> Here’s an update to the draft, intended to address the issues raised by Joseph. Added or changed text is highlighted.
> 
> https://wiki.edg.com/pub/CFP/WebHome/CFP_review_of_NB_comments-20230107.pdf
> 
> - Jim Thomas
> 
>> On Jan 6, 2023, at 6:03 PM, Joseph Myers <joseph at codesourcery.com> wrote:
>> 
>> On Fri, 6 Jan 2023, Jim Thomas wrote:
>> 
>>>> GB-164: I'll disagree with the disagreement here (I assume this will end 
>>>> up needing to be discussed in the WG14 meeting), since the semantic change 
>>>> in C2x (which I don't think was ever explicitly discussed as an intended 
>>>> semantic change in a paper) would make errno-setting implementations of 
>>>> various functions much more complicated and less efficient - detecting 
>>>> overflow after the fact (in a way that's valid for previous versions of C) 
>>>> by checking for an infinite results from finite arguments is very 
>>>> straightforward, determining based on the arguments whether pow, fdim, 
>>>> hypot or fma (for example) would overflow / whether a result of the 
>>>> largest finite value is an overflow is much more complicated and 
>>>> inefficient (and saving and restoring exceptions so as to test, for the 
>>>> purposes of errno setting, whether the overflow exception was raised, is 
>>>> also inefficient; such explicit manipulations of floating-point state are 
>>>> liable to empty the processor pipeline).  (This concern is specifically 
>>>> about errno setting rather than exceptions; ensuring the overflow 
>>>> exception is raised for overflow to a finite number isn't a problem in the 
>>>> same way.  
>>> 
>>> Could you determine overflow errno setting from the overflow 
>>> floating-point exception?
>> 
>> See above.  If a function has to save and restore floating-point state 
>> explicitly, it's liable to be bad for pipelined execution (so efficiency).  
>> (And the "save and restore" part is necessary, since the overflow flag 
>> might already be raised on entry to the function.)
>> 
>>>> GB-279: The wording of some of the changes isn't quite right (constexpr 
>>>> isn't a storage *duration*, so wording shouldn't refer to it as such in 
>>>> F.8.4 or F.8.5).
>>> 
>>> Rewordings might be:
>>> 
>>> In F.8.4 #1 change “for an object that has static or thread storage 
>>> duration” to “for an object declared with storage-class specifier 
>>> constexpr, static, or thread_local”.
>> 
>> That's not correct.  An object with static storage duration might have no 
>> storage-class specifier, or only the extern specifier, if at file scope.
>> 
>>> In F.8.5 #1 change “of objects that have static or thread storage 
>>> duration” to “of objects declared with storage-class specifier 
>>> constexpr, static, or thread_local”.
>> 
>> Likewise.
>> 
>> -- 
>> Joseph S. Myers
>> joseph at codesourcery.com
> 

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