[Cfp-interest 2234] Re: contradiction about the INFINITY macro

[Jim Thomas]

The draft proposal for this 

https://wiki.edg.com/pub/CFP/WebHome/C23_proposal_-_Contradiction_about_INFINITY_macro-20211010.pdf

takes a different approach. I’m not sure which is better. We will decide on what to submit to WG14 at the CFP meeting this week.

- Jim Thomas

> On Oct 5, 2021, at 11:13 AM, Jim Thomas <jaswthomas at sbcglobal.net> wrote:
> 
> I suggest changing 
> 
> 	else to a positive constant of type float that overflows at translation time
> 
> to
> 
> 	else to an expression of type float that overflows with positive sign at translation time
> 
> This is intended to allow the implementation to use whatever magic is needed.
> 
> I had lost track of this issue and neglected to put it on the September CFP agenda. If we can converge on a resolution, and if no one objects, I can submit a paper with our agreed suggested change before the deadline. Please send any comments ASAP.
> 
> - Jim Thomas
> 
>> On Sep 29, 2021, at 6:54 PM, Vincent Lefevre <vincent at vinc17.net> wrote:
>> 
>> I have posted the following to comp.std.c (note: this is a case where
>> float is not an IEEE 754 type, as there are no values representing an
>> infinity):
>> 
>> In ISO C99:TC3 to C17, 7.12p4:
>> 
>> The macro INFINITY expands to a constant expression of type float
>> representing positive or unsigned infinity, if available; else to a
>> positive constant of type float that overflows at translation time.
>> 
>> Consider the "else" case. It is said that INFINITY expands to a
>> constant and that it overflows, so that it is not in the range of
>> representable values of float.
>> 
>> But in 6.4.4p2:
>> 
>> Each constant shall have a type and the value of a constant shall
>> be in the range of representable values for its type.
>> 
>> which would imply that INFINITY expands to a value in the range of
>> representable values of float, contradicted by 7.12p4.
>> 
>> Same issue in the current C2x draft N2596 (7.12p7 and 6.4.4p2).
>> 
>> -- 
>> Vincent Lefèvre <vincent at vinc17.net> - Web: <https://www.vinc17.net/>
>> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
>> Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
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> 
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