[Cfp-interest 2667] Re: floating constants issue

[Jim Thomas]

> On Jan 30, 2023, at 5:51 PM, Vincent Lefevre <vincent at vinc17.net> wrote:
> 
> On 2023-01-30 15:19:52 -0800, Jim Thomas wrote:
>> 6.4.4.2 #8 says:
>> 
>> All floating constants of the same source form 83) shall convert to the same internal format with the same value.
>> 
>> With the FENV_ROUND and FENV_DEC_ROUND pragmas this is no longer true. For example, 7.6.2 #4 for FENV_ROUND says "Floating constants (6.4.4.2) of a standard floating type that occur in the scope of a constant rounding mode shall be interpreted according to that mode."
>> 
>> This was pointed out in a recent email which I was unable to find. Thanks to the sender.
> 
> I posted the remark about 6.4.4.2 #8 in Cfp-interest 2634:
>  http://mailman.oakapple.net/pipermail/cfp-interest/2023-January/002648.html
> 
> But I hadn't noticed the issue with FENV_ROUND.
> 
>> A fix would be to replace the sentence with something like:
>> 
>> All floating constants of the same source form shall convert to the same internal format. All floating constants of the same source form that are subject to the same translation-time rounding direction (either the default or a rounding direction set by an FENV_ROUND or FENV_DEC_ROUND pragma) shall convert to the same internal format with the same value.
>> 
>> or
>> 
>> All floating constants of the same source form shall convert to the same internal format and, provided they are subject to the same translation-time rounding direction (either the default or a rounding direction set by an FENV_ROUND or FENV_DEC_ROUND pragma), to the same value.
> 
> Both are unclear. What if it is set to FE_DYNAMIC?

Maybe

All floating constants of the same source form shall convert to the same internal format and, provided they are subject to the same translation-time rounding direction (either the default or a constant rounding mode other that FE_DYNAMIC set by an FENV_ROUND or FENV_DEC_ROUND pragma), to the same value.

But that would suggest that same-form floating constants could have different values under FE_DYNAMIC. Setting to FE_DYNAMIC should not affect the translation time conversion of floating constants in that they would still get default translation-time rounding.

> 
> BTW, is there a way to restore the static rounding mode when
> outside external declarations? This would be important if one
> wants to use this pragma in a header file.

It can be “restored" to FE_DYNAMIC which serves as a “default”.

- Jim Thomas
> 
> -- 
> 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)
> _______________________________________________
> Cfp-interest mailing list
> Cfp-interest at oakapple.net
> http://mailman.oakapple.net/mailman/listinfo/cfp-interest


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.oakapple.net/pipermail/cfp-interest/attachments/20230131/a5d5be97/attachment.htm>