Date: Fri, 8 Oct 2021 09:38:40 -0700
On Fri, Oct 8, 2021 at 9:34 AM David Olsen via Liaison <
liaison_at_[hidden]> wrote:
> Tom:
> > > Thank you, Gaby, but I'm still a little confused. Could you please
> > > elaborate with regard to what runtime semantics you believe would
> > > differ?
>
> Gaby:
> > See the conversion/promotion rules - I think they were points 2, 3, and
> 4 on the slide presentations.
>
> The only runtime difference between the two languages that P1467 would
> have introduced was a very slight difference in usual arithmetic
> conversions. After the discussion and polls in the SG22/CFP meeting, I
> will tweak the usual arithmetic conversion rules in P1467 to match the C23
> rules. With that change to P1467, there won't be any places left where the
> C and C++ standards require different runtime behavior in the area of
> extended floating-point.
>
Can you make sure that this change is explained in the paper, to make sure
EWG / LEWG don't have objections?
> There will still be a difference in compile-time behavior, in the area of
> whether or not certain conversions are implicit. That only affects compile
> time. If the code compiles in both languages, it will behave the same in
> both languages.
>
>
>
> -----Original Message-----
> From: Liaison <liaison-bounces_at_[hidden]> On Behalf Of Gabriel Dos
> Reis via Liaison
> Sent: Thursday, October 7, 2021 9:32 AM
> To: Tom Honermann <tom_at_[hidden]>; Aaron Ballman <
> aaron_at_[hidden]>; WG14/WG21 liaison mailing list <
> liaison_at_[hidden]>
> Cc: Gabriel Dos Reis <gdr_at_[hidden]>
> Subject: Re: [wg14/wg21 liaison] C and C++ Compatibility SG meeting
> summary for Oct 06, 2021
>
>
> [Tom]
> > Thank you, Gaby, but I'm still a little confused. Could you please
> > elaborate with regard to what runtime semantics you believe would
> > differ?
>
> See the conversion/promotion rules - I think they were points 2, 3, and 4
> on the slide presentations.
>
> > What changes would be needed to align the runtime semantics across the
> languages?
>
> The rules that the WG14 representatives were unwilling to make. See the
> poll results.
>
> Note: I am quite happy with the C++ proposal, EXCEPT the aliasing part.
> I would reconsider my vote and recommendations to the various constituents
> when there is sufficient convergence. I would still recommend against the
> _Fxxx names in the global namespace.
>
> -- Gaby
>
> -----Original Message-----
> From: Tom Honermann <tom_at_[hidden]>
> Sent: Thursday, October 7, 2021 9:25 AM
> To: Gabriel Dos Reis <gdr_at_[hidden]>; Aaron Ballman <
> aaron_at_[hidden]>; WG14/WG21 liaison mailing list <
> liaison_at_[hidden]>
> Subject: Re: [wg14/wg21 liaison] C and C++ Compatibility SG meeting
> summary for Oct 06, 2021
>
> On 10/7/21 12:19 PM, Gabriel Dos Reis wrote:
> > The polls that were taken before this one indicated that both languages
> are headed towards distinct types that behave similarly in certain ways,
> but distinctly in other ways, and yet it was repeated that the goal was
> that if a program using those types compiles in both C and C++, then the
> runtime semantics should be the same. And that wasn't happening.
> Consequently, pretending that the types in C++ were aliases to the types in
> C was just plain misleading and wrong. If we are concerned about economic
> harms because of differences, there subtle differences should dissuade us
> to purse an "type aliasing" semantics.
>
> Thank you, Gaby, but I'm still a little confused. Could you please
> elaborate with regard to what runtime semantics you believe would differ?
> What changes would be needed to align the runtime semantics across the
> languages?
>
> Tom.
>
> >
> > -- Gaby
> >
> > -----Original Message-----
> > From: Aaron Ballman <aaron_at_[hidden]>
> > Sent: Thursday, October 7, 2021 8:55 AM
> > To: WG14/WG21 liaison mailing list <liaison_at_[hidden]>
> > Cc: Tom Honermann <tom_at_[hidden]>
> > Subject: Re: [wg14/wg21 liaison] C and C++ Compatibility SG meeting
> > summary for Oct 06, 2021
> >
> > On Thu, Oct 7, 2021 at 11:39 AM Tom Honermann via Liaison
> > <liaison_at_[hidden]> wrote:
> >> Thank you for hosting the meeting yesterday, Aaron!
> > My pleasure, I'm glad it was a productive meeting, thank you for
> participating!
> >
> >> With regard to this poll: Should the _Float* C names be available
> >> (through some means) in C++ and be used as the types behind the
> >> std::float* aliases?
> >>
> >> The SA vote rationale was "My reasons against were that similar but
> >> slightly incompatible types is not good for the same names. ...."
> >>
> >> Previous polls had consensus to align the usual arithmetic
> >> conversions between C and C++, but did not have consensus for
> >> applying the C++ implicit conversion rules to C. With regard to the
> >> SA rationale above, is the "slightly incompatible types" concern
> >> directed at those differences in the implicit conversion rules? Or is
> >> the concern over other differences? If the latter, a list of notable
> >> differences would be useful.
> > I'll leave it to the person who made the comments to explain further,
> > but my personal interpretation of the comment was that there was
> > unease with exposing the C names in C++ unless the semantics were
> > identical and there are cases where the semantics are compatible for a
> > well-formed program in both languages but not identical across
> > languages. If I have this wrong, hopefully I'll be corrected.
> >
> >> My understanding is that the intent of P1467R4, and as stated by the
> >> author yesterday, is that these types would have the same semantics
> >> in each language with the only exception being that, in some cases, a
> >> use may be ill-formed in one language and not the other (e.g., the
> >> differences in the implicit conversion rules).
> > This matches my understanding of the authors' intent with P1467.
> >
> > ~Aaron
> >
> >> Tom.
> >>
> >> On 10/7/21 8:57 AM, Aaron Ballman via Liaison wrote:
> >>> The meeting minutes from the Oct 2021 special session on
> >>> floating-point types can be found at:
> >>>
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwiki.edg.com%2Fbin%2Fview%2FWg21telecons2021%2FTeleconference2021-10-06&data=04%7C01%7Cdolsen%40nvidia.com%7Ca3f17acf5c3c4cf8826e08d989affa95%7C43083d15727340c1b7db39efd9ccc17a%7C0%7C0%7C637692211192096937%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=p0fMBjQpNt%2BXVnbwwXtUlWlppMQ6GFLGXHD4A5J0xS8%3D&reserved=0
> .
> >>> The WG14 minutes will be posted to the document log in the near
> >>> future.
> >>>
> >>> Big thanks to Rajan Bhakta for taking minutes, and to all the
> >>> attendees for having such a productive special session!
> >>>
> >>> ~Aaron
>
> _______________________________________________
> Liaison mailing list
> Liaison_at_[hidden]
> Subscription: https://lists.isocpp.org/mailman/listinfo.cgi/liaison
> Link to this post: http://lists.isocpp.org/liaison/2021/10/0884.php
>
liaison_at_[hidden]> wrote:
> Tom:
> > > Thank you, Gaby, but I'm still a little confused. Could you please
> > > elaborate with regard to what runtime semantics you believe would
> > > differ?
>
> Gaby:
> > See the conversion/promotion rules - I think they were points 2, 3, and
> 4 on the slide presentations.
>
> The only runtime difference between the two languages that P1467 would
> have introduced was a very slight difference in usual arithmetic
> conversions. After the discussion and polls in the SG22/CFP meeting, I
> will tweak the usual arithmetic conversion rules in P1467 to match the C23
> rules. With that change to P1467, there won't be any places left where the
> C and C++ standards require different runtime behavior in the area of
> extended floating-point.
>
Can you make sure that this change is explained in the paper, to make sure
EWG / LEWG don't have objections?
> There will still be a difference in compile-time behavior, in the area of
> whether or not certain conversions are implicit. That only affects compile
> time. If the code compiles in both languages, it will behave the same in
> both languages.
>
>
>
> -----Original Message-----
> From: Liaison <liaison-bounces_at_[hidden]> On Behalf Of Gabriel Dos
> Reis via Liaison
> Sent: Thursday, October 7, 2021 9:32 AM
> To: Tom Honermann <tom_at_[hidden]>; Aaron Ballman <
> aaron_at_[hidden]>; WG14/WG21 liaison mailing list <
> liaison_at_[hidden]>
> Cc: Gabriel Dos Reis <gdr_at_[hidden]>
> Subject: Re: [wg14/wg21 liaison] C and C++ Compatibility SG meeting
> summary for Oct 06, 2021
>
>
> [Tom]
> > Thank you, Gaby, but I'm still a little confused. Could you please
> > elaborate with regard to what runtime semantics you believe would
> > differ?
>
> See the conversion/promotion rules - I think they were points 2, 3, and 4
> on the slide presentations.
>
> > What changes would be needed to align the runtime semantics across the
> languages?
>
> The rules that the WG14 representatives were unwilling to make. See the
> poll results.
>
> Note: I am quite happy with the C++ proposal, EXCEPT the aliasing part.
> I would reconsider my vote and recommendations to the various constituents
> when there is sufficient convergence. I would still recommend against the
> _Fxxx names in the global namespace.
>
> -- Gaby
>
> -----Original Message-----
> From: Tom Honermann <tom_at_[hidden]>
> Sent: Thursday, October 7, 2021 9:25 AM
> To: Gabriel Dos Reis <gdr_at_[hidden]>; Aaron Ballman <
> aaron_at_[hidden]>; WG14/WG21 liaison mailing list <
> liaison_at_[hidden]>
> Subject: Re: [wg14/wg21 liaison] C and C++ Compatibility SG meeting
> summary for Oct 06, 2021
>
> On 10/7/21 12:19 PM, Gabriel Dos Reis wrote:
> > The polls that were taken before this one indicated that both languages
> are headed towards distinct types that behave similarly in certain ways,
> but distinctly in other ways, and yet it was repeated that the goal was
> that if a program using those types compiles in both C and C++, then the
> runtime semantics should be the same. And that wasn't happening.
> Consequently, pretending that the types in C++ were aliases to the types in
> C was just plain misleading and wrong. If we are concerned about economic
> harms because of differences, there subtle differences should dissuade us
> to purse an "type aliasing" semantics.
>
> Thank you, Gaby, but I'm still a little confused. Could you please
> elaborate with regard to what runtime semantics you believe would differ?
> What changes would be needed to align the runtime semantics across the
> languages?
>
> Tom.
>
> >
> > -- Gaby
> >
> > -----Original Message-----
> > From: Aaron Ballman <aaron_at_[hidden]>
> > Sent: Thursday, October 7, 2021 8:55 AM
> > To: WG14/WG21 liaison mailing list <liaison_at_[hidden]>
> > Cc: Tom Honermann <tom_at_[hidden]>
> > Subject: Re: [wg14/wg21 liaison] C and C++ Compatibility SG meeting
> > summary for Oct 06, 2021
> >
> > On Thu, Oct 7, 2021 at 11:39 AM Tom Honermann via Liaison
> > <liaison_at_[hidden]> wrote:
> >> Thank you for hosting the meeting yesterday, Aaron!
> > My pleasure, I'm glad it was a productive meeting, thank you for
> participating!
> >
> >> With regard to this poll: Should the _Float* C names be available
> >> (through some means) in C++ and be used as the types behind the
> >> std::float* aliases?
> >>
> >> The SA vote rationale was "My reasons against were that similar but
> >> slightly incompatible types is not good for the same names. ...."
> >>
> >> Previous polls had consensus to align the usual arithmetic
> >> conversions between C and C++, but did not have consensus for
> >> applying the C++ implicit conversion rules to C. With regard to the
> >> SA rationale above, is the "slightly incompatible types" concern
> >> directed at those differences in the implicit conversion rules? Or is
> >> the concern over other differences? If the latter, a list of notable
> >> differences would be useful.
> > I'll leave it to the person who made the comments to explain further,
> > but my personal interpretation of the comment was that there was
> > unease with exposing the C names in C++ unless the semantics were
> > identical and there are cases where the semantics are compatible for a
> > well-formed program in both languages but not identical across
> > languages. If I have this wrong, hopefully I'll be corrected.
> >
> >> My understanding is that the intent of P1467R4, and as stated by the
> >> author yesterday, is that these types would have the same semantics
> >> in each language with the only exception being that, in some cases, a
> >> use may be ill-formed in one language and not the other (e.g., the
> >> differences in the implicit conversion rules).
> > This matches my understanding of the authors' intent with P1467.
> >
> > ~Aaron
> >
> >> Tom.
> >>
> >> On 10/7/21 8:57 AM, Aaron Ballman via Liaison wrote:
> >>> The meeting minutes from the Oct 2021 special session on
> >>> floating-point types can be found at:
> >>>
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwiki.edg.com%2Fbin%2Fview%2FWg21telecons2021%2FTeleconference2021-10-06&data=04%7C01%7Cdolsen%40nvidia.com%7Ca3f17acf5c3c4cf8826e08d989affa95%7C43083d15727340c1b7db39efd9ccc17a%7C0%7C0%7C637692211192096937%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=p0fMBjQpNt%2BXVnbwwXtUlWlppMQ6GFLGXHD4A5J0xS8%3D&reserved=0
> .
> >>> The WG14 minutes will be posted to the document log in the near
> >>> future.
> >>>
> >>> Big thanks to Rajan Bhakta for taking minutes, and to all the
> >>> attendees for having such a productive special session!
> >>>
> >>> ~Aaron
>
> _______________________________________________
> Liaison mailing list
> Liaison_at_[hidden]
> Subscription: https://lists.isocpp.org/mailman/listinfo.cgi/liaison
> Link to this post: http://lists.isocpp.org/liaison/2021/10/0884.php
>
Received on 2021-10-08 11:38:55