On Jun 16, 2017, at 7:19 PM, Rolf Rabenseifner <[email protected]> wrote:

Jeff is partially right: If the Fortran user uses selected_real_kind(p, r), then all is done.

On the other hand, I expect that the Fortran standardization body will do the same as the C standardization body, namely to add a new language Basic type.

No. The basic type is REAL. This is just another KIND of REAL. This is not much of an issue for the standard. It is a HUGE deal for implementations. Cheers, Bill

For this of course, we have to provide the corresponding MPI predefined datatype. Rolf

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From: "Jeff Hammond" <[email protected]> To: "MPI WG Point To Point Communications working group" <[email protected]> Cc: "Atsushi Hori" <[email protected]>, "Reinhold Bader" <[email protected]>, "fortran standards email list for J3" <[email protected]>, "MPI-WG Fortran working group" <[email protected]> Sent: Friday, June 16, 2017 5:11:24 PM Subject: Re: [MPIWG Fortran] [mpiwg-p2p] FP16 16-bit-floating-point

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No change to the MPI standard is required here. MPI_Type_create_f90_real is already sufficient.

"This function returns a predefined MPI datatype that matches a REAL variable of KIND selected_real_kind(p, r)." - I do not see why we need to enumerate a predefined datatype name associated with float16 in Fortran for this statement to be true. An implementation can return a datatype with the appropriate properties without being enumerated like MPI_REAL.

"It is erroneous to supply values for p and r not supported by the compiler." - Conversely, the user should be allowed to supply values that are supported by the compiler (although the standard doesn't guarentee it today). MPI implementations might not support every type the compiler does, as is already the case for Fortran float128 (because MPI libraries are written in C, and do not call back into Fortran to do math on these types, which may not be identical to C extensions like __float128), but I consider that an implementation defect.

Thus, I propose to merely add the text that allows users to rely on MPI_Type_create_f90_real for float16 in Fortran, provided that the compiler supports it. It will then be up to implementations to figure out how to do math on these types internally.

While we are on this subject, we should be considering the more general inadequacy of the current state of the MPI type system from the perspective of reductions. See [ https://github.com/mpi-forum/mpi-issues/issues/18 | https://github.com/mpi-forum/mpi-issues/issues/18 ] for details.

As for ISO C/C++, I can talk to Clark Nelson if a better candidate is not identified, but Lawrence Crowl is leading the C++ effort and I suspect the C folks will follow, although I will confirm this with Clark.

Jeff

On Fri, Jun 16, 2017 at 6:16 AM, Kawashima, Takahiro < [ mailto:[email protected] | [email protected] ] > wrote:

Hi,

I don't know the status of C standardization nor contact person but the suggestion of 'short float' was seem to made in a WG.

[ http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0192r0.pdf | http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0192r0.pdf ] [ http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2016.pdf | http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2016.pdf ]

Regards, Takahiro Kawashima, Fujitsu

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Tony,

we try to find the type names used in C and Fortran before we define the new predefined MPI datatype handles for representing those language types.

Who knows, whom we can contact on the C standardization side?

Best regards Rolf

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From: "Anthony Skjellum" < [ mailto:[email protected] | [email protected] ] > To: "MPI WG Point To Point Communications working group" < [ mailto:[email protected] | [email protected] ] > Cc: "Reinhold Bader" < [ mailto:[email protected] | [email protected] ] >, "Atsushi Hori" < [ mailto:[email protected] | [email protected] ] >, "fortran standards email list for J3" < [ mailto:[email protected] | [email protected] ] >, "MPI-WG Fortran working group" < [ mailto:[email protected] | [email protected] ] > Sent: Friday, June 16, 2017 2:50:00 PM Subject: Re: [MPIWG Fortran] [mpiwg-p2p] FP16 16-bit-floating-point

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Rolf, apart from the Fortan angle, may I strongly encourage that we adopt this datatype for MPI-4. It is part of real MPI codes already, but now we have to fake transfer datatypes as 16-bit integers or bytes... which means not really right if heterogeneous interoperability were to be maintained. And this is a canonical IEEE type now, as you note. There is also the "2 half-float" datatype (32-bits) at least in CUDA to be looked at; maybe ignored or maybe supported, but it is there too. Key to this MPI users and applications use half floats and 2 half-floats :-) in practice.

May I also suggest a forward look at the types in AVX-512, in case any of these become particularly relevant in future. At least 8-bit integers are conceptually new, apart from BYTE. [ [ https://en.wikipedia.org/wiki/AVX-512 | https://en.wikipedia.org/wiki/AVX-512 ] | [ https://en.wikipedia.org/wiki/AVX-512 | https://en.wikipedia.org/wiki/AVX-512 ] ]

Regards, Tony

On Fri, Jun 16, 2017 at 6:52 AM, Rolf Rabenseifner < [ mailto: [ mailto:[email protected] | [email protected] ] | [ mailto:[email protected] | [email protected] ] ] > wrote:

Hi all together,

I'm sitting in the MPI Forum Meeting and we discuss the new IEEE FP16 datatype.

Questions to the Fortran atandardization body:

- Does the Fortran Standardization Body has already a proposal for the new name in Fortran for this IEEE FP16?

- Will be REAL*2 identical to IEEE FP16?

Best regards Rolf

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-- Jeff Hammond [ mailto:[email protected] | [email protected] ] [ http://jeffhammond.github.io/ | http://jeffhammond.github.io/ ]

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