[mpiwg-p2p] FP16 Support

[Gropp, William D]

Note that IEEE754 is about to expire - all IEEE standards, as I understand it, must be renewed on a regular schedule. Someone, say a major processor vendor, might want to speak up for it :)
Bill

Sent from my iPad

> On Jun 22, 2017, at 7:40 AM, Jeff Hammond <jeff.science at gmail.com> wrote:
> 
> I would like to move beyond languages here and have MPI define IEEE754 types. So we'd have e.g. MPI_IEEE32BIT for single, etc.
> 
> MPI would do the math according to IEEE in whatever language the implementation uses. Languages would need to have a compatible type to allow the user to manipulate the resulting buffers.
> 
> Jeff  
> 
> Sent from my iPhone
> 
>> On Jun 21, 2017, at 10:24 PM, Atsushi HORI <ahori at riken.jp> wrote:
>> 
>> Hello, Bill,
>> 
>>> 2017/06/22 14:03、William Gropp <wgropp at illinois.edu> wrote;
>>> 
>>> On timing, note that MPI already defined optional types.  One of these is MPI_REAL2, which is a 2-byte floating point type - that is, FP16. (See p25, line 36, 177, line 2, 540 line 10, and 674 line 38).  Was MPI_REAL2 discussed?
>> 
>> I did not notice of that and there was no discussion about MPI_REAL2 (unless I missed).
>> 
>> I checked 3.1 standard as you pointed out, but MPI_REAL2 is defined as a Fortran type. I believe that there is no C predefined type for FP16 (or 'MPI_HALF') in MPI 3.1. This is just because ISO C does not define FP16 yet. 
>> 
>> 
>> — from p25, MPI 3.1,
>> MPI requires support of these datatypes, which match the basic datatypes of Fortran and ISO C. Additional MPI datatypes should be provided if the host language has additional data types: MPI_DOUBLE_COMPLEX for double precision complex in Fortran declared to be of type DOUBLE COMPLEX; MPI_REAL2, MPI_REAL4, and MPI_REAL8 for Fortran reals, declared to be of type REAL*2, REAL*4 and REAL*8, respectively; MPI_INTEGER1, MPI_INTEGER2, and MPI_INTEGER4 for Fortran integers, declared to be of type INTEGER*1, INTEGER*2, and INTEGER*4, respectively; etc.
>> 
>> -----
>> Atsushi HORI
>> ahori at riken.jp
>> http://aics-sys.riken.jp
>> 
>> 
>> 
>> 
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