See Section 5.9.5 of MPI-3 or the section named "User-Defined Reduction Operations" but presumably numbered differently in older copies of the MPI standard.
An older but still relevant online reference is http://www.mpi-forum.org/docs/mpi-2.2/mpi22-report/node107.htm There is a proposal to support __float128 in the MPI standard in the future but it has not been formally considered by the MPI Forum yet [https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/318]. Best, Jeff On Sat, Feb 1, 2014 at 2:28 PM, Tim Prince <n...@aol.com> wrote: > > On 02/01/2014 12:42 PM, Patrick Boehl wrote: >> >> Hi all, >> >> I have a question on datatypes in openmpi: >> >> Is there an (easy?) way to use __float128 variables with openmpi? >> >> Specifically, functions like >> >> MPI_Allreduce >> >> seem to give weird results with __float128. >> >> Essentially all I found was >> >> http://beige.ucs.indiana.edu/I590/node100.html >> >> where they state >> ---- >> MPI_LONG_DOUBLE >> This is a quadruple precision, 128-bit long floating point number. >> ---- >> >> But as far as I have seen, MPI_LONG_DOUBLE is only used for long doubles. >> >> The Open MPI Version is 1.6.3 and gcc is 4.7.3 on a x86_64 machine. >> > It seems unlikely that 10 year old course notes on an unspecified MPI > implementation (hinted to be IBM power3) would deal with specific details of > openmpi on a different architecture. > Where openmpi refers to "portable C types" I would take long double to be > the 80-bit hardware format you would have in a standard build of gcc for > x86_64. You should be able to gain some insight by examining your openmpi > build logs to see if it builds for both __float80 and __float128 (or > neither). gfortran has a 128-bit data type (software floating point > real(16), corresponding to __float128); you should be able to see in the > build logs whether that data type was used. > > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users -- Jeff Hammond jeff.scie...@gmail.com
