Hello Jeff, thank you a lot for your reply!
On 01.02.2014, at 23:07, Jeff Hammond wrote: > 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 > In this example they construct this "datatype" --------- typedef struct { double real,imag; } Complex --------- and later --------- MPI_Datatype ctype; /* explain to MPI how type Complex is defined */ MPI_Type_contiguous(2, MPI_DOUBLE, &ctype); --------- Do I understand correctly that I have to find out how __float128 is constructed internally and convert it to a form which is compatible with the standard MPI Datatypes? In an analogue way as they do in the example. Up to now, I only found out that __float128 should be somehow the sum of two doubles. Again, I am grateful for any help! Best regards, Patrick > 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 > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users
