How to build MPI libraries for 64-bit integers

Before you continue please verify whether you really need 64-bit integers. It is extra work and perhaps not needed.

We are currently aware of two MPI distributions that can either be installed as 64-bit integer MPI version or offer a pre-installed 64-bit integer configuration:

• Intel MPI (4.0.1 and higher)
• Open MPI (please check below for more details)

Open MPI with 64-bit integers

Please check the integer type of your currently available Open MPI installation (perhaps it can do 64-bit integers already).

For this, type:

ompi_info -a | grep 'Fort integer size'

if the output is:

Fort integer size: 8

then you have a suitable 64-bit Open MPI installation which uses 64-bit integers by default.

If not and you decided that you want to build one yourself (not difficult), then download the latest stable source from http://www.open-mpi.org/ and extract it.

Then enter the directory and configure Open MPI (edit prefix path).

For Intel compilers use:

export F77=ifort
export FC=ifort
export CC=icc
export CXX=icpc
export FFLAGS=-i8
export FCFLAGS=-i8
./configure --prefix=/path/to/openmpi

For GNU compilers use:

export F77=gfortran
export FC=gfortran
export CC=gcc
export CXX=g++
export FFLAGS="-m64 -fdefault-integer-8"
export FCFLAGS="-m64 -fdefault-integer-8"
export CFLAGS=-m64
export CXXFLAGS=-m64
./configure --prefix=/path/to/openmpi

Once the configure step is finished (lot of output, at the end there should be no error), build the library:

make all install

Finally export the path locations (adapt paths) in .bashrc (or in the corresponding file if you don’t use bash):

export PATH=$PATH':/path/to/openmpi/intel/bin'
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH':/path/to/openmpi/intel/lib'

and verify the integer type:

ompi_info -a | grep 'Fort integer size'

if the output is:

Fort integer size: 8

Then you are set. If it is different, then something went wrong. Please double-check and consult Open MPI documentation.