PETSc-FUN3D Code

[Satish Balay]

On Mon, 22 Oct 2007, Lisandro Dalcin wrote:

> Did you take into accout that MPI defines MPI_Aint for this? I believe
> we can reuse that definition, perhaps typedefing it as PetscAint or
> PetscAInt,
> 
> What do you think?

MPI datatypes are c-only - hence not useful for us. For eg: MPI_Comm,
MPI_Aint are C datatypes. The equivalent on the fortran side are
integers. [I guess - the standard wanted to use only the available
native F77 datatypes].

This usually means there could be a mismatch between fortran & c
datatypes. [For eg: on 64bit machines, MPI_Aint is 64bit - whereas
fortran 'integer' is 32bit]. To handle this mismatch - conversion is
usually necessary between these types in the fortran interface
routines [using MPI_Fint as an equvalent for fortran integer] for eg:

         MPI_Fint fcomm   = MPI_Comm_c2f(MPI_Comm comm);
         MPI_Fint foffset = (MPI_Fint)(MPI_Aint offset);
         [i.e int         = (int)(long) => possible truncation]

However we try to keep the fortan and C datatypes similar - so that
such conversions are not necessary. [and we don't have to deal will
errors associated with them]

Satish