Incosistend integer types in api

[rabauke]

For historical reasons MPI uses int, MPI_Aint, MPI_Offset, and MPI_Count, which may have different ranges and signedness. Integer usage should be harmonized for MPL:

• size_t and ssize_t (when negative values are permissible) should be the only integer types.
• It must be checked for narrowing when passing integer values to underlying MPI library functions.

Edit: MPI 4.0 will introduce large-count support via new functions, see https://eurompi.github.io/assets/papers/2020-09-eurompi2020-mpi4.pdf

[VictorEijkhout]

MPI 4 is going to unify int and MPI_Count. I assume you follow the discussion?

[rabauke]

@VictorEijkhout I am not following the discussion in detail. Thanks, for drawing my attention to these newer developments. Apparently, there are "a few" new MPI functions on the way.