I liked Mark's suggestion. Using MPI_Count rather than explicitly fixing the size means the user has to check for overflow. Did the person state what the portability issues with int64_t could be? Is there a C "basic type" that would be compatible with a fortran INTEGER*8? BTW, we already added stdint datatypes to MPI 2.2. -d On 01/25/2010 03:04 PM, Jeff Squyres wrote:

On Jan 24, 2010, at 9:21 PM, Snir, Marc wrote:

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I would suggest to use explicitly 64 bit integers as the type of count in the new functions. I.e., int64_t in C and INTEGER(KIND=8) in Fortran. Both types are part of the (C/Fortran) standard.

FWIW, I mentioned the above point on the MPI3 Fortran WG mailing list and got this reply:

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Please do not touch any of the<stdint.h> stuff with a bargepole! Stick to the basic types and MPI type names.

There are many different ways where<stdint.h> integers cause portability, efficiency and other problems. Inter alia, the current revision of C is thinking of changing them in ways that could be incompatible with old code, and they are semantically incompatible with Fortran and many other languages in several respects.

MPI_count gives the opportunity to evade any such chaos, whether introduced by the standard or an implementation.