[Mpi3-bwcompat] MPI Backward Compatibility Working Group

[Rajeev Thakur]

What was the motivation for the new MPI_Type_get_extent_x and MPI_Type_get_true_extent_x functions?

If we say MPI_Count should be at least as large as MPI_Aint, why can't we just use MPI_Aint instead? The data buffer can't be larger than Aint size. I know that for I/O MPI_Offset can be larger than Aint, but this proposal does not solve the I/O problem as far as I know.

https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/265

Rajeev

On Mar 11, 2011, at 5:06 PM, Solt, David George wrote:

> During our meeting today we decided that MPI_Count should be at least as large as an MPI_Aint.    We already had the restriction that it had to be as large as a C/Fortran integer.   We want both restrictions (they cannot be combined because there is no guarantee that MPI_Aint > integer).
>  
> I’ll throw this out as a starting point for discussion:
>  
>  
>  
>  
> 2.5.8 Last sentence change to:
>  
> The size of the MPI_Count type is determined by the MPI implementation
> with the restriction that it must be minimally capable of encoding a C int and Fortran INTEGER
> and any value that may be stored in an MPI_Aint type.
>  
> Rational thingy:
>  
> MPI_Count is used to communicate both the number of elements in a datatype and the bounds of a datatype.
> The number of elements in a datatype is specified at creation time using a C int or Fortran INTEGER.   The bounds
> may be specified using an MPI_Aint. 
>  
>  
> So, I was especially brief here.   I did not want to get into the “new” routines vs. “old routines”, but if you attempt to go into more depth than what I said, you will inevitably end up going down that path.  I can think of a thousand ways not to say it, but its hard to come up with a good way.
> Dave  
>  
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