[Mpi-forum] MPI_Type_size question

[Rob Ross]

Hi,

Your type isn't big enough to cause overflow. But yes it's an issue.

Rob

On Jun 18, 2010, at 11:55 AM, Fab Tillier wrote:

> Hi Folks,
>
> Looking at putting together the MPI_Count ticket, I ran across the  
> following issue and was hoping to get some guidance.  Take the  
> following code, using the current int counts, and assume sizeof(int)  
> == 4, sizeof(MPI_DOUBLE) == 8:
>
> {
>    MPI_Datatype myType;
>    MPI_Type_contiguous( 1048576, MPI_DOUBLE, &myType );
>
>    int size;
>    MPI_Type_size( myType, &size );
> }
>
> Should MPI_Type_size return an error, due to overflow?  Does size  
> get set to MPI_UNDEFINED and the call succeeds?
>
> Similar issues exist for MPI_Pack with the outsize and position  
> parameters, MPI_Unpack with the insize and position parameters, and  
> MPI_Pack_size with the size parameter.
>
> Lastly, it is my belief that these parameters should really be of  
> type MPI_Aint, but changing this would break backward  
> compatibility.  They cannot be of type MPI_Count, since overflow can  
> occur if MPI_Count is defined as a C int.  How should the standard  
> handle this?
>
> Thoughts?
> -Fab
>
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