[Mpi-forum] MPI_Type_size question

[Fab Tillier]

Rob Ross wrote on Fri, 18 Jun 2010 at 13:13:26

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

Oops, you're right, I'm off by 1024 from what I had entended, the count should have been: 1073741824

Sorry!
-Fab

> 
> 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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