On Fri, Oct 18, 2013 at 04:44:32PM -0500, Pavan Balaji wrote:

Hi Rob,

I totally agree with adding this into MPICH.

However, with respect to the MPI standard, can one not implement MPIX_Pack_x on top of current MPI-3 using appropriate datatype creation?

It'd have to be "next to" or "inside", but not "on top of". The usual trick of "just describe big type with a smaller number of CONTIGs won't work: MPI_Pack(const void *inbuf, int incount, MPI_Datatype datatype, void * outbuf, int outcount int *position); We're ok on inputs: a normal buf, count, datatype tuple. How do you work around the output, though? outcount is a count of bytes, not a count of datatypes. Position is a plain old pointer to memory. ==rob -- Rob Latham Mathematics and Computer Science Division Argonne National Lab, IL USA