On Fri, Oct 18, 2013 at 08:17:56PM -0500, Jeff Hammond wrote:

Let's just deprecate Pack functions instead of fixing them. That's what we did for C++ :-)

But seriously, does anyone use Pack functions?

They are the most straightforward way to deal with datatypes. parallel-netcdf uses pack/unpack . ==rob

Jeff

----- Original Message -----

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From: "Rob Latham" <[email protected]> To: [email protected] Sent: Friday, October 18, 2013 8:15:42 PM Subject: Re: [mpich-devel] MPI_Pack/MPI_Unpack/MPI_Pack_size and large datatypes

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

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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

-- Rob Latham Mathematics and Computer Science Division Argonne National Lab, IL USA