[mpich-devel] MPI_Pack/MPI_Unpack/MPI_Pack_size and large datatypes

[Jeff Hammond]

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

But seriously, does anyone use Pack functions?

Jeff

----- Original Message -----
> From: "Rob Latham" <robl at mcs.anl.gov>
> To: devel at mpich.org
> 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:
> > 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
> 

-- 
Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381
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