From: jpprost@XXXXXXXXXX
X-Lotus-FromDomain: IBMUS
To: Hubert Ritzdorf <ritzdorf@XXXXXXXXXXXXXXXXXXXXXXXXXXX>
cc: mpi-core@XXXXXXXXXXX
Date: Tue, 2 Feb 1999 10:59:34 -0500
Subject: Re: Question to MPI/IO
Sender: owner-mpi-core@XXXXXXXXXXX

Hubert,

Version (i) is the version intended by the standard, which says:
"The function must begin copying at the location in userbuf specified by
position
into the (tiled) datatype."
Note that your note was confusing, because the descriptions of the two
alternatives before
the code and within the code are opposite. The right description is the one
given
within the code. Instead of saying "the user must find...", I would rather
say "the user defined
conversion routine must determine..."
Jean-Pierre

###################################################
Jean-Pierre Prost
IBM T.J. Watson Research Center
PO Box 218
Yorktown Heights, NY 10598
USA
Phone: (914) 945 3225
Fax: (914) 945 2141
Internet: jpprost@XXXXXXXXXX
Lotus Notes: Jean-Pierre Prost/Watson/IBM @ IBMUS
VM: IBMUSM11(JPPROST)
Home page: http://www.research.ibm.com/people/p/prost/
###################################################



Hubert Ritzdorf <ritzdorf@XXXXXXXXXXXXXXXXXXXXXXXXXXX> on 02/02/99 05:52:05
To:   mpi-core@XXXXXXXXXXX
cc:    (bcc: Jean-Pierre Prost/Watson/IBM)
Subject:  Question to MPI/IO






Hi,

I am implementing MPI for NEC SX computers and I have a question to
Datarep Conversion functions (chapter 9.5.3 of the MPI-2 document)

(*)  If MPI cannot allocate a (file) buffer large enough to hold all the
     the data to be converted, the standard says:

     For the first call, MPI will call the (conversion) function with
     ``position'' set to zero. ...
     Then in subsequent calls to the conversion function,
     MPI will increment the value in ``position'' by the ``count''
     of items converted in the previous call.

     My question is:
     Is the user buffer ``buf'' incremented correspondingly
     in the second call (and further calls) of the conversion function
     (cf. Version i below) or
     must the user find the correct position in the user buffer ``buf''
     within the conversion function (cf. Version ii below)?

     i.e.

        /* first call */
           position = 0;
           write_fn (buf, datatype, count, filebuf, position, extra_state);

        /* write filebuf to the file */

           write (.., filebuf, count*datarep_size);



        /* (Version i)
            second call, the user must find the correct position in buf */

           position = count;
           write_fn (buf, datatype, count, filebuf, position, extra_state);


     or

        /* (Version ii)
           second call, MPI transfers the new user buffer location */

           position = count;
           next_buf = (char *) buf + count * native_size;
           write_fn (next_buf, datatype, count, filebuf, position,
extra_state);
        /* write filebuf to the file */

           write (.., filebuf, count*datarep_size);



  Best regards

  Hubert



___________________________________________________________________________
___

   Hubert Ritzdorf

   NEC Europe Ltd.
   C&C Research Laboratories
   Rathausallee 10
   D-53757 Sankt Augustin

   Tel.: +49 (0) 2241 / 92 52 65
   Fax : +49 (0) 2241 / 92 52 99
   e-mail  : ritzdorf@ccrl-nece.technopark.gmd.de
   InPerson: ritzdorf@XXXXXXXXXXXXXX or
             ritzdorf@XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
   WWW     : http://www.ccrl-nece.technopark.gmd.de/~ritzdorf
___________________________________________________________________________
___