X-Mailer: exmh version 2.0.2 2/24/98
To: mpi-core@XXXXXXXXXXX
Subject: Question to MPI/IO
Date: Tue, 02 Feb 1999 11:52:05 +0100
From: Hubert Ritzdorf <ritzdorf@XXXXXXXXXXXXXXXXXXXXXXXXXXX>
Sender: owner-mpi-core@XXXXXXXXXXX


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
______________________________________________________________________________