Hi, I'm afraid that the proposed straw vote mixes up two things: 1) The need to handle 64-bit integers (say, if the user says -i8) 2) The need to handle 64-bit count arguments (which may be necessary even if other ints are 32-bit) For purpose 1), it looks like option 4) - default integers - are the best way, as Aleks said, whatever happens under the hood. For purpose 2), I'm voting for option 1). Note however that this is actually a part of another discussion that we should wait the Forum decision upon, and offer our opinion on the most appropriate Fortran interface. Best regards. Alexander -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Craig Rasmussen Sent: Thursday, September 18, 2008 10:42 PM To: [email protected]; MPI-3 Fortran working group Subject: Re: [MPI3 Fortran] Argument data sizes On Sep 18, 2008, at 9:15 AM, Bill Long wrote:

Jeff Squyres wrote:

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On Sep 18, 2008, at 9:36 AM, Iain Bason wrote:

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So it isn't that we need the count to be able to convey a huge number, it's that the absence of an interface that accepts an 8 byte count makes it more difficult to write portable programs.

Yes, I understand that, but if MPI itself doesn't accept counts (and other parameter values) larger than what can be represented by a C int, what does allowing an INTEGER*8 in the MPI Fortran interface mean?

But essentially all modern processors use 64-bit addressing. If a C int is 32 bits, then this restriction is a basic design flaw in MPI that needs to be fixed. Either that or a C int needs to be 64 bits. (The earlier discussion about default64 switches originated with legacy supercomputers where, indeed, the default integer in Fortran AND C int were 64 bits, so there was no internal inconsistency.) Getting MPI to force a change on the C standard is probably out of scope. However, fixing the MPI spec to mandate that count arguments be of type int64_t, or perhaps better, intptr_t, is quite reasonable, and recognizes modern reality.

Jeff and I had a talk about several of the issues on the table and I've agreed to summarize. I'll do this by responding to the various threads directly. Bill raises an excellent point regarding the size of something that essentially reflects the amount of memory on a machine. However, this is not in the scope of this group. So any discussion regarding this should be taken up with the wider forum who is considering this topic. However, it is within our purview to discuss how to best represent this size in Fortran. I'm going to take a straw poll on this matter. Please choose one of the following choices: 1. A constant kind value defined by the implementation, e.g., MPI_SIZE_KIND, integer(MPI_SIZE_KIND) :: count It is expected that MPI_SIZE_KIND be the same kind as a default integer 2. Similar to 1. expect the kind value is C_INT 3. Use overloading to select use either (effectively) a C int or a C long. I don't think this will work with default integer dummies 4. Use default integer, write the wrapper in Fortran, and use assignment to cast the integer to C_INT. I vote #1 as it provides the most flexibility to the implementer and the compiler will give an error if the programmer does something stupid. Cheers, Craig _______________________________________________ mpi3-fortran mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-fortran --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies.