[MPI3 Fortran] Teleconference Wednesday, Sept. 17: Summary

[Bill Long]

Jeff Squyres wrote:
> On Sep 17, 2008, at 12:23 PM, Supalov, Alexander wrote:
>
>> PS. I would not say that there's resistance to the long counts. There's
>> just a number of ways how they can be introduced, and some interesting
>> implications in the file I/O and other areas that may not meet the eye
>> right away.
>>
>> The matter of ILP64 support (i.e., ints as big as longs and pointers)
>> may be rather pertinent. Some guys have old Cray style apps that they
>> want to port. The MPI interface should behave nicely here, I'd say, if
>> only out of respect.
>>
>> Another interesting aspect is the autodouble options, as some call it. I
>> believe this makes all reals be real*8. Again, some people use this,
>> mostly for the same reason, and Fortran MPI interface should probably do
>> something about this now, when we have the chance to do things "right",
>> for a change. :)
>
> Agree with all of the above.
>
> Suffice it to say, the issue is still open for the MPI-3 forum and is 
> not expected to be closed/decided for a while (if for no other reason 
> than MPI-2.2 discussions are likely to take precedence over MPI-3 
> discussions).  So it's good to keep this as an "open item" here in the 
> Fortran WG, but make sure we track what's happening in the overall 
> forum with regards to this issue.
>

For what it's worth, Fortran compilers already have to deal with the 
interaction of modules and default=64 switches.  For example, the 
intrinsic iso_fortran_env module contains named constants 
(numeric_storage_size, for example) that have different values depending 
on these compiler switches.  At least in our case, we have separate 
modules that are stored in library subdirectories with names like 
'default64'. The compiler driver knows which place to look depending on 
the command line options.  This works for "known" modules that are 
supplied along with the compiler (as opposed to user created modules).  
Clearly it is possible to make the MPI module(s) known in this sense.  
(In fact, we do this for MPI already on our systems.)

Cheers,
Bill




-- 
Bill Long                                   longb at cray.com
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