[MPI3 Fortran] Straw vote on integers kinds

[Bill Long]

Craig Rasmussen wrote:
> 
> On Sep 15, 2009, at 9:57 AM, Jeff Squyres wrote:
> 
>> On Sep 15, 2009, at 11:40 AM, Craig Rasmussen wrote:
>>
>>> No intent really.  It is just that the interface is not complete yet.
>>> I'm not sure there is a need for real kinds so perhaps MPI_DOUBLE_KIND
>>> should be removed.  Jeff, any place for reals except in MPI users
>>> defined types?
>>>
>>
>> The only C double that is passed in the MPI interface is the return 
>> value from MPI_WTICK and MPI_WTIME.
>>
> 
> So let's get rid of MPI_DOUBLE_KIND.  The compiler will do normal type 
> conversion for return values so we don't really have the same issue we 
> have with procedure arguments.
> 
> But what is the correct way to specify the result value?  I believe 
> DOUBLE PRECISION is frowned upon.  I haven't been on the committee long 
> enough to know the reason.

DOUBLE PRECISION is problematic, since the dreaded -r8 switch may turn 
this into a 128-bit floating point value.  If the C interface explicitly 
says that the return value is 'double', then the Fortran interface 
should declare the return type as REAL(C_DOUBLE).  That's the utility of 
having constants like C_DOUBLE in the iso_c_binding module.

Cheers,
Bill



> 
> -craig
> 
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-- 
Bill Long                                   longb at cray.com
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