(j3.2006) (SC22WG5.3757) Ballot on the technical content of the TR

Robert Corbett Robert.Corbett
Mon Dec 8 21:49:07 EST 2008


Craig Rasmussen wrote:
> 
> On Dec 7, 2008, at 7:46 PM, Jim Xia wrote:
> 
>> 2.) Fortran descriptors 
>> Although Fortran descriptors are used when passing assumed-shape 
>> arrays, pointer 
>> arrays and allocatable arrays by many vendors, they are however not 
>> universally used 
>> by all vendors.  Based on a survey earlier this year (by Craig 
>> Rasmussen at J3 m183), 
>> some vendors haven't adopted descriptors for assumed shape arrays, 
>> pointer arrays 
>> or allocatable arrays.  The requirement in the C-interop TR may pose 
>> implementation 
>> difficulties for those vendors.  Furthermore allowing updates on 
>> Fortran descriptors from 
>> C programs will likely cause safety issues and also be problematic in 
>> consistency 
>> check by some vendors.  This becomes a sure way to introduce bugs 
>> difficult to diagnose. 
> 
> 
> I'm not sure what I said about descriptors at J3 m183 but I certainly 
> didn't intend to give the impression that some vendors don't implement 
> Fortran descriptors.  In fact, EVERY vendor I have been able to test 
> does.  Some vendors don't include the rank as part of the descriptor, 
> though most do.  Perhaps this is what Jim is referring to.
> 
> Regards,
> Craig

Sun Fortran uses decriptors for assumed-shape arrays, but the
descriptors contain only those components required by the
Fortran language.  The structure used as a descriptor for an
assumed-shaped array of rank n has the form:

      actual origin (an address)
      extents (n unsigned longs)
      strides (n signed longs)

I am not pleased that the proposal is making other vendors' extensions
to the data structures, beyond what is needed for Fortran, part of the
Fortran language.

Bob Corbett



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