[Mpi3-rma] Target displacement sign issue

[Jim Dinan]

Hi All,

Currently, target displacements in put/get/acc/etc are defined to be 
non-negative integers of type, MPI_Aint.  MPI_Aint is defined to be a 
signed integer.  However, displacements associated with dynamic windows 
are addresses (unsigned) and can range into the space of negative integers.

It seems like the least impact change would be to add a special case 
that the displacement argument will be interpreted as unsigned for 
dynamic windows.  Changing the interface to take an 'unsigned MPI_Aint' 
would be the most clear (and preserve the existing and intended new 
semantics), but would break backward compatibility.

Interested to hear your thoughts.

  ~Jim.