[Mpi3-rma] Target displacement sign issue

[Jim Dinan]

Hi All,

Here is the suggested change to address this issue.  In the paragraph on 
page 425, line 1, add the bracketed sentence:

In the case of a window created with MPI_WIN_CREATE_DYNAMIC, the 
target_disp for all RMA functions is the address at the target; i.e., 
the effective window_base is MPI_BOTTOM and the disp_unit is one. [Thus, 
for dynamic windows, the target_disp argument to all RMA functions in 
interpreted as unsigned.] Users should use MPI_GET_ADDRESS at the target 
process to determine the address of a target memory location and 
communicate this address to the origin process.

   ~Jim.

On 8/28/12 9:46 AM, Jim Dinan wrote:
> 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.