NAME

       MPI_Fetch_and_op - Combines the contents of the origin buffer with that of a target buffer
       and returns the target buffer value.

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Fetch_and_op(const void *origin_addr, void *result_addr,
            MPI_Datatype datatype, int target_rank, MPI_Aint target_disp,
            MPI_Op op, MPI_Win win)

Fortran Syntax (see FORTRAN 77 NOTES)

       INCLUDE 'mpif.h'
       MPI_FETCH_AND_OP(ORIGIN_ADDR, RESULT_ADDR, DATATYPE, TARGET_RANK,
                        TARGET_DISP, OP, WIN, IERROR)
            <type> ORIGIN_ADDR, RESULT_ADDR(*)
            INTEGER(KIND=MPI_ADDRESS_KIND) TARGET_DISP
            INTEGER DATATYPE, TARGET_RANK, OP, WIN, IERROR

INPUT PARAMETERS

       origin_addr
                 Initial address of buffer (choice).

       result_addr
                 Initial address of result buffer (choice).

       datatype  Data type of the entry in origin, result, and target buffers (handle).

       target_rank
                 Rank of target (nonnegative integer).

       target_disp
                 Displacement from start of window to beginning  of  target  buffer  (nonnegative
                 integer).

       op        Reduce operation (handle).

       win       Window object (handle).

OUTPUT PARAMETER

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       Accumulate one element of type datatype from the origin buffer (origin_addr) to the buffer
       at offset target_disp, in the target window specified by target_rank and  win,  using  the
       operation op and return in the result buffer result_addr the contents of the target buffer
       before the accumulation.

       The origin and result buffers (origin_addr and result_addr) must be disjoint. Any  of  the
       predefined  operations  for  MPI_Rreduce,  as  well  as  MPI_NO_OP  or MPI_REPLACE, can be
       specified as op; user-defined functions cannot be used. The datatype argument  must  be  a
       predefined datatype. The operation is executed atomically.

       A  new  predefined  operation,  MPI_REPLACE, is defined. It corresponds to the associative
       function f(a, b) =b; that is, the current value in the target memory is  replaced  by  the
       value supplied by the origin.

       A  new  predefined  operation,  MPI_NO_OP,  is  defined. It corresponds to the assiciative
       function f(a, b) = a; that is the current value in the target memory is  returned  in  the
       result buffer at the origin and no operation is performed on the target buffer.

FORTRAN 77 NOTES

       The  MPI standard prescribes portable Fortran syntax for the TARGET_DISP argument only for
       Fortran 90.  FORTRAN 77 users may use the non-portable syntax

            INTEGER*MPI_ADDRESS_KIND TARGET_DISP

       where MPI_ADDRESS_KIND is a constant defined  in  mpif.h  and  gives  the  length  of  the
       declared integer in bytes.

NOTES

       It  is  the  user's responsibility to guarantee that, when using the accumulate functions,
       the target displacement argument is such that accesses to the window are properly  aligned
       according to the data type arguments in the call to the MPI_Fetch_and_op function.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran routines in the last argument.

       Before the error value is returned, the current MPI error handler is called.  By  default,
       this  error  handler aborts the MPI job, except for I/O function errors. The error handler
       may   be   changed   with   MPI_Comm_set_errhandler;   the   predefined   error    handler
       MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not
       guarantee that an MPI program can continue past an error.

SEE ALSO

       MPI_Get_accumulate
       MPI_Reduce