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