mp_prod_l Subroutine

      SUBROUTINE mp_prod_l (msg, gid)
      !! Multiplies a set of numbers scattered across a number of processes,
      !! then replicates the result.
      !!
      !! MPI mapping
      !! mpi_allreduce

         INTEGER(KIND=int_8), INTENT(INOUT)                 :: msg
         !! a number to multiply (input) and result (output)
         TYPE(mp_comm_type), INTENT(IN)                      :: gid
         !! message passing environment identifier

         CHARACTER(LEN=*), PARAMETER :: routineN = 'mp_sum_l'

         INTEGER                                  :: handle, ierr, msglen

         ierr = 0
         CALL timeset(routineN, handle)

         msglen = 1
#if defined(__parallel)
         CALL mpi_allreduce(MPI_IN_PLACE, msg, msglen, MPI_INTEGER8, MPI_PROD, gid%handle, ierr)
         IF (ierr /= 0) CALL mp_stop(ierr, "mpi_allreduce @ "//routineN)
         CALL add_perf(perf_id=3, msg_size=msglen*int_8_size)
#else
         MARK_USED(msg)
         MARK_USED(gid)
#endif
         CALL timestop(handle)
      END SUBROUTINE mp_prod_l