/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */

/*

 *  (C) 2017 by Argonne National Laboratory.

 *      See COPYRIGHT in top-level directory.

 */

#include "mpiimpl.h"

#undef FUNCNAME

#define FUNCNAME MPIR_Ialltoallw_sched_inter_pairwise_exchange

#undef FCNAME

#define FCNAME MPL_QUOTE(FUNCNAME)

int MPIR_Ialltoallw_sched_inter_pairwise_exchange(const void *sendbuf, const int sendcounts[],

                                                  const int sdispls[],

                                                  const MPI_Datatype sendtypes[], void *recvbuf,

                                                  const int recvcounts[], const int rdispls[],

                                                  const MPI_Datatype recvtypes[],

                                                  MPIR_Comm * comm_ptr, MPIR_Sched_t s)

{

/* Intercommunicator alltoallw. We use a pairwise exchange algorithm

   similar to the one used in intracommunicator alltoallw. Since the local and

   remote groups can be of different sizes, we first compute the max of

   local_group_size, remote_group_size.  At step i, 0 <= i < max_size, each

   process receives from src = (rank - i + max_size) % max_size if src < remote_size,

   and sends to dst = (rank + i) % max_size if dst < remote_size.

   FIXME: change algorithm to match intracommunicator alltoallw

*/

    int mpi_errno = MPI_SUCCESS;

    int local_size, remote_size, max_size, i;

    int src, dst, rank, sendcount, recvcount;

    char *sendaddr, *recvaddr;

    MPI_Datatype sendtype, recvtype;

    local_size = comm_ptr->local_size;

    remote_size = comm_ptr->remote_size;

    rank = comm_ptr->rank;

    /* Use pairwise exchange algorithm. */

    max_size = MPL_MAX(local_size, remote_size);

    for (i = 0; i < max_size; i++) {

        src = (rank - i + max_size) % max_size;

        dst = (rank + i) % max_size;

        if (src >= remote_size) {

            src = MPI_PROC_NULL;

            recvaddr = NULL;

            recvcount = 0;

            recvtype = MPI_DATATYPE_NULL;

        } else {

            recvaddr = (char *) recvbuf + rdispls[src];

            recvcount = recvcounts[src];

            recvtype = recvtypes[src];

        }

        if (dst >= remote_size) {

            dst = MPI_PROC_NULL;

            sendaddr = NULL;

            sendcount = 0;

            sendtype = MPI_DATATYPE_NULL;

        } else {

            sendaddr = (char *) sendbuf + sdispls[dst];

            sendcount = sendcounts[dst];

            sendtype = sendtypes[dst];

        }

        mpi_errno = MPIR_Sched_send(sendaddr, sendcount, sendtype, dst, comm_ptr, s);

        if (mpi_errno)

            MPIR_ERR_POP(mpi_errno);

        /* sendrecv, no barrier here */

        mpi_errno = MPIR_Sched_recv(recvaddr, recvcount, recvtype, src, comm_ptr, s);

        if (mpi_errno)

            MPIR_ERR_POP(mpi_errno);

        MPIR_SCHED_BARRIER(s);

    }

  fn_exit:

    return mpi_errno;

  fn_fail:

    goto fn_exit;

}