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

/*

 *

 *  (C) 2001 by Argonne National Laboratory.

 *      See COPYRIGHT in top-level directory.

 */

#include "mpiimpl.h"

/*

 * Pairwise Exchange

 *

 * 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 alltoallv

 */

#undef FUNCNAME

#define FUNCNAME MPIR_Alltoallw_inter_pairwise_exchange

#undef FCNAME

#define FCNAME MPL_QUOTE(FUNCNAME)

int MPIR_Alltoallw_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_Errflag_t * errflag)

{

    int local_size, remote_size, max_size, i;

    int mpi_errno = MPI_SUCCESS;

    int mpi_errno_ret = MPI_SUCCESS;

    MPI_Status status;

    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 = MPIC_Sendrecv(sendaddr, sendcount, sendtype,

                                  dst, MPIR_ALLTOALLW_TAG, recvaddr,

                                  recvcount, recvtype, src,

                                  MPIR_ALLTOALLW_TAG, comm_ptr, &status, errflag);

        if (mpi_errno) {

            /* for communication errors, just record the error but continue */

            *errflag =

                MPIX_ERR_PROC_FAILED ==

                MPIR_ERR_GET_CLASS(mpi_errno) ? MPIR_ERR_PROC_FAILED : MPIR_ERR_OTHER;

            MPIR_ERR_SET(mpi_errno, *errflag, "**fail");

            MPIR_ERR_ADD(mpi_errno_ret, mpi_errno);

        }

    }

    if (mpi_errno_ret)

        mpi_errno = mpi_errno_ret;

    else if (*errflag != MPIR_ERR_NONE)

        MPIR_ERR_SET(mpi_errno, *errflag, "**coll_fail");

    return mpi_errno;

}