/* -*- 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"

/* Pairwise Exchange

 *

 * We use a pairwise exchange algorithm similar to the one used in

 * intracommunicator alltoall for long messages.  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.

 */

#undef FUNCNAME

#define FUNCNAME MPIR_Ialltoall_sched_inter_pairwise_exchange

#undef FCNAME

#define FCNAME MPL_QUOTE(FUNCNAME)

int MPIR_Ialltoall_sched_inter_pairwise_exchange(const void *sendbuf, int sendcount,

                                                 MPI_Datatype sendtype, void *recvbuf,

                                                 int recvcount, MPI_Datatype recvtype,

                                                 MPIR_Comm * comm_ptr, MPIR_Sched_t s)

{

    int mpi_errno = MPI_SUCCESS;

    int local_size, remote_size, max_size, i;

    MPI_Aint sendtype_extent, recvtype_extent;

    int src, dst, rank;

    char *sendaddr, *recvaddr;

    local_size = comm_ptr->local_size;

    remote_size = comm_ptr->remote_size;

    rank = comm_ptr->rank;

    /* Get extent of send and recv types */

    MPIR_Datatype_get_extent_macro(sendtype, sendtype_extent);

    MPIR_Datatype_get_extent_macro(recvtype, recvtype_extent);

    /* Do the pairwise exchanges */

    max_size = MPL_MAX(local_size, remote_size);

    MPIR_Ensure_Aint_fits_in_pointer(MPIR_VOID_PTR_CAST_TO_MPI_AINT recvbuf +

                                     max_size * recvcount * recvtype_extent);

    MPIR_Ensure_Aint_fits_in_pointer(MPIR_VOID_PTR_CAST_TO_MPI_AINT sendbuf +

                                     max_size * sendcount * sendtype_extent);

    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;

        } else {

            recvaddr = (char *) recvbuf + src * recvcount * recvtype_extent;

        }

        if (dst >= remote_size) {

            dst = MPI_PROC_NULL;

            sendaddr = NULL;

        } else {

            sendaddr = (char *) sendbuf + dst * sendcount * sendtype_extent;

        }

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

        if (mpi_errno)

            MPIR_ERR_POP(mpi_errno);

        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;

}