/* -*- 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;
}