text: /*
   * Copyright (c) 2006      The Trustees of Indiana University and Indiana
   *                         University Research and Technology
   *                         Corporation.  All rights reserved.
   * Copyright (c) 2006      The Technical University of Chemnitz. All
   *                         rights reserved.
   * Copyright (c) 2014      Research Organization for Information Science
   *                         and Technology (RIST). All rights reserved.
   *
   * Author(s): Torsten Hoefler <htor@cs.indiana.edu>
   *
   */
  
  #include "comm_helpers.h"
  
  int ompi_comm_neighbors_count(MPI_Comm comm, int *indegree, int *outdegree, int *weighted) {
      int res;
  
      if (OMPI_COMM_IS_CART(comm)) { 
          int ndims;
          res = MPI_Cartdim_get(comm, &ndims)  ;
          if (MPI_SUCCESS != res) {
              return res;
          }
          /* outdegree is always 2*ndims because we need to iterate over empty buffers for MPI_PROC_NULL */
          *outdegree = *indegree = 2*ndims;
          *weighted = 0;
      } else if (OMPI_COMM_IS_GRAPH(comm)) {
          int rank, nneighbors;
          MPI_Comm_rank(comm, &rank);
          res = MPI_Graph_neighbors_count(comm, rank, &nneighbors);
          if (MPI_SUCCESS != res) {
              return res;
          }
          *outdegree = *indegree = nneighbors;
          *weighted = 0;
      } else if (OMPI_COMM_IS_DIST_GRAPH(comm)) {
          res = MPI_Dist_graph_neighbors_count(comm, indegree, outdegree, weighted);
      } else {
          return MPI_ERR_ARG;
      }
  
      return MPI_SUCCESS;
  }
  
  int ompi_comm_neighbors(MPI_Comm comm, int maxindegree, int sources[], int sourceweights[], int maxoutdegree, int destinations[], int destweights[]) {
      int res;
      int index = 0;
  
      int indeg, outdeg, wgtd;
      res = ompi_comm_neighbors_count(comm, &indeg, &outdeg, &wgtd);
      if (MPI_SUCCESS != res) {
          return res;
      }
      if(indeg > maxindegree && outdeg > maxoutdegree) return MPI_ERR_TRUNCATE; /* we want to return *all* neighbors */
  
      if (OMPI_COMM_IS_CART(comm)) { 
          int ndims, i, rpeer, speer;
          res = MPI_Cartdim_get(comm, &ndims);
          if (MPI_SUCCESS != res) {
              return res;
          }
  
          for(i = 0; i<ndims; i++) {
            res = MPI_Cart_shift(comm, i, 1, &rpeer, &speer);
            if (MPI_SUCCESS != res) {
                return res;
            }
            sources[index] = destinations[index] = rpeer; index++;
            sources[index] = destinations[index] = speer; index++;
          }
      } else if (OMPI_COMM_IS_GRAPH(comm)) {
          int rank;
          MPI_Comm_rank(comm, &rank);
          res = MPI_Graph_neighbors(comm, rank, maxindegree, sources);
          if (MPI_SUCCESS != res) {
              return res;
          }
          for(int i=0; i<maxindegree; i++) destinations[i] = sources[i];
      } else if (OMPI_COMM_IS_DIST_GRAPH(comm)) {
          res = MPI_Dist_graph_neighbors(comm, maxindegree, sources, sourceweights, maxoutdegree, destinations, destweights);
          if (MPI_SUCCESS != res) {
              return res;
          }
      } else {
          return MPI_ERR_ARG;
      }
  
      return MPI_SUCCESS;
  }
  