hypercube_allgatherv.cc

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/*******************************************************************************
 * \copyright   This file is part of the GADGET4 N-body/SPH code developed
 * \copyright   by Volker Springel. Copyright (C) 2014-2020 by Volker Springel
 * \copyright   (vspringel@mpa-garching.mpg.de) and all contributing authors.
 *******************************************************************************/
 
#include "gadgetconfig.h"
 
#include <math.h>
#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#include "../data/allvars.h"
#include "../data/dtypes.h"
 
#ifdef MPI_HYPERCUBE_ALLGATHERV
 
#define TAG 100
 
int MPI_hypercube_Allgatherv(void *sendbuf, int sendcount, MPI_Datatype sendtype, void *recvbuf, int *recvcount, int *displs,
                             MPI_Datatype recvtype, MPI_Comm comm)
{
  int ntask, thistask, ptask, ngrp, size_sendtype, size_recvtype;
  MPI_Status status;
 
  MPI_Comm_rank(comm, &thistask);
  MPI_Comm_size(comm, &ntask);
 
  MPI_Type_size(sendtype, &size_sendtype);
  MPI_Type_size(recvtype, &size_recvtype);
 
  for(ptask = 0; ntask > (1 << ptask); ptask++)
    ;
 
  for(ngrp = 1; ngrp < (1 << ptask); ngrp++)
    {
      int recvtask = thistask ^ ngrp;
 
      if(recvtask < ntask)
        MPI_Sendrecv(sendbuf, sendcount, sendtype, recvtask, TAG, (char *)recvbuf + displs[recvtask] * size_recvtype,
                     recvcount[recvtask], recvtype, recvtask, TAG, comm, &status);
    }
 
  if((char *)sendbuf != (char *)recvbuf + displs[thistask] * size_recvtype)
    memcpy((char *)recvbuf + displs[thistask] * size_recvtype, sendbuf, sendcount * size_sendtype);
 
  return 0;
}
 
#endif