// Copyright (C) 2005, 2006 Douglas Gregor.



// Use, modification and distribution is subject to the Boost Software

// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at

// http://www.boost.org/LICENSE_1_0.txt)



// Message Passing Interface 1.1 -- Section 4.5. Gather

#ifndef BOOST_MPI_GATHER_HPP

#define BOOST_MPI_GATHER_HPP



#include <boost/mpi/exception.hpp>

#include <boost/mpi/datatype.hpp>

#include <vector>

#include <boost/mpi/packed_oarchive.hpp>

#include <boost/mpi/packed_iarchive.hpp>

#include <boost/mpi/detail/point_to_point.hpp>

#include <boost/mpi/communicator.hpp>

#include <boost/mpi/environment.hpp>

#include <boost/assert.hpp>



namespace boost { namespace mpi {



namespace detail {

  // We're gathering at the root for a type that has an associated MPI

  // datatype, so we'll use MPI_Gather to do all of the work.

  template<typename T>

  void

  gather_impl(const communicator& comm, const T* in_values, int n, 

              T* out_values, int root, mpl::true_)

  {

    MPI_Datatype type = get_mpi_datatype<T>(*in_values);

    BOOST_MPI_CHECK_RESULT(MPI_Gather,

                           (const_cast<T*>(in_values), n, type,

                            out_values, n, type, root, comm));

  }



  // We're gathering from a non-root for a type that has an associated MPI

  // datatype, so we'll use MPI_Gather to do all of the work.

  template<typename T>

  void

  gather_impl(const communicator& comm, const T* in_values, int n, int root, 

              mpl::true_)

  {

    MPI_Datatype type = get_mpi_datatype<T>(*in_values);

    BOOST_MPI_CHECK_RESULT(MPI_Gather,

                           (const_cast<T*>(in_values), n, type,

                            0, n, type, root, comm));

  }



  // We're gathering at the root for a type that does not have an

  // associated MPI datatype, so we'll need to serialize

  // it. Unfortunately, this means that we cannot use MPI_Gather, so

  // we'll just have all of the non-root nodes send individual

  // messages to the root.

  template<typename T>

  void

  gather_impl(const communicator& comm, const T* in_values, int n, 

              T* out_values, int root, mpl::false_)

  {

    int tag = environment::collectives_tag();

    int size = comm.size();



    for (int src = 0; src < size; ++src) {

      if (src == root)

        std::copy(in_values, in_values + n, out_values + n * src);

      else

        comm.recv(src, tag, out_values + n * src, n);

    }

  }



  // We're gathering at a non-root for a type that does not have an

  // associated MPI datatype, so we'll need to serialize

  // it. Unfortunately, this means that we cannot use MPI_Gather, so

  // we'll just have all of the non-root nodes send individual

  // messages to the root.

  template<typename T>

  void

  gather_impl(const communicator& comm, const T* in_values, int n, int root, 

              mpl::false_)

  {

    int tag = environment::collectives_tag();

    comm.send(root, tag, in_values, n);

  }

} // end namespace detail



template<typename T>

void

gather(const communicator& comm, const T& in_value, T* out_values, int root)

{

  if (comm.rank() == root)

    detail::gather_impl(comm, &in_value, 1, out_values, root, 

                        is_mpi_datatype<T>());

  else

    detail::gather_impl(comm, &in_value, 1, root, is_mpi_datatype<T>());

}



template<typename T>

void gather(const communicator& comm, const T& in_value, int root)

{

  BOOST_ASSERT(comm.rank() != root);

  detail::gather_impl(comm, &in_value, 1, root, is_mpi_datatype<T>());

}



template<typename T>

void

gather(const communicator& comm, const T& in_value, std::vector<T>& out_values,

       int root)

{

  if (comm.rank() == root) {

    out_values.resize(comm.size());

    ::boost::mpi::gather(comm, in_value, &out_values[0], root);

  } else {

    ::boost::mpi::gather(comm, in_value, root);

  }

}



template<typename T>

void

gather(const communicator& comm, const T* in_values, int n, T* out_values, 

       int root)

{

  if (comm.rank() == root)

    detail::gather_impl(comm, in_values, n, out_values, root, 

                        is_mpi_datatype<T>());

  else

    detail::gather_impl(comm, in_values, n, root, is_mpi_datatype<T>());

}



template<typename T>

void

gather(const communicator& comm, const T* in_values, int n, 

       std::vector<T>& out_values, int root)

{

  ::boost::mpi::gather(comm, in_values, n, &out_values[0], root);

}



template<typename T>

void gather(const communicator& comm, const T* in_values, int n, int root)

{

  BOOST_ASSERT(comm.rank() != root);

  detail::gather_impl(comm, in_values, n, root, is_mpi_datatype<T>());

}





} } // end namespace boost::mpi



#endif // BOOST_MPI_GATHER_HPP

