Chris@16: // Copyright (C) 2005-2006 Douglas Gregor <doug.gregor -at- gmail.com>
Chris@16: // Copyright (C) 2004 The Trustees of Indiana University
Chris@16: 
Chris@16: // Use, modification and distribution is subject to the Boost Software
Chris@16: // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
Chris@16: // http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: //   Authors: Douglas Gregor
Chris@16: //            Andrew Lumsdaine
Chris@16: 
Chris@16: // Message Passing Interface 1.1 -- Section 4.9.1. Reduce
Chris@16: #ifndef BOOST_MPI_ALL_REDUCE_HPP
Chris@16: #define BOOST_MPI_ALL_REDUCE_HPP
Chris@16: 
Chris@16: #include <vector>
Chris@16: 
Chris@16: #include <boost/mpi/inplace.hpp>
Chris@16: 
Chris@16: // All-reduce falls back to reduce() + broadcast() in some cases.
Chris@16: #include <boost/mpi/collectives/broadcast.hpp>
Chris@16: #include <boost/mpi/collectives/reduce.hpp>
Chris@16: 
Chris@16: namespace boost { namespace mpi {
Chris@16: namespace detail {
Chris@16:   /**********************************************************************
Chris@16:    * Simple reduction with MPI_Allreduce                                *
Chris@16:    **********************************************************************/
Chris@16:   // We are reducing for a type that has an associated MPI
Chris@16:   // datatype and operation, so we'll use MPI_Allreduce directly.
Chris@16:   template<typename T, typename Op>
Chris@16:   void
Chris@16:   all_reduce_impl(const communicator& comm, const T* in_values, int n,
Chris@16:                   T* out_values, Op /*op*/, mpl::true_ /*is_mpi_op*/,
Chris@16:                   mpl::true_ /*is_mpi_datatype*/)
Chris@16:   {
Chris@16:     BOOST_MPI_CHECK_RESULT(MPI_Allreduce,
Chris@16:                            (const_cast<T*>(in_values), out_values, n,
Chris@16:                             boost::mpi::get_mpi_datatype<T>(*in_values),
Chris@16:                             (is_mpi_op<Op, T>::op()), comm));
Chris@16:   }
Chris@16: 
Chris@16:   /**********************************************************************
Chris@16:    * User-defined reduction with MPI_Allreduce                          *
Chris@16:    **********************************************************************/
Chris@16:   // We are reducing at the root for a type that has an associated MPI
Chris@16:   // datatype but with a custom operation. We'll use MPI_Reduce
Chris@16:   // directly, but we'll need to create an MPI_Op manually.
Chris@16:   template<typename T, typename Op>
Chris@16:   void
Chris@16:   all_reduce_impl(const communicator& comm, const T* in_values, int n,
Chris@16:                   T* out_values, Op op, mpl::false_ /*is_mpi_op*/,
Chris@16:                   mpl::true_ /*is_mpi_datatype*/)
Chris@16:   {
Chris@16:     user_op<Op, T> mpi_op(op);
Chris@16:     BOOST_MPI_CHECK_RESULT(MPI_Allreduce,
Chris@16:                            (const_cast<T*>(in_values), out_values, n,
Chris@16:                             boost::mpi::get_mpi_datatype<T>(*in_values),
Chris@16:                             mpi_op.get_mpi_op(), comm));
Chris@16:   }
Chris@16: 
Chris@16:   /**********************************************************************
Chris@16:    * User-defined, tree-based reduction for non-MPI data types          *
Chris@16:    **********************************************************************/
Chris@16:   // We are reducing at the root for a type that has no associated MPI
Chris@16:   // datatype and operation, so we'll use a simple tree-based
Chris@16:   // algorithm.
Chris@16:   template<typename T, typename Op>
Chris@16:   void
Chris@16:   all_reduce_impl(const communicator& comm, const T* in_values, int n,
Chris@16:                   T* out_values, Op op, mpl::false_ /*is_mpi_op*/,
Chris@16:                   mpl::false_ /*is_mpi_datatype*/)
Chris@16:   {
Chris@16:     if (in_values == MPI_IN_PLACE) {
Chris@16:       // if in_values matches the in place tag, then the output
Chris@16:       // buffer actually contains the input data.
Chris@16:       // But we can just go back to the out of place 
Chris@16:       // implementation in this case.
Chris@16:       // it's not clear how/if we can avoid the copy.
Chris@16:       std::vector<T> tmp_in( out_values, out_values + n);
Chris@16:       reduce(comm, &(tmp_in[0]), n, out_values, op, 0);
Chris@16:     } else {
Chris@16:       reduce(comm, in_values, n, out_values, op, 0);
Chris@16:     }
Chris@16:     broadcast(comm, out_values, n, 0);
Chris@16:   }
Chris@16: } // end namespace detail
Chris@16: 
Chris@16: template<typename T, typename Op>
Chris@16: inline void
Chris@16: all_reduce(const communicator& comm, const T* in_values, int n, T* out_values,
Chris@16:            Op op)
Chris@16: {
Chris@16:   detail::all_reduce_impl(comm, in_values, n, out_values, op,
Chris@16:                           is_mpi_op<Op, T>(), is_mpi_datatype<T>());
Chris@16: }
Chris@16: 
Chris@16: template<typename T, typename Op>
Chris@16: inline void
Chris@16: all_reduce(const communicator& comm, inplace_t<T*> inout_values, int n, Op op)
Chris@16: {
Chris@16:   all_reduce(comm, static_cast<const T*>(MPI_IN_PLACE), n, inout_values.buffer, op);
Chris@16: }
Chris@16: 
Chris@16: template<typename T, typename Op>
Chris@16: inline void
Chris@16: all_reduce(const communicator& comm, inplace_t<T> inout_values, Op op)
Chris@16: {
Chris@16:   all_reduce(comm, static_cast<const T*>(MPI_IN_PLACE), 1, &(inout_values.buffer), op);
Chris@16: }
Chris@16: 
Chris@16: template<typename T, typename Op>
Chris@16: inline void
Chris@16: all_reduce(const communicator& comm, const T& in_value, T& out_value, Op op)
Chris@16: {
Chris@16:   detail::all_reduce_impl(comm, &in_value, 1, &out_value, op,
Chris@16:                           is_mpi_op<Op, T>(), is_mpi_datatype<T>());
Chris@16: }
Chris@16: 
Chris@16: template<typename T, typename Op>
Chris@16: T all_reduce(const communicator& comm, const T& in_value, Op op)
Chris@16: {
Chris@16:   T result;
Chris@16:   ::boost::mpi::all_reduce(comm, in_value, result, op);
Chris@16:   return result;
Chris@16: }
Chris@16: 
Chris@16: } } // end namespace boost::mpi
Chris@16: 
Chris@16: #endif // BOOST_MPI_ALL_REDUCE_HPP