377 lines
13 KiB
C++
377 lines
13 KiB
C++
// Copyright (C) 2005-2006 Douglas Gregor <doug.gregor@gmail.com>.
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// Copyright (C) 2004 The Trustees of Indiana University
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// Use, modification and distribution is subject to the Boost Software
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// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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// Authors: Douglas Gregor
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// Andrew Lumsdaine
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// Message Passing Interface 1.1 -- Section 4.9.1. Reduce
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#ifndef BOOST_MPI_REDUCE_HPP
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#define BOOST_MPI_REDUCE_HPP
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#include <boost/mpi/exception.hpp>
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#include <boost/mpi/datatype.hpp>
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// For (de-)serializing sends and receives
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#include <boost/mpi/packed_oarchive.hpp>
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#include <boost/mpi/packed_iarchive.hpp>
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// For packed_[io]archive sends and receives
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#include <boost/mpi/detail/point_to_point.hpp>
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#include <boost/mpi/communicator.hpp>
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#include <boost/mpi/environment.hpp>
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#include <boost/mpi/detail/computation_tree.hpp>
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#include <boost/mpi/operations.hpp>
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#include <algorithm>
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#include <exception>
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#include <boost/assert.hpp>
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#include <boost/scoped_array.hpp>
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namespace boost { namespace mpi {
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/************************************************************************
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* Implementation details *
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************************************************************************/
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namespace detail {
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/**********************************************************************
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* Simple reduction with MPI_Reduce *
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**********************************************************************/
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// We are reducing at the root for a type that has an associated MPI
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// datatype and operation, so we'll use MPI_Reduce directly.
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template<typename T, typename Op>
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void
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reduce_impl(const communicator& comm, const T* in_values, int n,
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T* out_values, Op /*op*/, int root, mpl::true_ /*is_mpi_op*/,
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mpl::true_/*is_mpi_datatype*/)
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{
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BOOST_MPI_CHECK_RESULT(MPI_Reduce,
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(const_cast<T*>(in_values), out_values, n,
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boost::mpi::get_mpi_datatype<T>(*in_values),
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(is_mpi_op<Op, T>::op()), root, comm));
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}
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// We are reducing to the root for a type that has an associated MPI
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// datatype and operation, so we'll use MPI_Reduce directly.
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template<typename T, typename Op>
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void
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reduce_impl(const communicator& comm, const T* in_values, int n, Op /*op*/,
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int root, mpl::true_ /*is_mpi_op*/, mpl::true_/*is_mpi_datatype*/)
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{
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BOOST_MPI_CHECK_RESULT(MPI_Reduce,
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(const_cast<T*>(in_values), 0, n,
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boost::mpi::get_mpi_datatype<T>(*in_values),
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(is_mpi_op<Op, T>::op()), root, comm));
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}
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/**********************************************************************
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* User-defined reduction with MPI_Reduce *
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**********************************************************************/
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// We are reducing at the root for a type that has an associated MPI
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// datatype but with a custom operation. We'll use MPI_Reduce
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// directly, but we'll need to create an MPI_Op manually.
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template<typename T, typename Op>
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void
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reduce_impl(const communicator& comm, const T* in_values, int n,
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T* out_values, Op op, int root, mpl::false_ /*is_mpi_op*/,
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mpl::true_/*is_mpi_datatype*/)
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{
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user_op<Op, T> mpi_op(op);
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BOOST_MPI_CHECK_RESULT(MPI_Reduce,
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(const_cast<T*>(in_values), out_values, n,
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boost::mpi::get_mpi_datatype<T>(*in_values),
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mpi_op.get_mpi_op(), root, comm));
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}
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// We are reducing to the root for a type that has an associated MPI
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// datatype but with a custom operation. We'll use MPI_Reduce
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// directly, but we'll need to create an MPI_Op manually.
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template<typename T, typename Op>
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void
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reduce_impl(const communicator& comm, const T* in_values, int n, Op op,
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int root, mpl::false_/*is_mpi_op*/, mpl::true_/*is_mpi_datatype*/)
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{
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user_op<Op, T> mpi_op(op);
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BOOST_MPI_CHECK_RESULT(MPI_Reduce,
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(const_cast<T*>(in_values), 0, n,
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boost::mpi::get_mpi_datatype<T>(*in_values),
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mpi_op.get_mpi_op(), root, comm));
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}
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/**********************************************************************
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* User-defined, tree-based reduction for non-MPI data types *
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**********************************************************************/
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// Commutative reduction
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template<typename T, typename Op>
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void
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tree_reduce_impl(const communicator& comm, const T* in_values, int n,
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T* out_values, Op op, int root,
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mpl::true_ /*is_commutative*/)
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{
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std::copy(in_values, in_values + n, out_values);
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int size = comm.size();
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int rank = comm.rank();
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// The computation tree we will use.
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detail::computation_tree tree(rank, size, root);
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int tag = environment::collectives_tag();
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MPI_Status status;
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int children = 0;
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for (int child = tree.child_begin();
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children < tree.branching_factor() && child != root;
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++children, child = (child + 1) % size) {
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// Receive archive
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packed_iarchive ia(comm);
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detail::packed_archive_recv(comm, child, tag, ia, status);
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T incoming;
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for (int i = 0; i < n; ++i) {
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ia >> incoming;
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out_values[i] = op(out_values[i], incoming);
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}
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}
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// For non-roots, send the result to the parent.
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if (tree.parent() != rank) {
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packed_oarchive oa(comm);
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for (int i = 0; i < n; ++i)
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oa << out_values[i];
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detail::packed_archive_send(comm, tree.parent(), tag, oa);
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}
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}
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// Commutative reduction from a non-root.
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template<typename T, typename Op>
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void
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tree_reduce_impl(const communicator& comm, const T* in_values, int n, Op op,
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int root, mpl::true_ /*is_commutative*/)
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{
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scoped_array<T> results(new T[n]);
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detail::tree_reduce_impl(comm, in_values, n, results.get(), op, root,
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mpl::true_());
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}
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// Non-commutative reduction
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template<typename T, typename Op>
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void
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tree_reduce_impl(const communicator& comm, const T* in_values, int n,
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T* out_values, Op op, int root,
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mpl::false_ /*is_commutative*/)
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{
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int tag = environment::collectives_tag();
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int left_child = root / 2;
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int right_child = (root + comm.size()) / 2;
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MPI_Status status;
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if (left_child != root) {
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// Receive value from the left child and merge it with the value
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// we had incoming.
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packed_iarchive ia(comm);
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detail::packed_archive_recv(comm, left_child, tag, ia, status);
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T incoming;
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for (int i = 0; i < n; ++i) {
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ia >> incoming;
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out_values[i] = op(incoming, in_values[i]);
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}
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} else {
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// There was no left value, so copy our incoming value.
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std::copy(in_values, in_values + n, out_values);
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}
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if (right_child != root) {
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// Receive value from the right child and merge it with the
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// value we had incoming.
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packed_iarchive ia(comm);
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detail::packed_archive_recv(comm, right_child, tag, ia, status);
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T incoming;
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for (int i = 0; i < n; ++i) {
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ia >> incoming;
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out_values[i] = op(out_values[i], incoming);
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}
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}
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}
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// Non-commutative reduction from a non-root.
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template<typename T, typename Op>
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void
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tree_reduce_impl(const communicator& comm, const T* in_values, int n, Op op,
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int root, mpl::false_ /*is_commutative*/)
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{
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int size = comm.size();
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int rank = comm.rank();
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int tag = environment::collectives_tag();
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// Determine our parents and children in the commutative binary
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// computation tree.
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int grandparent = root;
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int parent = root;
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int left_bound = 0;
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int right_bound = size;
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int left_child, right_child;
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do {
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left_child = (left_bound + parent) / 2;
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right_child = (parent + right_bound) / 2;
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if (rank < parent) {
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// Go left.
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grandparent = parent;
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right_bound = parent;
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parent = left_child;
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} else if (rank > parent) {
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// Go right.
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grandparent = parent;
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left_bound = parent + 1;
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parent = right_child;
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} else {
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// We've found the parent
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break;
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}
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} while (true);
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// Our parent is the grandparent of our children. This is a slight
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// abuse of notation, but it makes the send-to-parent below make
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// more sense.
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parent = grandparent;
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MPI_Status status;
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scoped_array<T> out_values(new T[n]);
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if (left_child != rank) {
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// Receive value from the left child and merge it with the value
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// we had incoming.
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packed_iarchive ia(comm);
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detail::packed_archive_recv(comm, left_child, tag, ia, status);
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T incoming;
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for (int i = 0; i < n; ++i) {
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ia >> incoming;
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out_values[i] = op(incoming, in_values[i]);
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}
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} else {
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// There was no left value, so copy our incoming value.
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std::copy(in_values, in_values + n, out_values.get());
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}
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if (right_child != rank) {
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// Receive value from the right child and merge it with the
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// value we had incoming.
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packed_iarchive ia(comm);
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detail::packed_archive_recv(comm, right_child, tag, ia, status);
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T incoming;
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for (int i = 0; i < n; ++i) {
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ia >> incoming;
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out_values[i] = op(out_values[i], incoming);
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}
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}
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// Send the combined value to our parent.
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packed_oarchive oa(comm);
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for (int i = 0; i < n; ++i)
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oa << out_values[i];
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detail::packed_archive_send(comm, parent, tag, oa);
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}
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// We are reducing at the root for a type that has no associated MPI
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// datatype and operation, so we'll use a simple tree-based
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// algorithm.
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template<typename T, typename Op>
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void
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reduce_impl(const communicator& comm, const T* in_values, int n,
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T* out_values, Op op, int root, mpl::false_ /*is_mpi_op*/,
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mpl::false_ /*is_mpi_datatype*/)
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{
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detail::tree_reduce_impl(comm, in_values, n, out_values, op, root,
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is_commutative<Op, T>());
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}
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// We are reducing to the root for a type that has no associated MPI
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// datatype and operation, so we'll use a simple tree-based
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// algorithm.
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template<typename T, typename Op>
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void
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reduce_impl(const communicator& comm, const T* in_values, int n, Op op,
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int root, mpl::false_ /*is_mpi_op*/,
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mpl::false_ /*is_mpi_datatype*/)
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{
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detail::tree_reduce_impl(comm, in_values, n, op, root,
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is_commutative<Op, T>());
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}
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} // end namespace detail
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template<typename T, typename Op>
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void
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reduce(const communicator& comm, const T* in_values, int n, T* out_values,
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Op op, int root)
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{
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if (comm.rank() == root)
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detail::reduce_impl(comm, in_values, n, out_values, op, root,
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is_mpi_op<Op, T>(), is_mpi_datatype<T>());
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else
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detail::reduce_impl(comm, in_values, n, op, root,
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is_mpi_op<Op, T>(), is_mpi_datatype<T>());
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}
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template<typename T, typename Op>
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void
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reduce(const communicator& comm, const T* in_values, int n, Op op, int root)
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{
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BOOST_ASSERT(comm.rank() != root);
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detail::reduce_impl(comm, in_values, n, op, root,
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is_mpi_op<Op, T>(), is_mpi_datatype<T>());
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}
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template<typename T, typename Op>
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void
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reduce(const communicator & comm, std::vector<T> const & in_values, Op op,
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int root)
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{
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reduce(comm, &in_values.front(), in_values.size(), op, root);
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}
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template<typename T, typename Op>
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void
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reduce(const communicator & comm, std::vector<T> const & in_values,
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std::vector<T> & out_values, Op op, int root)
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{
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if (root == comm.rank()) out_values.resize(in_values.size());
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reduce(comm, &in_values.front(), in_values.size(), &out_values.front(), op,
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root);
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}
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template<typename T, typename Op>
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void
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reduce(const communicator& comm, const T& in_value, T& out_value, Op op,
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int root)
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{
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if (comm.rank() == root)
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detail::reduce_impl(comm, &in_value, 1, &out_value, op, root,
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is_mpi_op<Op, T>(), is_mpi_datatype<T>());
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else
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detail::reduce_impl(comm, &in_value, 1, op, root,
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is_mpi_op<Op, T>(), is_mpi_datatype<T>());
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}
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template<typename T, typename Op>
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void reduce(const communicator& comm, const T& in_value, Op op, int root)
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{
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BOOST_ASSERT(comm.rank() != root);
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detail::reduce_impl(comm, &in_value, 1, op, root,
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is_mpi_op<Op, T>(), is_mpi_datatype<T>());
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}
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} } // end namespace boost::mpi
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#endif // BOOST_MPI_REDUCE_HPP
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