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