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// Copyright (C) 2005-2006 Douglas Gregor <doug.gregor@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. Scan
#ifndef BOOST_MPI_SCAN_HPP
#define BOOST_MPI_SCAN_HPP
#include <boost/mpi/exception.hpp>
#include <boost/mpi/datatype.hpp>
// For (de-)serializing sends and receives
#include <boost/mpi/packed_oarchive.hpp>
#include <boost/mpi/packed_iarchive.hpp>
// For packed_[io]archive sends and receives
#include <boost/mpi/detail/point_to_point.hpp>
#include <boost/mpi/communicator.hpp>
#include <boost/mpi/environment.hpp>
#include <boost/mpi/detail/computation_tree.hpp>
#include <boost/mpi/operations.hpp>
#include <algorithm>
#include <exception>
#include <boost/assert.hpp>
namespace boost { namespace mpi {
/************************************************************************
* Implementation details *
************************************************************************/
namespace detail {
/**********************************************************************
* Simple prefix reduction with MPI_Scan *
**********************************************************************/
// We are performing prefix reduction for a type that has an
// associated MPI datatype and operation, so we'll use MPI_Scan
// directly.
template<typename T, typename Op>
void
scan_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_Scan,
(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 prefix reduction with MPI_Scan *
**********************************************************************/
// We are performing prefix reduction for a type that has an
// associated MPI datatype but with a custom operation. We'll use
// MPI_Scan directly, but we'll need to create an MPI_Op manually.
template<typename T, typename Op>
void
scan_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_Scan,
(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 *
**********************************************************************/
template<typename T, typename Op>
void
upper_lower_scan(const communicator& comm, const T* in_values, int n,
T* out_values, Op& op, int lower, int upper)
{
int tag = environment::collectives_tag();
int rank = comm.rank();
if (lower + 1 == upper) {
std::copy(in_values, in_values + n, out_values);
} else {
int middle = (lower + upper) / 2;
if (rank < middle) {
// Lower half
upper_lower_scan(comm, in_values, n, out_values, op, lower, middle);
// If we're the last process in the lower half, send our values
// to everyone in the upper half.
if (rank == middle - 1) {
packed_oarchive oa(comm);
for (int i = 0; i < n; ++i)
oa << out_values[i];
for (int p = middle; p < upper; ++p)
comm.send(p, tag, oa);
}
} else {
// Upper half
upper_lower_scan(comm, in_values, n, out_values, op, middle, upper);
// Receive value from the last process in the lower half.
packed_iarchive ia(comm);
comm.recv(middle - 1, tag, ia);
// Combine value that came from the left with our value
T left_value;
for (int i = 0; i < n; ++i)
{
ia >> left_value;
out_values[i] = op(left_value, out_values[i]);
}
}
}
}
// We are performing prefix reduction for a type that has no
// associated MPI datatype and operation, so we'll use a simple
// upper/lower algorithm.
template<typename T, typename Op>
inline void
scan_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*/)
{
upper_lower_scan(comm, in_values, n, out_values, op, 0, comm.size());
}
} // end namespace detail
template<typename T, typename Op>
inline void
scan(const communicator& comm, const T& in_value, T& out_value, Op op)
{
detail::scan_impl(comm, &in_value, 1, &out_value, op,
is_mpi_op<Op, T>(), is_mpi_datatype<T>());
}
template<typename T, typename Op>
inline void
scan(const communicator& comm, const T* in_values, int n, T* out_values, Op op)
{
detail::scan_impl(comm, in_values, n, out_values, op,
is_mpi_op<Op, T>(), is_mpi_datatype<T>());
}
template<typename T, typename Op>
inline T
scan(const communicator& comm, const T& in_value, Op op)
{
T out_value;
detail::scan_impl(comm, &in_value, 1, &out_value, op,
is_mpi_op<Op, T>(), is_mpi_datatype<T>());
return out_value;
}
} } // end namespace boost::mpi
#endif // BOOST_MPI_SCAN_HPP
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