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//---------------------------------------------------------------------------//
// Copyright (c) 2013 Kyle Lutz <kyle.r.lutz@gmail.com>
//
// Distributed under 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
//
// See http://boostorg.github.com/compute for more information.
//---------------------------------------------------------------------------//
#ifndef BOOST_COMPUTE_ALGORITHM_RANDOM_SHUFFLE_HPP
#define BOOST_COMPUTE_ALGORITHM_RANDOM_SHUFFLE_HPP
#include <vector>
#include <algorithm>
#ifdef BOOST_COMPUTE_USE_CPP11
#include <random>
#endif
#include <boost/static_assert.hpp>
#include <boost/range/algorithm_ext/iota.hpp>
#include <boost/compute/system.hpp>
#include <boost/compute/functional.hpp>
#include <boost/compute/command_queue.hpp>
#include <boost/compute/container/vector.hpp>
#include <boost/compute/algorithm/scatter.hpp>
#include <boost/compute/detail/iterator_range_size.hpp>
#include <boost/compute/type_traits/is_device_iterator.hpp>
namespace boost {
namespace compute {
/// Randomly shuffles the elements in the range [\p first, \p last).
///
/// Space complexity: \Omega(2n)
///
/// \see scatter()
template<class Iterator>
inline void random_shuffle(Iterator first,
Iterator last,
command_queue &queue = system::default_queue())
{
BOOST_STATIC_ASSERT(is_device_iterator<Iterator>::value);
typedef typename std::iterator_traits<Iterator>::value_type value_type;
size_t count = detail::iterator_range_size(first, last);
if(count == 0){
return;
}
// generate shuffled indices on the host
std::vector<cl_uint> random_indices(count);
boost::iota(random_indices, 0);
#ifdef BOOST_COMPUTE_USE_CPP11
std::random_device nondeterministic_randomness;
std::default_random_engine random_engine(nondeterministic_randomness());
std::shuffle(random_indices.begin(), random_indices.end(), random_engine);
#else
std::random_shuffle(random_indices.begin(), random_indices.end());
#endif
// copy random indices to the device
const context &context = queue.get_context();
vector<cl_uint> indices(count, context);
::boost::compute::copy(random_indices.begin(),
random_indices.end(),
indices.begin(),
queue);
// make a copy of the values on the device
vector<value_type> tmp(count, context);
::boost::compute::copy(first,
last,
tmp.begin(),
queue);
// write values to their new locations
::boost::compute::scatter(tmp.begin(),
tmp.end(),
indices.begin(),
first,
queue);
}
} // end compute namespace
} // end boost namespace
#endif // BOOST_COMPUTE_ALGORITHM_RANDOM_SHUFFLE_HPP
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