compute/algorithm/random_shuffle.hpp

0001 //---------------------------------------------------------------------------//
0002 // Copyright (c) 2013 Kyle Lutz <kyle.r.lutz@gmail.com>
0003 //
0004 // Distributed under the Boost Software License, Version 1.0
0005 // See accompanying file LICENSE_1_0.txt or copy at
0006 // http://www.boost.org/LICENSE_1_0.txt
0007 //
0008 // See http://boostorg.github.com/compute for more information.
0009 //---------------------------------------------------------------------------//
0010
0011 #ifndef BOOST_COMPUTE_ALGORITHM_RANDOM_SHUFFLE_HPP
0012 #define BOOST_COMPUTE_ALGORITHM_RANDOM_SHUFFLE_HPP
0013
0014 #include <vector>
0015 #include <algorithm>
0016
0017 #ifdef BOOST_COMPUTE_USE_CPP11
0018 #include <random>
0019 #endif
0020
0021 #include <boost/static_assert.hpp>
0022 #include <boost/range/algorithm_ext/iota.hpp>
0023
0024 #include <boost/compute/system.hpp>
0025 #include <boost/compute/functional.hpp>
0026 #include <boost/compute/command_queue.hpp>
0027 #include <boost/compute/container/vector.hpp>
0028 #include <boost/compute/algorithm/scatter.hpp>
0029 #include <boost/compute/detail/iterator_range_size.hpp>
0030 #include <boost/compute/type_traits/is_device_iterator.hpp>
0031
0032 namespace boost {
0033 namespace compute {
0034
0035 /// Randomly shuffles the elements in the range [\p first, \p last).
0036 ///
0037 /// Space complexity: \Omega(2n)
0038 ///
0039 /// \see scatter()
0040 template<class Iterator>
0041 inline void random_shuffle(Iterator first,
0042                            Iterator last,
0043                            command_queue &queue = system::default_queue())
0044 {
0045     BOOST_STATIC_ASSERT(is_device_iterator<Iterator>::value);
0046     typedef typename std::iterator_traits<Iterator>::value_type value_type;
0047
0048     size_t count = detail::iterator_range_size(first, last);
0049     if(count == 0){
0050         return;
0051     }
0052
0053     // generate shuffled indices on the host
0054     std::vector<cl_uint> random_indices(count);
0055     boost::iota(random_indices, 0);
0056 #ifdef BOOST_COMPUTE_USE_CPP11
0057     std::random_device nondeterministic_randomness;
0058     std::default_random_engine random_engine(nondeterministic_randomness());
0059     std::shuffle(random_indices.begin(), random_indices.end(), random_engine);
0060 #else
0061     std::random_shuffle(random_indices.begin(), random_indices.end());
0062 #endif
0063
0064     // copy random indices to the device
0065     const context &context = queue.get_context();
0066     vector<cl_uint> indices(count, context);
0067     ::boost::compute::copy(random_indices.begin(),
0068                            random_indices.end(),
0069                            indices.begin(),
0070                            queue);
0071
0072     // make a copy of the values on the device
0073     vector<value_type> tmp(count, context);
0074     ::boost::compute::copy(first,
0075                            last,
0076                            tmp.begin(),
0077                            queue);
0078
0079     // write values to their new locations
0080     ::boost::compute::scatter(tmp.begin(),
0081                               tmp.end(),
0082                               indices.begin(),
0083                               first,
0084                               queue);
0085 }
0086
0087 } // end compute namespace
0088 } // end boost namespace
0089
0090 #endif // BOOST_COMPUTE_ALGORITHM_RANDOM_SHUFFLE_HPP