ceph/src/boost/libs/compute/include/boost/compute/algorithm/random_shuffle.hpp

   1 //---------------------------------------------------------------------------//
   2 // Copyright (c) 2013 Kyle Lutz <kyle.r.lutz@gmail.com>
   3 //
   4 // Distributed under the Boost Software License, Version 1.0
   5 // See accompanying file LICENSE_1_0.txt or copy at
   6 // http://www.boost.org/LICENSE_1_0.txt
   7 //
   8 // See http://boostorg.github.com/compute for more information.
   9 //---------------------------------------------------------------------------//
  10
  11 #ifndef BOOST_COMPUTE_ALGORITHM_RANDOM_SHUFFLE_HPP
  12 #define BOOST_COMPUTE_ALGORITHM_RANDOM_SHUFFLE_HPP
  13
  14 #include <vector>
  15 #include <algorithm>
  16
  17 #include <boost/range/algorithm_ext/iota.hpp>
  18
  19 #include <boost/compute/system.hpp>
  20 #include <boost/compute/functional.hpp>
  21 #include <boost/compute/command_queue.hpp>
  22 #include <boost/compute/container/vector.hpp>
  23 #include <boost/compute/algorithm/scatter.hpp>
  24 #include <boost/compute/detail/iterator_range_size.hpp>
  25
  26 namespace boost {
  27 namespace compute {
  28
  29 /// Randomly shuffles the elements in the range [\p first, \p last).
  30 ///
  31 /// \see scatter()
  32 template<class Iterator>
  33 inline void random_shuffle(Iterator first,
  34                            Iterator last,
  35                            command_queue &queue = system::default_queue())
  36 {
  37     typedef typename std::iterator_traits<Iterator>::value_type value_type;
  38
  39     size_t count = detail::iterator_range_size(first, last);
  40     if(count == 0){
  41         return;
  42     }
  43
  44     // generate shuffled indices on the host
  45     std::vector<cl_uint> random_indices(count);
  46     boost::iota(random_indices, 0);
  47     std::random_shuffle(random_indices.begin(), random_indices.end());
  48
  49     // copy random indices to the device
  50     const context &context = queue.get_context();
  51     vector<cl_uint> indices(count, context);
  52     ::boost::compute::copy(random_indices.begin(),
  53                            random_indices.end(),
  54                            indices.begin(),
  55                            queue);
  56
  57     // make a copy of the values on the device
  58     vector<value_type> tmp(count, context);
  59     ::boost::compute::copy(first,
  60                            last,
  61                            tmp.begin(),
  62                            queue);
  63
  64     // write values to their new locations
  65     ::boost::compute::scatter(tmp.begin(),
  66                               tmp.end(),
  67                               indices.begin(),
  68                               first,
  69                               queue);
  70 }
  71
  72 } // end compute namespace
  73 } // end boost namespace
  74
  75 #endif // BOOST_COMPUTE_ALGORITHM_RANDOM_SHUFFLE_HPP