ceph/src/boost/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 /// Space complexity: \Omega(2n)
  32 ///
  33 /// \see scatter()
  34 template<class Iterator>
  35 inline void random_shuffle(Iterator first,
  36                            Iterator last,
  37                            command_queue &queue = system::default_queue())
  38 {
  39     typedef typename std::iterator_traits<Iterator>::value_type value_type;
  40
  41     size_t count = detail::iterator_range_size(first, last);
  42     if(count == 0){
  43         return;
  44     }
  45
  46     // generate shuffled indices on the host
  47     std::vector<cl_uint> random_indices(count);
  48     boost::iota(random_indices, 0);
  49     std::random_shuffle(random_indices.begin(), random_indices.end());
  50
  51     // copy random indices to the device
  52     const context &context = queue.get_context();
  53     vector<cl_uint> indices(count, context);
  54     ::boost::compute::copy(random_indices.begin(),
  55                            random_indices.end(),
  56                            indices.begin(),
  57                            queue);
  58
  59     // make a copy of the values on the device
  60     vector<value_type> tmp(count, context);
  61     ::boost::compute::copy(first,
  62                            last,
  63                            tmp.begin(),
  64                            queue);
  65
  66     // write values to their new locations
  67     ::boost::compute::scatter(tmp.begin(),
  68                               tmp.end(),
  69                               indices.begin(),
  70                               first,
  71                               queue);
  72 }
  73
  74 } // end compute namespace
  75 } // end boost namespace
  76
  77 #endif // BOOST_COMPUTE_ALGORITHM_RANDOM_SHUFFLE_HPP