ceph/src/boost/libs/compute/include/boost/compute/algorithm/merge.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_MERGE_HPP
  12 #define BOOST_COMPUTE_ALGORITHM_MERGE_HPP
  13
  14 #include <boost/compute/system.hpp>
  15 #include <boost/compute/command_queue.hpp>
  16 #include <boost/compute/algorithm/copy.hpp>
  17 #include <boost/compute/algorithm/detail/merge_with_merge_path.hpp>
  18 #include <boost/compute/algorithm/detail/serial_merge.hpp>
  19 #include <boost/compute/detail/iterator_range_size.hpp>
  20 #include <boost/compute/detail/parameter_cache.hpp>
  21
  22 namespace boost {
  23 namespace compute {
  24
  25 /// Merges the sorted values in the range [\p first1, \p last1) with the sorted
  26 /// values in the range [\p first2, last2) and stores the result in the range
  27 /// beginning at \p result. Values are compared using the \p comp function. If
  28 /// no comparision function is given, \c less is used.
  29 ///
  30 /// \param first1 first element in the first range to merge
  31 /// \param last1 last element in the first range to merge
  32 /// \param first2 first element in the second range to merge
  33 /// \param last2 last element in the second range to merge
  34 /// \param result first element in the result range
  35 /// \param comp comparison function (by default \c less)
  36 /// \param queue command queue to perform the operation
  37 ///
  38 /// \return \c OutputIterator to the end of the result range
  39 ///
  40 /// \see inplace_merge()
  41 template<class InputIterator1,
  42          class InputIterator2,
  43          class OutputIterator,
  44          class Compare>
  45 inline OutputIterator merge(InputIterator1 first1,
  46                             InputIterator1 last1,
  47                             InputIterator2 first2,
  48                             InputIterator2 last2,
  49                             OutputIterator result,
  50                             Compare comp,
  51                             command_queue &queue = system::default_queue())
  52 {
  53     typedef typename std::iterator_traits<InputIterator1>::value_type input1_type;
  54     typedef typename std::iterator_traits<InputIterator2>::value_type input2_type;
  55     typedef typename std::iterator_traits<OutputIterator>::value_type output_type;
  56
  57     const device &device = queue.get_device();
  58
  59     std::string cache_key =
  60         std::string("__boost_merge_") + type_name<input1_type>() + "_"
  61         + type_name<input2_type>() + "_" + type_name<output_type>();
  62     boost::shared_ptr<detail::parameter_cache> parameters =
  63         detail::parameter_cache::get_global_cache(device);
  64
  65     // default serial merge threshold depends on device type
  66     size_t default_serial_merge_threshold = 32768;
  67     if(device.type() & device::gpu) {
  68         default_serial_merge_threshold = 2048;
  69     }
  70
  71     // loading serial merge threshold parameter
  72     const size_t serial_merge_threshold =
  73         parameters->get(cache_key, "serial_merge_threshold",
  74                         static_cast<uint_>(default_serial_merge_threshold));
  75
  76     // choosing merge algorithm
  77     const size_t total_count =
  78         detail::iterator_range_size(first1, last1)
  79         + detail::iterator_range_size(first2, last2);
  80     // for small inputs serial merge turns out to outperform
  81     // merge with merge path algorithm
  82     if(total_count <= serial_merge_threshold){
  83        return detail::serial_merge(first1, last1, first2, last2, result, comp, queue);
  84     }
  85     return detail::merge_with_merge_path(first1, last1, first2, last2, result, comp, queue);
  86 }
  87
  88 /// \overload
  89 template<class InputIterator1, class InputIterator2, class OutputIterator>
  90 inline OutputIterator merge(InputIterator1 first1,
  91                             InputIterator1 last1,
  92                             InputIterator2 first2,
  93                             InputIterator2 last2,
  94                             OutputIterator result,
  95                             command_queue &queue = system::default_queue())
  96 {
  97     typedef typename std::iterator_traits<InputIterator1>::value_type value_type;
  98     less<value_type> less_than;
  99     return merge(first1, last1, first2, last2, result, less_than, queue);
 100 }
 101
 102 } // end compute namespace
 103 } // end boost namespace
 104
 105 #endif // BOOST_COMPUTE_ALGORITHM_MERGE_HPP