ceph/src/boost/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 /// Space complexity: \Omega(distance(\p first1, \p last1) + distance(\p first2, \p last2))
  41 ///
  42 /// \see inplace_merge()
  43 template<class InputIterator1,
  44          class InputIterator2,
  45          class OutputIterator,
  46          class Compare>
  47 inline OutputIterator merge(InputIterator1 first1,
  48                             InputIterator1 last1,
  49                             InputIterator2 first2,
  50                             InputIterator2 last2,
  51                             OutputIterator result,
  52                             Compare comp,
  53                             command_queue &queue = system::default_queue())
  54 {
  55     typedef typename std::iterator_traits<InputIterator1>::value_type input1_type;
  56     typedef typename std::iterator_traits<InputIterator2>::value_type input2_type;
  57     typedef typename std::iterator_traits<OutputIterator>::value_type output_type;
  58
  59     const device &device = queue.get_device();
  60
  61     std::string cache_key =
  62         std::string("__boost_merge_") + type_name<input1_type>() + "_"
  63         + type_name<input2_type>() + "_" + type_name<output_type>();
  64     boost::shared_ptr<detail::parameter_cache> parameters =
  65         detail::parameter_cache::get_global_cache(device);
  66
  67     // default serial merge threshold depends on device type
  68     size_t default_serial_merge_threshold = 32768;
  69     if(device.type() & device::gpu) {
  70         default_serial_merge_threshold = 2048;
  71     }
  72
  73     // loading serial merge threshold parameter
  74     const size_t serial_merge_threshold =
  75         parameters->get(cache_key, "serial_merge_threshold",
  76                         static_cast<uint_>(default_serial_merge_threshold));
  77
  78     // choosing merge algorithm
  79     const size_t total_count =
  80         detail::iterator_range_size(first1, last1)
  81         + detail::iterator_range_size(first2, last2);
  82     // for small inputs serial merge turns out to outperform
  83     // merge with merge path algorithm
  84     if(total_count <= serial_merge_threshold){
  85        return detail::serial_merge(first1, last1, first2, last2, result, comp, queue);
  86     }
  87     return detail::merge_with_merge_path(first1, last1, first2, last2, result, comp, queue);
  88 }
  89
  90 /// \overload
  91 template<class InputIterator1, class InputIterator2, class OutputIterator>
  92 inline OutputIterator merge(InputIterator1 first1,
  93                             InputIterator1 last1,
  94                             InputIterator2 first2,
  95                             InputIterator2 last2,
  96                             OutputIterator result,
  97                             command_queue &queue = system::default_queue())
  98 {
  99     typedef typename std::iterator_traits<InputIterator1>::value_type value_type;
 100     less<value_type> less_than;
 101     return merge(first1, last1, first2, last2, result, less_than, queue);
 102 }
 103
 104 } // end compute namespace
 105 } // end boost namespace
 106
 107 #endif // BOOST_COMPUTE_ALGORITHM_MERGE_HPP