ceph/src/boost/libs/compute/include/boost/compute/algorithm/detail/find_extrema_with_atomics.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_DETAIL_FIND_EXTREMA_WITH_ATOMICS_HPP
  12 #define BOOST_COMPUTE_ALGORITHM_DETAIL_FIND_EXTREMA_WITH_ATOMICS_HPP
  13
  14 #include <boost/compute/types.hpp>
  15 #include <boost/compute/command_queue.hpp>
  16 #include <boost/compute/container/detail/scalar.hpp>
  17 #include <boost/compute/functional/atomic.hpp>
  18 #include <boost/compute/detail/meta_kernel.hpp>
  19 #include <boost/compute/detail/iterator_range_size.hpp>
  20
  21 namespace boost {
  22 namespace compute {
  23 namespace detail {
  24
  25 template<class InputIterator, class Compare>
  26 inline InputIterator find_extrema_with_atomics(InputIterator first,
  27                                                InputIterator last,
  28                                                Compare compare,
  29                                                const bool find_minimum,
  30                                                command_queue &queue)
  31 {
  32     typedef typename std::iterator_traits<InputIterator>::value_type value_type;
  33     typedef typename std::iterator_traits<InputIterator>::difference_type difference_type;
  34
  35     const context &context = queue.get_context();
  36
  37     meta_kernel k("find_extrema");
  38     atomic_cmpxchg<uint_> atomic_cmpxchg_uint;
  39
  40     k <<
  41         "const uint gid = get_global_id(0);\n" <<
  42         "uint old_index = *index;\n" <<
  43
  44         k.decl<value_type>("old") <<
  45             " = " << first[k.var<uint_>("old_index")] << ";\n" <<
  46         k.decl<value_type>("new") <<
  47             " = " << first[k.var<uint_>("gid")] << ";\n" <<
  48
  49         k.decl<bool>("compare_result") << ";\n" <<
  50         "#ifdef BOOST_COMPUTE_FIND_MAXIMUM\n" <<
  51         "while(" <<
  52             "(compare_result = " << compare(k.var<value_type>("old"),
  53                                             k.var<value_type>("new")) << ")" <<
  54             " || (!(compare_result" <<
  55                       " || " << compare(k.var<value_type>("new"),
  56                                         k.var<value_type>("old")) << ") "
  57                   "&& gid < old_index)){\n" <<
  58         "#else\n" <<
  59         // while condition explained for minimum case with less (<)
  60         // as comparison function:
  61         // while(new_value < old_value
  62         //       OR (new_value == old_value AND new_index < old_index))
  63         "while(" <<
  64             "(compare_result = " << compare(k.var<value_type>("new"),
  65                                             k.var<value_type>("old"))  << ")" <<
  66             " || (!(compare_result" <<
  67                       " || " << compare(k.var<value_type>("old"),
  68                                         k.var<value_type>("new")) << ") "
  69                   "&& gid < old_index)){\n" <<
  70         "#endif\n" <<
  71
  72         "  if(" << atomic_cmpxchg_uint(k.var<uint_ *>("index"),
  73                                        k.var<uint_>("old_index"),
  74                                        k.var<uint_>("gid")) << " == old_index)\n" <<
  75         "      break;\n" <<
  76         "  else\n" <<
  77         "    old_index = *index;\n" <<
  78         "old = " << first[k.var<uint_>("old_index")] << ";\n" <<
  79         "}\n";
  80
  81     size_t index_arg_index = k.add_arg<uint_ *>(memory_object::global_memory, "index");
  82
  83     std::string options;
  84     if(!find_minimum){
  85         options = "-DBOOST_COMPUTE_FIND_MAXIMUM";
  86     }
  87     kernel kernel = k.compile(context, options);
  88
  89     // setup index buffer
  90     scalar<uint_> index(context);
  91     kernel.set_arg(index_arg_index, index.get_buffer());
  92
  93     // initialize index
  94     index.write(0, queue);
  95
  96     // run kernel
  97     size_t count = iterator_range_size(first, last);
  98     queue.enqueue_1d_range_kernel(kernel, 0, count, 0);
  99
 100     // read index and return iterator
 101     return first + static_cast<difference_type>(index.read(queue));
 102 }
 103
 104 } // end detail namespace
 105 } // end compute namespace
 106 } // end boost namespace
 107
 108 #endif // BOOST_COMPUTE_ALGORITHM_DETAIL_FIND_EXTREMA_WITH_ATOMICS_HPP