//---------------------------------------------------------------------------//
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// Copyright (c) 2013 Kyle Lutz <kyle.r.lutz@gmail.com>
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//
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// Distributed under the Boost Software License, Version 1.0
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// See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt
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//
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// See http://boostorg.github.com/compute for more information.
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//---------------------------------------------------------------------------//
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#ifndef BOOST_COMPUTE_ALGORITHM_DETAIL_FIND_EXTREMA_WITH_ATOMICS_HPP
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#define BOOST_COMPUTE_ALGORITHM_DETAIL_FIND_EXTREMA_WITH_ATOMICS_HPP
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#include <boost/compute/types.hpp>
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#include <boost/compute/command_queue.hpp>
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#include <boost/compute/container/detail/scalar.hpp>
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#include <boost/compute/functional/atomic.hpp>
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#include <boost/compute/detail/meta_kernel.hpp>
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#include <boost/compute/detail/iterator_range_size.hpp>
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namespace boost {
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namespace compute {
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namespace detail {
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template<class InputIterator, class Compare>
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inline InputIterator find_extrema_with_atomics(InputIterator first,
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InputIterator last,
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Compare compare,
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const bool find_minimum,
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command_queue &queue)
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{
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typedef typename std::iterator_traits<InputIterator>::value_type value_type;
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typedef typename std::iterator_traits<InputIterator>::difference_type difference_type;
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const context &context = queue.get_context();
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meta_kernel k("find_extrema");
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atomic_cmpxchg<uint_> atomic_cmpxchg_uint;
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k <<
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"const uint gid = get_global_id(0);\n" <<
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"uint old_index = *index;\n" <<
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k.decl<value_type>("old") <<
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" = " << first[k.var<uint_>("old_index")] << ";\n" <<
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k.decl<value_type>("new") <<
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" = " << first[k.var<uint_>("gid")] << ";\n" <<
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k.decl<bool>("compare_result") << ";\n" <<
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"#ifdef BOOST_COMPUTE_FIND_MAXIMUM\n" <<
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"while(" <<
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"(compare_result = " << compare(k.var<value_type>("old"),
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k.var<value_type>("new")) << ")" <<
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" || (!(compare_result" <<
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" || " << compare(k.var<value_type>("new"),
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k.var<value_type>("old")) << ") "
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"&& gid < old_index)){\n" <<
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"#else\n" <<
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// while condition explained for minimum case with less (<)
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// as comparison function:
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// while(new_value < old_value
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// OR (new_value == old_value AND new_index < old_index))
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"while(" <<
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"(compare_result = " << compare(k.var<value_type>("new"),
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k.var<value_type>("old")) << ")" <<
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" || (!(compare_result" <<
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" || " << compare(k.var<value_type>("old"),
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k.var<value_type>("new")) << ") "
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"&& gid < old_index)){\n" <<
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"#endif\n" <<
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" if(" << atomic_cmpxchg_uint(k.var<uint_ *>("index"),
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k.var<uint_>("old_index"),
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k.var<uint_>("gid")) << " == old_index)\n" <<
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" break;\n" <<
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" else\n" <<
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" old_index = *index;\n" <<
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"old = " << first[k.var<uint_>("old_index")] << ";\n" <<
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"}\n";
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size_t index_arg_index = k.add_arg<uint_ *>(memory_object::global_memory, "index");
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std::string options;
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if(!find_minimum){
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options = "-DBOOST_COMPUTE_FIND_MAXIMUM";
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}
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kernel kernel = k.compile(context, options);
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// setup index buffer
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scalar<uint_> index(context);
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kernel.set_arg(index_arg_index, index.get_buffer());
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// initialize index
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index.write(0, queue);
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// run kernel
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size_t count = iterator_range_size(first, last);
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queue.enqueue_1d_range_kernel(kernel, 0, count, 0);
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// read index and return iterator
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return first + static_cast<difference_type>(index.read(queue));
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}
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} // end detail namespace
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} // end compute namespace
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} // end boost namespace
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#endif // BOOST_COMPUTE_ALGORITHM_DETAIL_FIND_EXTREMA_WITH_ATOMICS_HPP
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