//---------------------------------------------------------------------------//
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// Copyright (c) 2016 Jakub Szuppe <j.szuppe@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_ON_CPU_HPP
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#define BOOST_COMPUTE_ALGORITHM_DETAIL_FIND_EXTREMA_ON_CPU_HPP
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#include <algorithm>
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#include <boost/compute/algorithm/detail/find_extrema_with_reduce.hpp>
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#include <boost/compute/algorithm/detail/find_extrema_with_atomics.hpp>
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#include <boost/compute/algorithm/detail/serial_find_extrema.hpp>
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#include <boost/compute/detail/iterator_range_size.hpp>
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#include <boost/compute/iterator/buffer_iterator.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_on_cpu(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 input_type;
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typedef typename std::iterator_traits<InputIterator>::difference_type difference_type;
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size_t count = iterator_range_size(first, last);
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const device &device = queue.get_device();
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const uint_ compute_units = queue.get_device().compute_units();
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boost::shared_ptr<parameter_cache> parameters =
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detail::parameter_cache::get_global_cache(device);
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std::string cache_key =
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"__boost_find_extrema_cpu_"
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+ boost::lexical_cast<std::string>(sizeof(input_type));
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// for inputs smaller than serial_find_extrema_threshold
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// serial_find_extrema algorithm is used
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uint_ serial_find_extrema_threshold = parameters->get(
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cache_key,
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"serial_find_extrema_threshold",
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16384 * sizeof(input_type)
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);
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serial_find_extrema_threshold =
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(std::max)(serial_find_extrema_threshold, uint_(2 * compute_units));
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const context &context = queue.get_context();
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if(count < serial_find_extrema_threshold) {
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return serial_find_extrema(first, last, compare, find_minimum, queue);
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}
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meta_kernel k("find_extrema_on_cpu");
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buffer output(context, sizeof(input_type) * compute_units);
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buffer output_idx(
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context, sizeof(uint_) * compute_units,
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buffer::read_write | buffer::alloc_host_ptr
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);
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size_t count_arg = k.add_arg<uint_>("count");
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size_t output_arg =
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k.add_arg<input_type *>(memory_object::global_memory, "output");
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size_t output_idx_arg =
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k.add_arg<uint_ *>(memory_object::global_memory, "output_idx");
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k <<
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"uint block = " <<
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"(uint)ceil(((float)count)/get_global_size(0));\n" <<
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"uint index = get_global_id(0) * block;\n" <<
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"uint end = min(count, index + block);\n" <<
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"uint value_index = index;\n" <<
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k.decl<input_type>("value") << " = " << first[k.var<uint_>("index")] << ";\n" <<
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"index++;\n" <<
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"while(index < end){\n" <<
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k.decl<input_type>("candidate") <<
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" = " << first[k.var<uint_>("index")] << ";\n" <<
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"#ifndef BOOST_COMPUTE_FIND_MAXIMUM\n" <<
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"bool compare = " << compare(k.var<input_type>("candidate"),
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k.var<input_type>("value")) << ";\n" <<
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"#else\n" <<
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"bool compare = " << compare(k.var<input_type>("value"),
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k.var<input_type>("candidate")) << ";\n" <<
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"#endif\n" <<
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"value = compare ? candidate : value;\n" <<
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"value_index = compare ? index : value_index;\n" <<
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"index++;\n" <<
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"}\n" <<
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"output[get_global_id(0)] = value;\n" <<
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"output_idx[get_global_id(0)] = value_index;\n";
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size_t global_work_size = compute_units;
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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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kernel.set_arg(count_arg, static_cast<uint_>(count));
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kernel.set_arg(output_arg, output);
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kernel.set_arg(output_idx_arg, output_idx);
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queue.enqueue_1d_range_kernel(kernel, 0, global_work_size, 0);
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buffer_iterator<input_type> result = serial_find_extrema(
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make_buffer_iterator<input_type>(output),
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make_buffer_iterator<input_type>(output, global_work_size),
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compare,
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find_minimum,
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queue
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);
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uint_* output_idx_host_ptr =
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static_cast<uint_*>(
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queue.enqueue_map_buffer(
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output_idx, command_queue::map_read,
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0, global_work_size * sizeof(uint_)
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)
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);
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difference_type extremum_idx =
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static_cast<difference_type>(*(output_idx_host_ptr + result.get_index()));
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return first + extremum_idx;
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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_ON_CPU_HPP
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