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+//---------------------------------------------------------------------------//
+// Copyright (c) 2013-2014 Kyle Lutz <kyle.r.lutz@gmail.com>
+//
+// Distributed under the Boost Software License, Version 1.0
+// See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt
+//
+// See http://boostorg.github.com/compute for more information.
+//---------------------------------------------------------------------------//
+
+#ifndef BOOST_COMPUTE_ALGORITHM_ADJACENT_FIND_HPP
+#define BOOST_COMPUTE_ALGORITHM_ADJACENT_FIND_HPP
+
+#include <iterator>
+
+#include <boost/compute/command_queue.hpp>
+#include <boost/compute/lambda.hpp>
+#include <boost/compute/system.hpp>
+#include <boost/compute/container/detail/scalar.hpp>
+#include <boost/compute/detail/iterator_range_size.hpp>
+#include <boost/compute/detail/meta_kernel.hpp>
+#include <boost/compute/functional/operator.hpp>
+#include <boost/compute/type_traits/vector_size.hpp>
+
+namespace boost {
+namespace compute {
+namespace detail {
+
+template<class InputIterator, class Compare>
+inline InputIterator
+serial_adjacent_find(InputIterator first,
+ InputIterator last,
+ Compare compare,
+ command_queue &queue)
+{
+ if(first == last){
+ return last;
+ }
+
+ const context &context = queue.get_context();
+
+ detail::scalar<uint_> output(context);
+
+ detail::meta_kernel k("serial_adjacent_find");
+
+ size_t size_arg = k.add_arg<const uint_>("size");
+ size_t output_arg = k.add_arg<uint_ *>(memory_object::global_memory, "output");
+
+ k << k.decl<uint_>("result") << " = size;\n"
+ << "for(uint i = 0; i < size - 1; i++){\n"
+ << " if(" << compare(first[k.expr<uint_>("i")],
+ first[k.expr<uint_>("i+1")]) << "){\n"
+ << " result = i;\n"
+ << " break;\n"
+ << " }\n"
+ << "}\n"
+ << "*output = result;\n";
+
+ k.set_arg<const uint_>(
+ size_arg, static_cast<uint_>(detail::iterator_range_size(first, last))
+ );
+ k.set_arg(output_arg, output.get_buffer());
+
+ k.exec_1d(queue, 0, 1, 1);
+
+ return first + output.read(queue);
+}
+
+template<class InputIterator, class Compare>
+inline InputIterator
+adjacent_find_with_atomics(InputIterator first,
+ InputIterator last,
+ Compare compare,
+ command_queue &queue)
+{
+ if(first == last){
+ return last;
+ }
+
+ const context &context = queue.get_context();
+ size_t count = detail::iterator_range_size(first, last);
+
+ // initialize output to the last index
+ detail::scalar<uint_> output(context);
+ output.write(static_cast<uint_>(count), queue);
+
+ detail::meta_kernel k("adjacent_find_with_atomics");
+
+ size_t output_arg = k.add_arg<uint_ *>(memory_object::global_memory, "output");
+
+ k << "const uint i = get_global_id(0);\n"
+ << "if(" << compare(first[k.expr<uint_>("i")],
+ first[k.expr<uint_>("i+1")]) << "){\n"
+ << " atomic_min(output, i);\n"
+ << "}\n";
+
+ k.set_arg(output_arg, output.get_buffer());
+
+ k.exec_1d(queue, 0, count - 1, 1);
+
+ return first + output.read(queue);
+}
+
+} // end detail namespace
+
+/// Searches the range [\p first, \p last) for two identical adjacent
+/// elements and returns an iterator pointing to the first.
+///
+/// \param first first element in the range to search
+/// \param last last element in the range to search
+/// \param compare binary comparison function
+/// \param queue command queue to perform the operation
+///
+/// \return \c InputIteratorm to the first element which compares equal
+/// to the following element. If none are equal, returns \c last.
+///
+/// \see find(), adjacent_difference()
+template<class InputIterator, class Compare>
+inline InputIterator
+adjacent_find(InputIterator first,
+ InputIterator last,
+ Compare compare,
+ command_queue &queue = system::default_queue())
+{
+ size_t count = detail::iterator_range_size(first, last);
+ if(count < 32){
+ return detail::serial_adjacent_find(first, last, compare, queue);
+ }
+ else {
+ return detail::adjacent_find_with_atomics(first, last, compare, queue);
+ }
+}
+
+/// \overload
+template<class InputIterator>
+inline InputIterator
+adjacent_find(InputIterator first,
+ InputIterator last,
+ command_queue &queue = system::default_queue())
+{
+ typedef typename std::iterator_traits<InputIterator>::value_type value_type;
+
+ using ::boost::compute::lambda::_1;
+ using ::boost::compute::lambda::_2;
+ using ::boost::compute::lambda::all;
+
+ if(vector_size<value_type>::value == 1){
+ return ::boost::compute::adjacent_find(
+ first, last, _1 == _2, queue
+ );
+ }
+ else {
+ return ::boost::compute::adjacent_find(
+ first, last, all(_1 == _2), queue
+ );
+ }
+}
+
+} // end compute namespace
+} // end boost namespace
+
+#endif // BOOST_COMPUTE_ALGORITHM_ADJACENT_FIND_HPP