boost::compute::merge
// In header: <boost/compute/algorithm/merge.hpp> template<typename InputIterator1, typename InputIterator2, typename OutputIterator, typename Compare> OutputIterator merge(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp, command_queue & queue = system::default_queue());