parallel_algorithms.h

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// SPDX-License-Identifier: AGPL-3.0-only
// Copyright (C) 2026 Artificial Intelligence Techniques, S.L. and Roberto López González
 
#pragma once
#ifndef OPENNN_PARALLEL_ALGORITHMS_H_
#define OPENNN_PARALLEL_ALGORITHMS_H_
 
#include "opennn/core/opennn_types.h"
 
#if defined(OPENNN_HAS_PARALLEL_ALGORITHMS)
#include <execution>
#endif
 
#if defined(_OPENMP)
#include <omp.h>
#endif
 
namespace opennn
{
 
inline constexpr ptrdiff_t parallel_algorithm_min_size = 65536;
 
inline bool use_parallel_algorithm(ptrdiff_t size) noexcept
{
    if (size < parallel_algorithm_min_size) return false;
#if defined(_OPENMP)
    if (omp_in_parallel()) return false;
#endif
    return true;
}
 
template<typename Iterator, typename Compare = less<>>
void sort_parallel_if_large(Iterator first, Iterator last, Compare compare = {})
{
#if defined(OPENNN_HAS_PARALLEL_ALGORITHMS) && defined(__cpp_lib_parallel_algorithm)
    if (use_parallel_algorithm(last - first))
        sort(execution::par, first, last, compare);
    else
#endif
        sort(first, last, compare);
}
 
template<typename Iterator, typename Compare = less<>>
void stable_sort_parallel_if_large(Iterator first, Iterator last, Compare compare = {})
{
#if defined(OPENNN_HAS_PARALLEL_ALGORITHMS) && defined(__cpp_lib_parallel_algorithm)
    if (use_parallel_algorithm(last - first))
        stable_sort(execution::par, first, last, compare);
    else
#endif
        stable_sort(first, last, compare);
}
 
template<typename Iterator, typename Compare = less<>>
void nth_element_parallel_if_large(Iterator first, Iterator nth, Iterator last,
                                   Compare compare = {})
{
#if defined(OPENNN_HAS_PARALLEL_ALGORITHMS) && defined(__cpp_lib_parallel_algorithm)
    if (use_parallel_algorithm(last - first))
        nth_element(execution::par, first, nth, last, compare);
    else
#endif
        nth_element(first, nth, last, compare);
}
 
}
 
#endif