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// SPDX-FileCopyrightText: Copyright © DUNE Project contributors, see file LICENSE.md in module root
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
#ifndef DUNE_COMMON_STD_ALGORITHM_HH
#define DUNE_COMMON_STD_ALGORITHM_HH
#include <version>
#if !(__cpp_impl_three_way_comparison >= 201907L && __cpp_lib_concepts && __has_include(<compare>))
#error "Three-way comparison requires language support!"
#endif
#include <algorithm>
#include <compare>
#include <type_traits>
#include <dune/common/std/compare.hh>
namespace Dune::Std {
/**
* \brief Lexicographically compares two ranges `[first1, last1)` and `[first2, last2)`
* using three-way comparison and produces a result of the strongest applicable
* comparison category type.
*
* Implementation taken from https://en.cppreference.com/w/cpp/algorithm/lexicographical_compare_three_way
*
* The standard implementation is available with libstdc++ >= 10 and libc++ >= 17
*/
#if __cpp_lib_three_way_comparison >= 201907L
using std::lexicographical_compare_three_way;
#else // __cpp_lib_three_way_comparison
template <class I1, class I2, class Cmp = Std::compare_three_way>
constexpr auto lexicographical_compare_three_way(I1 f1, I1 l1, I2 f2, I2 l2, Cmp comp = {})
-> decltype(comp(*f1, *f2))
{
using ret_t = decltype(comp(*f1, *f2));
static_assert(std::disjunction_v<
std::is_same<ret_t, std::strong_ordering>,
std::is_same<ret_t, std::weak_ordering>,
std::is_same<ret_t, std::partial_ordering>>,
"The return type must be a comparison category type.");
bool exhaust1 = (f1 == l1);
bool exhaust2 = (f2 == l2);
for (; !exhaust1 && !exhaust2; exhaust1 = (++f1 == l1), exhaust2 = (++f2 == l2))
if (auto c = comp(*f1, *f2); c != 0)
return c;
return !exhaust1 ? std::strong_ordering::greater:
!exhaust2 ? std::strong_ordering::less:
std::strong_ordering::equal;
}
#endif // __cpp_lib_three_way_comparison
} // end namespace Dune::Std
#endif // DUNE_COMMON_STD_ALGORITHM_HH
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