--- /dev/null
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ALGORITHM_RANGES_MAX_ELEMENT_H
+#define _LIBCPP___ALGORITHM_RANGES_MAX_ELEMENT_H
+
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
+#include <__functional/ranges_operations.h>
+#include <__iterator/concepts.h>
+#include <__iterator/projected.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/dangling.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_CONCEPTS) && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+namespace __max_element {
+struct __fn {
+ template <class _Ip, class _Sp, class _Proj, class _Comp>
+ _LIBCPP_HIDE_FROM_ABI static constexpr
+ _Ip __go(_Ip __first, _Sp __last, _Comp& __comp, _Proj& __proj) {
+ if (__first == __last)
+ return __first;
+
+ _Ip __i = __first;
+ while (++__i != __last)
+ if (std::invoke(__comp, std::invoke(__proj, *__first), std::invoke(__proj, *__i)))
+ __first = __i;
+ return __first;
+ }
+
+ template <forward_iterator _Ip, sentinel_for<_Ip> _Sp, class _Proj = identity,
+ indirect_strict_weak_order<projected<_Ip, _Proj>> _Comp = ranges::less>
+ _LIBCPP_HIDE_FROM_ABI constexpr
+ _Ip operator()(_Ip __first, _Sp __last, _Comp __comp = {}, _Proj __proj = {}) const {
+ return __go(__first, __last, __comp, __proj);
+ }
+
+ template <forward_range _Rp, class _Proj = identity,
+ indirect_strict_weak_order<projected<iterator_t<_Rp>, _Proj>> _Comp = ranges::less>
+ _LIBCPP_HIDE_FROM_ABI constexpr
+ borrowed_iterator_t<_Rp> operator()(_Rp&& __r, _Comp __comp = {}, _Proj __proj = {}) const {
+ return __go(ranges::begin(__r), ranges::end(__r), __comp, __proj);
+ }
+};
+} // namespace __max_element
+
+inline namespace __cpo {
+ inline constexpr auto max_element = __max_element::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_CONCEPTS) && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+#endif // _LIBCPP___ALGORITHM_RANGES_MAX_ELEMENT_H
--- /dev/null
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: libcpp-has-no-incomplete-ranges
+
+// template<forward_iterator I, sentinel_for<I> S, class Proj = identity,
+// indirect_strict_weak_order<projected<I, Proj>> Comp = ranges::less>
+// constexpr I ranges::max_element(I first, S last, Comp comp = {}, Proj proj = {});
+//
+// template<forward_range R, class Proj = identity,
+// indirect_strict_weak_order<projected<iterator_t<R>, Proj>> Comp = ranges::less>
+// constexpr borrowed_iterator_t<R> ranges::max_element(R&& r, Comp comp = {}, Proj proj = {});
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <random>
+#include <ranges>
+
+#include "test_macros.h"
+#include "test_iterators.h"
+
+template <class T>
+concept HasMaxElement = requires (T t) { std::ranges::max_element(t); };
+
+struct NoLessThanOp {};
+struct NotTotallyOrdered {
+ int i;
+ bool operator<(const NotTotallyOrdered& o) const { return i < o.i; }
+};
+
+static_assert(HasMaxElement<std::array<int, 0>>);
+static_assert(!HasMaxElement<int>);
+static_assert(!HasMaxElement<NoLessThanOp>);
+static_assert(!HasMaxElement<NotTotallyOrdered>);
+
+template <class Iter>
+constexpr void test_iterators(Iter first, Iter last) {
+ std::same_as<Iter> auto it = std::ranges::max_element(first, last);
+ if (first != last) {
+ for (Iter j = first; j != last; ++j)
+ assert(!(*j > *it));
+ } else {
+ assert(it == first);
+ }
+}
+
+template <class Range, class Iter>
+constexpr void test_range(Range&& rng, Iter begin, Iter end) {
+ std::same_as<Iter> auto it = std::ranges::max_element(std::forward<Range>(rng));
+ if (begin != end) {
+ for (Iter j = begin; j != end; ++j)
+ assert(!(*j > *it));
+ } else {
+ assert(it == begin);
+ }
+}
+
+template <class It>
+constexpr void test(std::initializer_list<int> a, int expected) {
+ const int* first = a.begin();
+ const int* last = a.end();
+ {
+ std::same_as<It> auto it = std::ranges::max_element(It(first), It(last));
+ assert(base(it) == first + expected);
+ }
+ {
+ using Sent = sentinel_wrapper<It>;
+ std::same_as<It> auto it = std::ranges::max_element(It(first), Sent(It(last)));
+ assert(base(it) == first + expected);
+ }
+ {
+ auto range = std::ranges::subrange(It(first), It(last));
+ std::same_as<It> auto it = std::ranges::max_element(range);
+ assert(base(it) == first + expected);
+ }
+ {
+ using Sent = sentinel_wrapper<It>;
+ auto range = std::ranges::subrange(It(first), Sent(It(last)));
+ std::same_as<It> auto it = std::ranges::max_element(range);
+ assert(base(it) == first + expected);
+ }
+}
+
+template <class It>
+constexpr bool test() {
+ test<It>({}, 0);
+ test<It>({1}, 0);
+ test<It>({1, 2}, 1);
+ test<It>({2, 1}, 0);
+ test<It>({2, 1, 2}, 0);
+ test<It>({2, 1, 1}, 0);
+
+ return true;
+}
+
+constexpr void test_borrowed_range_and_sentinel() {
+ int a[] = {7, 6, 1, 3, 5, 1, 2, 4};
+
+ int* ret = std::ranges::max_element(std::views::all(a));
+ assert(ret == a + 0);
+ assert(*ret == 7);
+}
+
+constexpr void test_comparator() {
+ int a[] = {7, 6, 9, 3, 5, 1, 2, 4};
+ int* ret = std::ranges::max_element(a, std::ranges::greater{});
+ assert(ret == a + 5);
+ assert(*ret == 1);
+}
+
+constexpr void test_projection() {
+ int a[] = {7, 6, 9, 3, 5, 1, 2, 4};
+ {
+ int* ret = std::ranges::max_element(a, std::ranges::less{}, [](int i) { return i == 5 ? 100 : i; });
+ assert(ret == a + 4);
+ assert(*ret == 5);
+ }
+ {
+ int* ret = std::ranges::max_element(a, std::less<int*>{}, [](int& i) { return &i; });
+ assert(ret == a + 7);
+ assert(*ret == 4);
+ }
+}
+
+struct Immobile {
+ int i;
+
+ constexpr Immobile(int i_) : i(i_) {}
+ Immobile(const Immobile&) = delete;
+ Immobile(Immobile&&) = delete;
+
+ auto operator<=>(const Immobile&) const = default;
+};
+
+constexpr void test_immobile() {
+
+ Immobile arr[] {1, 2, 3};
+ assert(std::ranges::max_element(arr) == arr);
+ assert(std::ranges::max_element(arr, arr + 3) == arr);
+}
+
+constexpr void test_dangling() {
+ int compares = 0;
+ int projections = 0;
+ auto comparator = [&](int a, int b) {
+ ++compares;
+ return a < b;
+ };
+ auto projection = [&](int a) {
+ ++projections;
+ return a;
+ };
+ [[maybe_unused]] std::same_as<std::ranges::dangling> auto ret =
+ std::ranges::max_element(std::array{1, 2, 3}, comparator, projection);
+ assert(compares == 2);
+ assert(projections == 4);
+}
+
+constexpr bool test() {
+
+ test<forward_iterator<const int*>>();
+ test<bidirectional_iterator<const int*>>();
+ test<random_access_iterator<const int*>>();
+ test<const int*>();
+
+ int a[] = {7, 6, 5, 3, 4, 2, 1, 8};
+ test_iterators(a, a + 8);
+ int a2[] = {7, 6, 5, 3, 4, 2, 1, 8};
+ test_range(a2, a2, a2 + 8);
+
+ test_borrowed_range_and_sentinel();
+ test_comparator();
+ test_projection();
+ test_dangling();
+
+ return true;
+}
+
+int main(int, char**) {
+ test();
+ static_assert(test());
+
+ return 0;
+}