1//===----------------------------------------------------------------------===//
 2//
 3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 4// See https://llvm.org/LICENSE.txt for license information.
 5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 6//
 7//===----------------------------------------------------------------------===//
 8
 9#ifndef _LIBCPP___ALGORITHM_RANGES_REVERSE_H
10#define _LIBCPP___ALGORITHM_RANGES_REVERSE_H
11
12#include <__config>
13#include <__iterator/concepts.h>
14#include <__iterator/iter_swap.h>
15#include <__iterator/next.h>
16#include <__iterator/permutable.h>
17#include <__ranges/access.h>
18#include <__ranges/concepts.h>
19#include <__ranges/dangling.h>
20
21#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
22#  pragma GCC system_header
23#endif
24
25#if _LIBCPP_STD_VER >= 20
26
27_LIBCPP_BEGIN_NAMESPACE_STD
28
29namespace ranges {
30struct __reverse {
31  template <bidirectional_iterator _Iter, sentinel_for<_Iter> _Sent>
32    requires permutable<_Iter>
33  _LIBCPP_HIDE_FROM_ABI constexpr _Iter operator()(_Iter __first, _Sent __last) const {
34    if constexpr (random_access_iterator<_Iter>) {
35      if (__first == __last)
36        return __first;
37
38      auto __end = ranges::next(__first, __last);
39      auto __ret = __end;
40
41      while (__first < --__end) {
42        ranges::iter_swap(__first, __end);
43        ++__first;
44      }
45      return __ret;
46    } else {
47      auto __end = ranges::next(__first, __last);
48      auto __ret = __end;
49
50      while (__first != __end) {
51        if (__first == --__end)
52          break;
53
54        ranges::iter_swap(__first, __end);
55        ++__first;
56      }
57      return __ret;
58    }
59  }
60
61  template <bidirectional_range _Range>
62    requires permutable<iterator_t<_Range>>
63  _LIBCPP_HIDE_FROM_ABI constexpr borrowed_iterator_t<_Range> operator()(_Range&& __range) const {
64    return (*this)(ranges::begin(__range), ranges::end(__range));
65  }
66};
67
68inline namespace __cpo {
69inline constexpr auto reverse = __reverse{};
70} // namespace __cpo
71} // namespace ranges
72
73_LIBCPP_END_NAMESPACE_STD
74
75#endif // _LIBCPP_STD_VER >= 20
76
77#endif // _LIBCPP___ALGORITHM_RANGES_REVERSE_H