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 
29 namespace ranges {
30 namespace __reverse {
31 struct __fn {
32   template <bidirectional_iterator _Iter, sentinel_for<_Iter> _Sent>
33     requires permutable<_Iter>
operator__fn34   _LIBCPP_HIDE_FROM_ABI constexpr _Iter operator()(_Iter __first, _Sent __last) const {
35     if constexpr (random_access_iterator<_Iter>) {
36       if (__first == __last)
37         return __first;
38 
39       auto __end = ranges::next(__first, __last);
40       auto __ret = __end;
41 
42       while (__first < --__end) {
43         ranges::iter_swap(__first, __end);
44         ++__first;
45       }
46       return __ret;
47     } else {
48       auto __end = ranges::next(__first, __last);
49       auto __ret = __end;
50 
51       while (__first != __end) {
52         if (__first == --__end)
53           break;
54 
55         ranges::iter_swap(__first, __end);
56         ++__first;
57       }
58       return __ret;
59     }
60   }
61 
62   template <bidirectional_range _Range>
63     requires permutable<iterator_t<_Range>>
operator__fn64   _LIBCPP_HIDE_FROM_ABI constexpr borrowed_iterator_t<_Range> operator()(_Range&& __range) const {
65     return (*this)(ranges::begin(__range), ranges::end(__range));
66   }
67 };
68 } // namespace __reverse
69 
70 inline namespace __cpo {
71 inline constexpr auto reverse = __reverse::__fn{};
72 } // namespace __cpo
73 } // namespace ranges
74 
75 _LIBCPP_END_NAMESPACE_STD
76 
77 #endif // _LIBCPP_STD_VER >= 20
78 
79 #endif // _LIBCPP___ALGORITHM_RANGES_REVERSE_H
80