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_SHIFT_RIGHT_H
10#define _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
11
12#include <__algorithm/iterator_operations.h>
13#include <__algorithm/move.h>
14#include <__algorithm/move_backward.h>
15#include <__algorithm/swap_ranges.h>
16#include <__assert>
17#include <__concepts/derived_from.h>
18#include <__config>
19#include <__iterator/concepts.h>
20#include <__iterator/iterator_traits.h>
21#include <__utility/move.h>
22#include <__utility/pair.h>
23#include <__utility/swap.h>
24
25#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
26# pragma GCC system_header
27#endif
28
29_LIBCPP_PUSH_MACROS
30#include <__undef_macros>
31
32_LIBCPP_BEGIN_NAMESPACE_STD
33
34#if _LIBCPP_STD_VER >= 20
35
36template <class _AlgPolicy, class _Iter, class _Sent>
37_LIBCPP_HIDE_FROM_ABI constexpr pair<_Iter, _Iter>
38__shift_right(_Iter __first, _Sent __last, typename _IterOps<_AlgPolicy>::template __difference_type<_Iter> __n) {
39 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__n >= 0, "Providing a negative shift amount to shift_right is UB");
40 if (__n == 0) {
41 _Iter __end = _IterOps<_AlgPolicy>::next(__first, __last);
42 return pair<_Iter, _Iter>(std::move(__first), std::move(__end));
43 }
44
45 using _IterCategory = typename _IterOps<_AlgPolicy>::template __iterator_category<_Iter>;
46
47 if constexpr (derived_from<_IterCategory, random_access_iterator_tag>) {
48 _Iter __end = _IterOps<_AlgPolicy>::next(__first, __last);
49 auto __size = __end - __first;
50 if (__n >= __size) {
51 return pair<_Iter, _Iter>(__end, std::move(__end));
52 }
53 _Iter __m = __first;
54 _IterOps<_AlgPolicy>::advance(__m, (__size - __n));
55 auto __ret = std::__move_backward<_AlgPolicy>(std::move(__first), std::move(__m), __end);
56 return pair<_Iter, _Iter>(std::move(__ret.second), std::move(__end));
57 } else if constexpr (derived_from<_IterCategory, bidirectional_iterator_tag>) {
58 _Iter __end = _IterOps<_AlgPolicy>::next(__first, __last);
59 if constexpr (sized_sentinel_for<_Sent, _Iter>) {
60 if (__n >= ranges::distance(__first, __last)) {
61 return pair<_Iter, _Iter>(__end, std::move(__end));
62 }
63 }
64 _Iter __m = __end;
65 for (; __n > 0; --__n) {
66 if (__m == __first) {
67 return pair<_Iter, _Iter>(__end, std::move(__end));
68 }
69 --__m;
70 }
71 auto __ret = std::__move_backward<_AlgPolicy>(std::move(__first), std::move(__m), __end);
72 return pair<_Iter, _Iter>(std::move(__ret.second), std::move(__end));
73 } else {
74 _Iter __ret = __first;
75 for (; __n > 0; --__n) {
76 if (__ret == __last) {
77 return pair<_Iter, _Iter>(__ret, std::move(__ret));
78 }
79 ++__ret;
80 }
81
82 // We have an __n-element scratch space from __first to __ret.
83 // Slide an __n-element window [__trail, __lead) from left to right.
84 // We're essentially doing swap_ranges(__first, __ret, __trail, __lead)
85 // over and over; but once __lead reaches __end we needn't bother
86 // to save the values of elements [__trail, __end).
87
88 auto __trail = __first;
89 auto __lead = __ret;
90 while (__trail != __ret) {
91 if (__lead == __last) {
92 std::__move<_AlgPolicy>(std::move(__first), std::move(__trail), __ret);
93 return pair<_Iter, _Iter>(__ret, std::move(__lead));
94 }
95 ++__trail;
96 ++__lead;
97 }
98
99 _Iter __mid = __first;
100 while (true) {
101 if (__lead == __last) {
102 __trail = std::__move<_AlgPolicy>(__mid, __ret, __trail).second;
103 std::__move<_AlgPolicy>(std::move(__first), std::move(__mid), std::move(__trail));
104 return pair<_Iter, _Iter>(__ret, std::move(__lead));
105 }
106 _IterOps<_AlgPolicy>::iter_swap(__mid, __trail);
107 ++__mid;
108 ++__trail;
109 ++__lead;
110 if (__mid == __ret) {
111 __mid = __first;
112 }
113 }
114 }
115}
116
117template <class _ForwardIterator>
118_LIBCPP_HIDE_FROM_ABI constexpr _ForwardIterator
119shift_right(_ForwardIterator __first,
120 _ForwardIterator __last,
121 typename iterator_traits<_ForwardIterator>::difference_type __n) {
122 return std::__shift_right<_ClassicAlgPolicy>(std::move(__first), std::move(__last), __n).first;
123}
124
125#endif // _LIBCPP_STD_VER >= 20
126
127_LIBCPP_END_NAMESPACE_STD
128
129_LIBCPP_POP_MACROS
130
131#endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
132