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/move.h>
13#include <__algorithm/move_backward.h>
14#include <__algorithm/swap_ranges.h>
15#include <__config>
16#include <__iterator/iterator_traits.h>
17#include <__utility/swap.h>
18
19#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
20# pragma GCC system_header
21#endif
22
23_LIBCPP_PUSH_MACROS
24#include <__undef_macros>
25
26_LIBCPP_BEGIN_NAMESPACE_STD
27
28#if _LIBCPP_STD_VER >= 20
29
30template <class _ForwardIterator>
31inline _LIBCPP_HIDE_FROM_ABI constexpr _ForwardIterator
32shift_right(_ForwardIterator __first,
33 _ForwardIterator __last,
34 typename iterator_traits<_ForwardIterator>::difference_type __n) {
35 if (__n == 0) {
36 return __first;
37 }
38
39 if constexpr (__has_random_access_iterator_category<_ForwardIterator>::value) {
40 decltype(__n) __d = __last - __first;
41 if (__n >= __d) {
42 return __last;
43 }
44 _ForwardIterator __m = __first + (__d - __n);
45 return std::move_backward(__first, __m, __last);
46 } else if constexpr (__has_bidirectional_iterator_category<_ForwardIterator>::value) {
47 _ForwardIterator __m = __last;
48 for (; __n > 0; --__n) {
49 if (__m == __first) {
50 return __last;
51 }
52 --__m;
53 }
54 return std::move_backward(__first, __m, __last);
55 } else {
56 _ForwardIterator __ret = __first;
57 for (; __n > 0; --__n) {
58 if (__ret == __last) {
59 return __last;
60 }
61 ++__ret;
62 }
63
64 // We have an __n-element scratch space from __first to __ret.
65 // Slide an __n-element window [__trail, __lead) from left to right.
66 // We're essentially doing swap_ranges(__first, __ret, __trail, __lead)
67 // over and over; but once __lead reaches __last we needn't bother
68 // to save the values of elements [__trail, __last).
69
70 auto __trail = __first;
71 auto __lead = __ret;
72 while (__trail != __ret) {
73 if (__lead == __last) {
74 std::move(__first, __trail, __ret);
75 return __ret;
76 }
77 ++__trail;
78 ++__lead;
79 }
80
81 _ForwardIterator __mid = __first;
82 while (true) {
83 if (__lead == __last) {
84 __trail = std::move(__mid, __ret, __trail);
85 std::move(__first, __mid, __trail);
86 return __ret;
87 }
88 swap(*__mid, *__trail);
89 ++__mid;
90 ++__trail;
91 ++__lead;
92 if (__mid == __ret) {
93 __mid = __first;
94 }
95 }
96 }
97}
98
99#endif // _LIBCPP_STD_VER >= 20
100
101_LIBCPP_END_NAMESPACE_STD
102
103_LIBCPP_POP_MACROS
104
105#endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
106