| Yi Kong | 878f994 | 2023-12-13 12:55:04 +0900 | [diff] [blame^] | 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_BEGIN_NAMESPACE_STD |
| 24 | |
| 25 | #if _LIBCPP_STD_VER >= 20 |
| 26 | |
| 27 | template <class _ForwardIterator> |
| 28 | inline _LIBCPP_INLINE_VISIBILITY constexpr |
| 29 | _ForwardIterator |
| 30 | shift_right(_ForwardIterator __first, _ForwardIterator __last, |
| 31 | typename iterator_traits<_ForwardIterator>::difference_type __n) |
| 32 | { |
| 33 | if (__n == 0) { |
| 34 | return __first; |
| 35 | } |
| 36 | |
| 37 | if constexpr (__has_random_access_iterator_category<_ForwardIterator>::value) { |
| 38 | decltype(__n) __d = __last - __first; |
| 39 | if (__n >= __d) { |
| 40 | return __last; |
| 41 | } |
| 42 | _ForwardIterator __m = __first + (__d - __n); |
| 43 | return _VSTD::move_backward(__first, __m, __last); |
| 44 | } else if constexpr (__has_bidirectional_iterator_category<_ForwardIterator>::value) { |
| 45 | _ForwardIterator __m = __last; |
| 46 | for (; __n > 0; --__n) { |
| 47 | if (__m == __first) { |
| 48 | return __last; |
| 49 | } |
| 50 | --__m; |
| 51 | } |
| 52 | return _VSTD::move_backward(__first, __m, __last); |
| 53 | } else { |
| 54 | _ForwardIterator __ret = __first; |
| 55 | for (; __n > 0; --__n) { |
| 56 | if (__ret == __last) { |
| 57 | return __last; |
| 58 | } |
| 59 | ++__ret; |
| 60 | } |
| 61 | |
| 62 | // We have an __n-element scratch space from __first to __ret. |
| 63 | // Slide an __n-element window [__trail, __lead) from left to right. |
| 64 | // We're essentially doing swap_ranges(__first, __ret, __trail, __lead) |
| 65 | // over and over; but once __lead reaches __last we needn't bother |
| 66 | // to save the values of elements [__trail, __last). |
| 67 | |
| 68 | auto __trail = __first; |
| 69 | auto __lead = __ret; |
| 70 | while (__trail != __ret) { |
| 71 | if (__lead == __last) { |
| 72 | _VSTD::move(__first, __trail, __ret); |
| 73 | return __ret; |
| 74 | } |
| 75 | ++__trail; |
| 76 | ++__lead; |
| 77 | } |
| 78 | |
| 79 | _ForwardIterator __mid = __first; |
| 80 | while (true) { |
| 81 | if (__lead == __last) { |
| 82 | __trail = _VSTD::move(__mid, __ret, __trail); |
| 83 | _VSTD::move(__first, __mid, __trail); |
| 84 | return __ret; |
| 85 | } |
| 86 | swap(*__mid, *__trail); |
| 87 | ++__mid; |
| 88 | ++__trail; |
| 89 | ++__lead; |
| 90 | if (__mid == __ret) { |
| 91 | __mid = __first; |
| 92 | } |
| 93 | } |
| 94 | } |
| 95 | } |
| 96 | |
| 97 | #endif // _LIBCPP_STD_VER >= 20 |
| 98 | |
| 99 | _LIBCPP_END_NAMESPACE_STD |
| 100 | |
| 101 | #endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H |