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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-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef _LIBCPP___ALGORITHM_SHIFT_RIGHT_H10#define _LIBCPP___ALGORITHM_SHIFT_RIGHT_H11 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_header21#endif22 23_LIBCPP_PUSH_MACROS24#include <__undef_macros>25 26_LIBCPP_BEGIN_NAMESPACE_STD27 28#if _LIBCPP_STD_VER >= 2029 30template <class _ForwardIterator>31inline _LIBCPP_HIDE_FROM_ABI constexpr _ForwardIterator32shift_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 bother68 // 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 >= 20100 101_LIBCPP_END_NAMESPACE_STD102 103_LIBCPP_POP_MACROS104 105#endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H106