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