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 #include <type_traits> 19 20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 21 # pragma GCC system_header 22 # pragma clang include_instead(<algorithm>) 23 #endif 24 25 _LIBCPP_BEGIN_NAMESPACE_STD 26 27 #if _LIBCPP_STD_VER > 17 28 29 template <class _ForwardIterator> 30 inline _LIBCPP_INLINE_VISIBILITY constexpr 31 _ForwardIterator 32 shift_right(_ForwardIterator __first, _ForwardIterator __last, 33 typename iterator_traits<_ForwardIterator>::difference_type __n) 34 { 35 if (__n == 0) { 36 return __first; 37 } 38 39 if constexpr (__is_cpp17_random_access_iterator<_ForwardIterator>::value) { 40 decltype(__n) __d = __last - __first; 41 if (__n >= __d) { 42 return __last; 43 } 44 _ForwardIterator __m = __first + (__d - __n); 45 return _VSTD::move_backward(__first, __m, __last); 46 } else if constexpr (__is_cpp17_bidirectional_iterator<_ForwardIterator>::value) { 47 _ForwardIterator __m = __last; 48 for (; __n > 0; --__n) { 49 if (__m == __first) { 50 return __last; 51 } 52 --__m; 53 } 54 return _VSTD::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 _VSTD::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 = _VSTD::move(__mid, __ret, __trail); 85 _VSTD::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 > 17 100 101 _LIBCPP_END_NAMESPACE_STD 102 103 #endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H 104