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 #endif 23 24 _LIBCPP_BEGIN_NAMESPACE_STD 25 26 #if _LIBCPP_STD_VER > 17 27 28 template <class _ForwardIterator> 29 inline _LIBCPP_INLINE_VISIBILITY constexpr 30 _ForwardIterator 31 shift_right(_ForwardIterator __first, _ForwardIterator __last, 32 typename iterator_traits<_ForwardIterator>::difference_type __n) 33 { 34 if (__n == 0) { 35 return __first; 36 } 37 38 if constexpr (__is_cpp17_random_access_iterator<_ForwardIterator>::value) { 39 decltype(__n) __d = __last - __first; 40 if (__n >= __d) { 41 return __last; 42 } 43 _ForwardIterator __m = __first + (__d - __n); 44 return _VSTD::move_backward(__first, __m, __last); 45 } else if constexpr (__is_cpp17_bidirectional_iterator<_ForwardIterator>::value) { 46 _ForwardIterator __m = __last; 47 for (; __n > 0; --__n) { 48 if (__m == __first) { 49 return __last; 50 } 51 --__m; 52 } 53 return _VSTD::move_backward(__first, __m, __last); 54 } else { 55 _ForwardIterator __ret = __first; 56 for (; __n > 0; --__n) { 57 if (__ret == __last) { 58 return __last; 59 } 60 ++__ret; 61 } 62 63 // We have an __n-element scratch space from __first to __ret. 64 // Slide an __n-element window [__trail, __lead) from left to right. 65 // We're essentially doing swap_ranges(__first, __ret, __trail, __lead) 66 // over and over; but once __lead reaches __last we needn't bother 67 // to save the values of elements [__trail, __last). 68 69 auto __trail = __first; 70 auto __lead = __ret; 71 while (__trail != __ret) { 72 if (__lead == __last) { 73 _VSTD::move(__first, __trail, __ret); 74 return __ret; 75 } 76 ++__trail; 77 ++__lead; 78 } 79 80 _ForwardIterator __mid = __first; 81 while (true) { 82 if (__lead == __last) { 83 __trail = _VSTD::move(__mid, __ret, __trail); 84 _VSTD::move(__first, __mid, __trail); 85 return __ret; 86 } 87 swap(*__mid, *__trail); 88 ++__mid; 89 ++__trail; 90 ++__lead; 91 if (__mid == __ret) { 92 __mid = __first; 93 } 94 } 95 } 96 } 97 98 #endif // _LIBCPP_STD_VER > 17 99 100 _LIBCPP_END_NAMESPACE_STD 101 102 #endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H 103