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 <__config> 13 #include <__algorithm/move.h> 14 #include <__algorithm/move_backward.h> 15 #include <__algorithm/swap_ranges.h> 16 #include <__iterator/iterator_traits.h> 17 #include <type_traits> // swap 18 19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 20 #pragma GCC system_header 21 #endif 22 23 _LIBCPP_PUSH_MACROS 24 #include <__undef_macros> 25 26 _LIBCPP_BEGIN_NAMESPACE_STD 27 28 #if _LIBCPP_STD_VER > 17 29 30 template <class _ForwardIterator> 31 inline _LIBCPP_INLINE_VISIBILITY constexpr 32 _ForwardIterator 33 shift_right(_ForwardIterator __first, _ForwardIterator __last, 34 typename iterator_traits<_ForwardIterator>::difference_type __n) 35 { 36 if (__n == 0) { 37 return __first; 38 } 39 40 if constexpr (__is_cpp17_random_access_iterator<_ForwardIterator>::value) { 41 decltype(__n) __d = __last - __first; 42 if (__n >= __d) { 43 return __last; 44 } 45 _ForwardIterator __m = __first + (__d - __n); 46 return _VSTD::move_backward(__first, __m, __last); 47 } else if constexpr (__is_cpp17_bidirectional_iterator<_ForwardIterator>::value) { 48 _ForwardIterator __m = __last; 49 for (; __n > 0; --__n) { 50 if (__m == __first) { 51 return __last; 52 } 53 --__m; 54 } 55 return _VSTD::move_backward(__first, __m, __last); 56 } else { 57 _ForwardIterator __ret = __first; 58 for (; __n > 0; --__n) { 59 if (__ret == __last) { 60 return __last; 61 } 62 ++__ret; 63 } 64 65 // We have an __n-element scratch space from __first to __ret. 66 // Slide an __n-element window [__trail, __lead) from left to right. 67 // We're essentially doing swap_ranges(__first, __ret, __trail, __lead) 68 // over and over; but once __lead reaches __last we needn't bother 69 // to save the values of elements [__trail, __last). 70 71 auto __trail = __first; 72 auto __lead = __ret; 73 while (__trail != __ret) { 74 if (__lead == __last) { 75 _VSTD::move(__first, __trail, __ret); 76 return __ret; 77 } 78 ++__trail; 79 ++__lead; 80 } 81 82 _ForwardIterator __mid = __first; 83 while (true) { 84 if (__lead == __last) { 85 __trail = _VSTD::move(__mid, __ret, __trail); 86 _VSTD::move(__first, __mid, __trail); 87 return __ret; 88 } 89 swap(*__mid, *__trail); 90 ++__mid; 91 ++__trail; 92 ++__lead; 93 if (__mid == __ret) { 94 __mid = __first; 95 } 96 } 97 } 98 } 99 100 #endif // _LIBCPP_STD_VER > 17 101 102 _LIBCPP_END_NAMESPACE_STD 103 104 _LIBCPP_POP_MACROS 105 106 #endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H 107