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1 //===----------------------------------------------------------------------===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8
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9 #ifndef _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
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10 #define _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
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11
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12 #include <__config>
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13 #include <__algorithm/move.h>
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14 #include <__algorithm/move_backward.h>
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15 #include <__algorithm/swap_ranges.h>
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16 #include <__iterator/iterator_traits.h>
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17 #include <type_traits> // swap
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18
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19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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20 #pragma GCC system_header
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21 #endif
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22
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23 _LIBCPP_PUSH_MACROS
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24 #include <__undef_macros>
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25
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26 _LIBCPP_BEGIN_NAMESPACE_STD
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27
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28 #if _LIBCPP_STD_VER > 17
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29
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30 template <class _ForwardIterator>
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31 inline _LIBCPP_INLINE_VISIBILITY constexpr
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32 _ForwardIterator
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33 shift_right(_ForwardIterator __first, _ForwardIterator __last,
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34 typename iterator_traits<_ForwardIterator>::difference_type __n)
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35 {
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36 if (__n == 0) {
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37 return __first;
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38 }
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39
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40 if constexpr (__is_cpp17_random_access_iterator<_ForwardIterator>::value) {
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41 decltype(__n) __d = __last - __first;
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42 if (__n >= __d) {
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43 return __last;
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44 }
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45 _ForwardIterator __m = __first + (__d - __n);
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46 return _VSTD::move_backward(__first, __m, __last);
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47 } else if constexpr (__is_cpp17_bidirectional_iterator<_ForwardIterator>::value) {
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48 _ForwardIterator __m = __last;
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49 for (; __n > 0; --__n) {
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50 if (__m == __first) {
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51 return __last;
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52 }
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53 --__m;
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54 }
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55 return _VSTD::move_backward(__first, __m, __last);
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56 } else {
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57 _ForwardIterator __ret = __first;
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58 for (; __n > 0; --__n) {
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59 if (__ret == __last) {
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60 return __last;
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61 }
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62 ++__ret;
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63 }
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64
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65 // We have an __n-element scratch space from __first to __ret.
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66 // Slide an __n-element window [__trail, __lead) from left to right.
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67 // We're essentially doing swap_ranges(__first, __ret, __trail, __lead)
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68 // over and over; but once __lead reaches __last we needn't bother
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69 // to save the values of elements [__trail, __last).
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70
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71 auto __trail = __first;
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72 auto __lead = __ret;
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73 while (__trail != __ret) {
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74 if (__lead == __last) {
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75 _VSTD::move(__first, __trail, __ret);
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76 return __ret;
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77 }
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78 ++__trail;
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79 ++__lead;
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80 }
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81
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82 _ForwardIterator __mid = __first;
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83 while (true) {
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84 if (__lead == __last) {
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85 __trail = _VSTD::move(__mid, __ret, __trail);
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86 _VSTD::move(__first, __mid, __trail);
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87 return __ret;
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88 }
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89 swap(*__mid, *__trail);
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90 ++__mid;
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91 ++__trail;
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92 ++__lead;
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93 if (__mid == __ret) {
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94 __mid = __first;
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95 }
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96 }
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97 }
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98 }
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99
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100 #endif // _LIBCPP_STD_VER > 17
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101
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102 _LIBCPP_END_NAMESPACE_STD
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103
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104 _LIBCPP_POP_MACROS
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105
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106 #endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
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