1 // -*- C++ -*- 2 //===----------------------------------------------------------------------===// 3 // 4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 5 // See https://llvm.org/LICENSE.txt for license information. 6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 7 // 8 //===----------------------------------------------------------------------===// 9 10 #ifndef _LIBCPP___ITERATOR_ADVANCE_H 11 #define _LIBCPP___ITERATOR_ADVANCE_H 12 13 #include <__assert> 14 #include <__config> 15 #include <__iterator/concepts.h> 16 #include <__iterator/incrementable_traits.h> 17 #include <__iterator/iterator_traits.h> 18 #include <__utility/move.h> 19 #include <__utility/unreachable.h> 20 #include <concepts> 21 #include <cstdlib> 22 #include <limits> 23 #include <type_traits> 24 25 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 26 # pragma GCC system_header 27 #endif 28 29 _LIBCPP_BEGIN_NAMESPACE_STD 30 31 template <class _InputIter> 32 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14 33 void __advance(_InputIter& __i, typename iterator_traits<_InputIter>::difference_type __n, input_iterator_tag) { 34 for (; __n > 0; --__n) 35 ++__i; 36 } 37 38 template <class _BiDirIter> 39 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14 40 void __advance(_BiDirIter& __i, typename iterator_traits<_BiDirIter>::difference_type __n, bidirectional_iterator_tag) { 41 if (__n >= 0) 42 for (; __n > 0; --__n) 43 ++__i; 44 else 45 for (; __n < 0; ++__n) 46 --__i; 47 } 48 49 template <class _RandIter> 50 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14 51 void __advance(_RandIter& __i, typename iterator_traits<_RandIter>::difference_type __n, random_access_iterator_tag) { 52 __i += __n; 53 } 54 55 template < 56 class _InputIter, class _Distance, 57 class _IntegralDistance = decltype(_VSTD::__convert_to_integral(declval<_Distance>())), 58 class = __enable_if_t<is_integral<_IntegralDistance>::value> > 59 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14 60 void advance(_InputIter& __i, _Distance __orig_n) { 61 typedef typename iterator_traits<_InputIter>::difference_type _Difference; 62 _Difference __n = static_cast<_Difference>(_VSTD::__convert_to_integral(__orig_n)); 63 _LIBCPP_ASSERT(__n >= 0 || __is_cpp17_bidirectional_iterator<_InputIter>::value, 64 "Attempt to advance(it, n) with negative n on a non-bidirectional iterator"); 65 _VSTD::__advance(__i, __n, typename iterator_traits<_InputIter>::iterator_category()); 66 } 67 68 #if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES) 69 70 // [range.iter.op.advance] 71 72 namespace ranges { 73 namespace __advance { 74 75 struct __fn { 76 private: 77 template <class _Ip> 78 _LIBCPP_HIDE_FROM_ABI 79 static constexpr void __advance_forward(_Ip& __i, iter_difference_t<_Ip> __n) { 80 while (__n > 0) { 81 --__n; 82 ++__i; 83 } 84 } 85 86 template <class _Ip> 87 _LIBCPP_HIDE_FROM_ABI 88 static constexpr void __advance_backward(_Ip& __i, iter_difference_t<_Ip> __n) { 89 while (__n < 0) { 90 ++__n; 91 --__i; 92 } 93 } 94 95 public: 96 // Preconditions: If `I` does not model `bidirectional_iterator`, `n` is not negative. 97 template <input_or_output_iterator _Ip> 98 _LIBCPP_HIDE_FROM_ABI 99 constexpr void operator()(_Ip& __i, iter_difference_t<_Ip> __n) const { 100 _LIBCPP_ASSERT(__n >= 0 || bidirectional_iterator<_Ip>, 101 "If `n < 0`, then `bidirectional_iterator<I>` must be true."); 102 103 // If `I` models `random_access_iterator`, equivalent to `i += n`. 104 if constexpr (random_access_iterator<_Ip>) { 105 __i += __n; 106 return; 107 } else if constexpr (bidirectional_iterator<_Ip>) { 108 // Otherwise, if `n` is non-negative, increments `i` by `n`. 109 __advance_forward(__i, __n); 110 // Otherwise, decrements `i` by `-n`. 111 __advance_backward(__i, __n); 112 return; 113 } else { 114 // Otherwise, if `n` is non-negative, increments `i` by `n`. 115 __advance_forward(__i, __n); 116 return; 117 } 118 } 119 120 // Preconditions: Either `assignable_from<I&, S> || sized_sentinel_for<S, I>` is modeled, or [i, bound_sentinel) denotes a range. 121 template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp> 122 _LIBCPP_HIDE_FROM_ABI constexpr void operator()(_Ip& __i, _Sp __bound_sentinel) const { 123 // If `I` and `S` model `assignable_from<I&, S>`, equivalent to `i = std::move(bound_sentinel)`. 124 if constexpr (assignable_from<_Ip&, _Sp>) { 125 __i = _VSTD::move(__bound_sentinel); 126 } 127 // Otherwise, if `S` and `I` model `sized_sentinel_for<S, I>`, equivalent to `ranges::advance(i, bound_sentinel - i)`. 128 else if constexpr (sized_sentinel_for<_Sp, _Ip>) { 129 (*this)(__i, __bound_sentinel - __i); 130 } 131 // Otherwise, while `bool(i != bound_sentinel)` is true, increments `i`. 132 else { 133 while (__i != __bound_sentinel) { 134 ++__i; 135 } 136 } 137 } 138 139 // Preconditions: 140 // * If `n > 0`, [i, bound_sentinel) denotes a range. 141 // * If `n == 0`, [i, bound_sentinel) or [bound_sentinel, i) denotes a range. 142 // * If `n < 0`, [bound_sentinel, i) denotes a range, `I` models `bidirectional_iterator`, and `I` and `S` model `same_as<I, S>`. 143 // Returns: `n - M`, where `M` is the difference between the ending and starting position. 144 template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp> 145 _LIBCPP_HIDE_FROM_ABI constexpr iter_difference_t<_Ip> operator()(_Ip& __i, iter_difference_t<_Ip> __n, 146 _Sp __bound_sentinel) const { 147 _LIBCPP_ASSERT((__n >= 0) || (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>), 148 "If `n < 0`, then `bidirectional_iterator<I> && same_as<I, S>` must be true."); 149 // If `S` and `I` model `sized_sentinel_for<S, I>`: 150 if constexpr (sized_sentinel_for<_Sp, _Ip>) { 151 // If |n| >= |bound_sentinel - i|, equivalent to `ranges::advance(i, bound_sentinel)`. 152 // __magnitude_geq(a, b) returns |a| >= |b|, assuming they have the same sign. 153 auto __magnitude_geq = [](auto __a, auto __b) { 154 return __a == 0 ? __b == 0 : 155 __a > 0 ? __a >= __b : 156 __a <= __b; 157 }; 158 if (const auto __M = __bound_sentinel - __i; __magnitude_geq(__n, __M)) { 159 (*this)(__i, __bound_sentinel); 160 return __n - __M; 161 } 162 163 // Otherwise, equivalent to `ranges::advance(i, n)`. 164 (*this)(__i, __n); 165 return 0; 166 } else { 167 // Otherwise, if `n` is non-negative, while `bool(i != bound_sentinel)` is true, increments `i` but at 168 // most `n` times. 169 while (__i != __bound_sentinel && __n > 0) { 170 ++__i; 171 --__n; 172 } 173 174 // Otherwise, while `bool(i != bound_sentinel)` is true, decrements `i` but at most `-n` times. 175 if constexpr (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>) { 176 while (__i != __bound_sentinel && __n < 0) { 177 --__i; 178 ++__n; 179 } 180 } 181 return __n; 182 } 183 184 __libcpp_unreachable(); 185 } 186 }; 187 188 } // namespace __advance 189 190 inline namespace __cpo { 191 inline constexpr auto advance = __advance::__fn{}; 192 } // namespace __cpo 193 } // namespace ranges 194 195 #endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES) 196 197 _LIBCPP_END_NAMESPACE_STD 198 199 #endif // _LIBCPP___ITERATOR_ADVANCE_H 200