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 <__config> 14 #include <__debug> 15 #include <__iterator/concepts.h> 16 #include <__iterator/incrementable_traits.h> 17 #include <__iterator/iterator_traits.h> 18 #include <__utility/move.h> 19 #include <concepts> 20 #include <cstdlib> 21 #include <limits> 22 #include <type_traits> 23 24 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 25 #pragma GCC system_header 26 #endif 27 28 _LIBCPP_BEGIN_NAMESPACE_STD 29 30 template <class _InputIter> 31 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14 32 void __advance(_InputIter& __i, typename iterator_traits<_InputIter>::difference_type __n, input_iterator_tag) { 33 for (; __n > 0; --__n) 34 ++__i; 35 } 36 37 template <class _BiDirIter> 38 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14 39 void __advance(_BiDirIter& __i, typename iterator_traits<_BiDirIter>::difference_type __n, bidirectional_iterator_tag) { 40 if (__n >= 0) 41 for (; __n > 0; --__n) 42 ++__i; 43 else 44 for (; __n < 0; ++__n) 45 --__i; 46 } 47 48 template <class _RandIter> 49 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14 50 void __advance(_RandIter& __i, typename iterator_traits<_RandIter>::difference_type __n, random_access_iterator_tag) { 51 __i += __n; 52 } 53 54 template < 55 class _InputIter, class _Distance, 56 class _IntegralDistance = decltype(_VSTD::__convert_to_integral(declval<_Distance>())), 57 class = __enable_if_t<is_integral<_IntegralDistance>::value> > 58 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14 59 void advance(_InputIter& __i, _Distance __orig_n) { 60 typedef typename iterator_traits<_InputIter>::difference_type _Difference; 61 _Difference __n = static_cast<_Difference>(_VSTD::__convert_to_integral(__orig_n)); 62 _LIBCPP_ASSERT(__n >= 0 || __is_cpp17_bidirectional_iterator<_InputIter>::value, 63 "Attempt to advance(it, n) with negative n on a non-bidirectional iterator"); 64 _VSTD::__advance(__i, __n, typename iterator_traits<_InputIter>::iterator_category()); 65 } 66 67 #if !defined(_LIBCPP_HAS_NO_CONCEPTS) && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES) 68 69 // [range.iter.op.advance] 70 71 namespace ranges { 72 namespace __advance { 73 74 struct __fn { 75 private: 76 template <class _Ip> 77 _LIBCPP_HIDE_FROM_ABI 78 static constexpr void __advance_forward(_Ip& __i, iter_difference_t<_Ip> __n) { 79 while (__n > 0) { 80 --__n; 81 ++__i; 82 } 83 } 84 85 template <class _Ip> 86 _LIBCPP_HIDE_FROM_ABI 87 static constexpr void __advance_backward(_Ip& __i, iter_difference_t<_Ip> __n) { 88 while (__n < 0) { 89 ++__n; 90 --__i; 91 } 92 } 93 94 public: 95 // Preconditions: If `I` does not model `bidirectional_iterator`, `n` is not negative. 96 template <input_or_output_iterator _Ip> 97 _LIBCPP_HIDE_FROM_ABI 98 constexpr void operator()(_Ip& __i, iter_difference_t<_Ip> __n) const { 99 _LIBCPP_ASSERT(__n >= 0 || bidirectional_iterator<_Ip>, 100 "If `n < 0`, then `bidirectional_iterator<I>` must be true."); 101 102 // If `I` models `random_access_iterator`, equivalent to `i += n`. 103 if constexpr (random_access_iterator<_Ip>) { 104 __i += __n; 105 return; 106 } else if constexpr (bidirectional_iterator<_Ip>) { 107 // Otherwise, if `n` is non-negative, increments `i` by `n`. 108 __advance_forward(__i, __n); 109 // Otherwise, decrements `i` by `-n`. 110 __advance_backward(__i, __n); 111 return; 112 } else { 113 // Otherwise, if `n` is non-negative, increments `i` by `n`. 114 __advance_forward(__i, __n); 115 return; 116 } 117 } 118 119 // Preconditions: Either `assignable_from<I&, S> || sized_sentinel_for<S, I>` is modeled, or [i, bound) denotes a range. 120 template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp> 121 _LIBCPP_HIDE_FROM_ABI 122 constexpr void operator()(_Ip& __i, _Sp __bound) const { 123 // If `I` and `S` model `assignable_from<I&, S>`, equivalent to `i = std::move(bound)`. 124 if constexpr (assignable_from<_Ip&, _Sp>) { 125 __i = _VSTD::move(__bound); 126 } 127 // Otherwise, if `S` and `I` model `sized_sentinel_for<S, I>`, equivalent to `ranges::advance(i, bound - i)`. 128 else if constexpr (sized_sentinel_for<_Sp, _Ip>) { 129 (*this)(__i, __bound - __i); 130 } 131 // Otherwise, while `bool(i != bound)` is true, increments `i`. 132 else { 133 while (__i != __bound) { 134 ++__i; 135 } 136 } 137 } 138 139 // Preconditions: 140 // * If `n > 0`, [i, bound) denotes a range. 141 // * If `n == 0`, [i, bound) or [bound, i) denotes a range. 142 // * If `n < 0`, [bound, 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 the ending and starting position. 144 template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp> 145 _LIBCPP_HIDE_FROM_ABI 146 constexpr iter_difference_t<_Ip> operator()(_Ip& __i, iter_difference_t<_Ip> __n, _Sp __bound) 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 - i|, equivalent to `ranges::advance(i, bound)`. 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 - __i; __magnitude_geq(__n, __M)) { 159 (*this)(__i, __bound); 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)` is true, increments `i` but at 168 // most `n` times. 169 while (__i != __bound && __n > 0) { 170 ++__i; 171 --__n; 172 } 173 174 // Otherwise, while `bool(i != bound)` is true, decrements `i` but at most `-n` times. 175 if constexpr (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>) { 176 while (__i != __bound && __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 // !defined(_LIBCPP_HAS_NO_CONCEPTS) && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES) 196 197 _LIBCPP_END_NAMESPACE_STD 198 199 #endif // _LIBCPP___ITERATOR_ADVANCE_H 200