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 <__concepts/assignable.h> 15 #include <__concepts/same_as.h> 16 #include <__config> 17 #include <__iterator/concepts.h> 18 #include <__iterator/incrementable_traits.h> 19 #include <__iterator/iterator_traits.h> 20 #include <__type_traits/enable_if.h> 21 #include <__type_traits/is_integral.h> 22 #include <__utility/convert_to_integral.h> 23 #include <__utility/declval.h> 24 #include <__utility/move.h> 25 #include <__utility/unreachable.h> 26 #include <limits> 27 28 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 29 # pragma GCC system_header 30 #endif 31 32 _LIBCPP_PUSH_MACROS 33 #include <__undef_macros> 34 35 _LIBCPP_BEGIN_NAMESPACE_STD 36 37 template <class _InputIter> 38 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 39 void __advance(_InputIter& __i, typename iterator_traits<_InputIter>::difference_type __n, input_iterator_tag) { 40 for (; __n > 0; --__n) 41 ++__i; 42 } 43 44 template <class _BiDirIter> 45 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 46 void __advance(_BiDirIter& __i, typename iterator_traits<_BiDirIter>::difference_type __n, bidirectional_iterator_tag) { 47 if (__n >= 0) 48 for (; __n > 0; --__n) 49 ++__i; 50 else 51 for (; __n < 0; ++__n) 52 --__i; 53 } 54 55 template <class _RandIter> 56 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 57 void __advance(_RandIter& __i, typename iterator_traits<_RandIter>::difference_type __n, random_access_iterator_tag) { 58 __i += __n; 59 } 60 61 template < 62 class _InputIter, class _Distance, 63 class _IntegralDistance = decltype(_VSTD::__convert_to_integral(std::declval<_Distance>())), 64 class = __enable_if_t<is_integral<_IntegralDistance>::value> > 65 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 66 void advance(_InputIter& __i, _Distance __orig_n) { 67 typedef typename iterator_traits<_InputIter>::difference_type _Difference; 68 _Difference __n = static_cast<_Difference>(_VSTD::__convert_to_integral(__orig_n)); 69 _LIBCPP_ASSERT_UNCATEGORIZED(__n >= 0 || __has_bidirectional_iterator_category<_InputIter>::value, 70 "Attempt to advance(it, n) with negative n on a non-bidirectional iterator"); 71 _VSTD::__advance(__i, __n, typename iterator_traits<_InputIter>::iterator_category()); 72 } 73 74 #if _LIBCPP_STD_VER >= 20 75 76 // [range.iter.op.advance] 77 78 namespace ranges { 79 namespace __advance { 80 81 struct __fn { 82 private: 83 template <class _Ip> 84 _LIBCPP_HIDE_FROM_ABI 85 static constexpr void __advance_forward(_Ip& __i, iter_difference_t<_Ip> __n) { 86 while (__n > 0) { 87 --__n; 88 ++__i; 89 } 90 } 91 92 template <class _Ip> 93 _LIBCPP_HIDE_FROM_ABI 94 static constexpr void __advance_backward(_Ip& __i, iter_difference_t<_Ip> __n) { 95 while (__n < 0) { 96 ++__n; 97 --__i; 98 } 99 } 100 101 public: 102 // Preconditions: If `I` does not model `bidirectional_iterator`, `n` is not negative. 103 template <input_or_output_iterator _Ip> 104 _LIBCPP_HIDE_FROM_ABI 105 constexpr void operator()(_Ip& __i, iter_difference_t<_Ip> __n) const { 106 _LIBCPP_ASSERT_UNCATEGORIZED(__n >= 0 || bidirectional_iterator<_Ip>, 107 "If `n < 0`, then `bidirectional_iterator<I>` must be true."); 108 109 // If `I` models `random_access_iterator`, equivalent to `i += n`. 110 if constexpr (random_access_iterator<_Ip>) { 111 __i += __n; 112 return; 113 } else if constexpr (bidirectional_iterator<_Ip>) { 114 // Otherwise, if `n` is non-negative, increments `i` by `n`. 115 __advance_forward(__i, __n); 116 // Otherwise, decrements `i` by `-n`. 117 __advance_backward(__i, __n); 118 return; 119 } else { 120 // Otherwise, if `n` is non-negative, increments `i` by `n`. 121 __advance_forward(__i, __n); 122 return; 123 } 124 } 125 126 // Preconditions: Either `assignable_from<I&, S> || sized_sentinel_for<S, I>` is modeled, or [i, bound_sentinel) denotes a range. 127 template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp> 128 _LIBCPP_HIDE_FROM_ABI constexpr void operator()(_Ip& __i, _Sp __bound_sentinel) const { 129 // If `I` and `S` model `assignable_from<I&, S>`, equivalent to `i = std::move(bound_sentinel)`. 130 if constexpr (assignable_from<_Ip&, _Sp>) { 131 __i = _VSTD::move(__bound_sentinel); 132 } 133 // Otherwise, if `S` and `I` model `sized_sentinel_for<S, I>`, equivalent to `ranges::advance(i, bound_sentinel - i)`. 134 else if constexpr (sized_sentinel_for<_Sp, _Ip>) { 135 (*this)(__i, __bound_sentinel - __i); 136 } 137 // Otherwise, while `bool(i != bound_sentinel)` is true, increments `i`. 138 else { 139 while (__i != __bound_sentinel) { 140 ++__i; 141 } 142 } 143 } 144 145 // Preconditions: 146 // * If `n > 0`, [i, bound_sentinel) denotes a range. 147 // * If `n == 0`, [i, bound_sentinel) or [bound_sentinel, i) denotes a range. 148 // * If `n < 0`, [bound_sentinel, i) denotes a range, `I` models `bidirectional_iterator`, and `I` and `S` model `same_as<I, S>`. 149 // Returns: `n - M`, where `M` is the difference between the ending and starting position. 150 template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp> 151 _LIBCPP_HIDE_FROM_ABI constexpr iter_difference_t<_Ip> operator()(_Ip& __i, iter_difference_t<_Ip> __n, 152 _Sp __bound_sentinel) const { 153 _LIBCPP_ASSERT_UNCATEGORIZED((__n >= 0) || (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>), 154 "If `n < 0`, then `bidirectional_iterator<I> && same_as<I, S>` must be true."); 155 // If `S` and `I` model `sized_sentinel_for<S, I>`: 156 if constexpr (sized_sentinel_for<_Sp, _Ip>) { 157 // If |n| >= |bound_sentinel - i|, equivalent to `ranges::advance(i, bound_sentinel)`. 158 // __magnitude_geq(a, b) returns |a| >= |b|, assuming they have the same sign. 159 auto __magnitude_geq = [](auto __a, auto __b) { 160 return __a == 0 ? __b == 0 : 161 __a > 0 ? __a >= __b : 162 __a <= __b; 163 }; 164 if (const auto __m = __bound_sentinel - __i; __magnitude_geq(__n, __m)) { 165 (*this)(__i, __bound_sentinel); 166 return __n - __m; 167 } 168 169 // Otherwise, equivalent to `ranges::advance(i, n)`. 170 (*this)(__i, __n); 171 return 0; 172 } else { 173 // Otherwise, if `n` is non-negative, while `bool(i != bound_sentinel)` is true, increments `i` but at 174 // most `n` times. 175 while (__i != __bound_sentinel && __n > 0) { 176 ++__i; 177 --__n; 178 } 179 180 // Otherwise, while `bool(i != bound_sentinel)` is true, decrements `i` but at most `-n` times. 181 if constexpr (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>) { 182 while (__i != __bound_sentinel && __n < 0) { 183 --__i; 184 ++__n; 185 } 186 } 187 return __n; 188 } 189 190 __libcpp_unreachable(); 191 } 192 }; 193 194 } // namespace __advance 195 196 inline namespace __cpo { 197 inline constexpr auto advance = __advance::__fn{}; 198 } // namespace __cpo 199 } // namespace ranges 200 201 #endif // _LIBCPP_STD_VER >= 20 202 203 _LIBCPP_END_NAMESPACE_STD 204 205 _LIBCPP_POP_MACROS 206 207 #endif // _LIBCPP___ITERATOR_ADVANCE_H 208