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 <cstdlib> 27 #include <limits> 28 29 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 30 # pragma GCC system_header 31 #endif 32 33 _LIBCPP_BEGIN_NAMESPACE_STD 34 35 template <class _InputIter> 36 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 37 void __advance(_InputIter& __i, typename iterator_traits<_InputIter>::difference_type __n, input_iterator_tag) { 38 for (; __n > 0; --__n) 39 ++__i; 40 } 41 42 template <class _BiDirIter> 43 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 44 void __advance(_BiDirIter& __i, typename iterator_traits<_BiDirIter>::difference_type __n, bidirectional_iterator_tag) { 45 if (__n >= 0) 46 for (; __n > 0; --__n) 47 ++__i; 48 else 49 for (; __n < 0; ++__n) 50 --__i; 51 } 52 53 template <class _RandIter> 54 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 55 void __advance(_RandIter& __i, typename iterator_traits<_RandIter>::difference_type __n, random_access_iterator_tag) { 56 __i += __n; 57 } 58 59 template < 60 class _InputIter, class _Distance, 61 class _IntegralDistance = decltype(_VSTD::__convert_to_integral(std::declval<_Distance>())), 62 class = __enable_if_t<is_integral<_IntegralDistance>::value> > 63 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 64 void advance(_InputIter& __i, _Distance __orig_n) { 65 typedef typename iterator_traits<_InputIter>::difference_type _Difference; 66 _Difference __n = static_cast<_Difference>(_VSTD::__convert_to_integral(__orig_n)); 67 _LIBCPP_ASSERT(__n >= 0 || __is_cpp17_bidirectional_iterator<_InputIter>::value, 68 "Attempt to advance(it, n) with negative n on a non-bidirectional iterator"); 69 _VSTD::__advance(__i, __n, typename iterator_traits<_InputIter>::iterator_category()); 70 } 71 72 #if _LIBCPP_STD_VER > 17 73 74 // [range.iter.op.advance] 75 76 namespace ranges { 77 namespace __advance { 78 79 struct __fn { 80 private: 81 template <class _Ip> 82 _LIBCPP_HIDE_FROM_ABI 83 static constexpr void __advance_forward(_Ip& __i, iter_difference_t<_Ip> __n) { 84 while (__n > 0) { 85 --__n; 86 ++__i; 87 } 88 } 89 90 template <class _Ip> 91 _LIBCPP_HIDE_FROM_ABI 92 static constexpr void __advance_backward(_Ip& __i, iter_difference_t<_Ip> __n) { 93 while (__n < 0) { 94 ++__n; 95 --__i; 96 } 97 } 98 99 public: 100 // Preconditions: If `I` does not model `bidirectional_iterator`, `n` is not negative. 101 template <input_or_output_iterator _Ip> 102 _LIBCPP_HIDE_FROM_ABI 103 constexpr void operator()(_Ip& __i, iter_difference_t<_Ip> __n) const { 104 _LIBCPP_ASSERT(__n >= 0 || bidirectional_iterator<_Ip>, 105 "If `n < 0`, then `bidirectional_iterator<I>` must be true."); 106 107 // If `I` models `random_access_iterator`, equivalent to `i += n`. 108 if constexpr (random_access_iterator<_Ip>) { 109 __i += __n; 110 return; 111 } else if constexpr (bidirectional_iterator<_Ip>) { 112 // Otherwise, if `n` is non-negative, increments `i` by `n`. 113 __advance_forward(__i, __n); 114 // Otherwise, decrements `i` by `-n`. 115 __advance_backward(__i, __n); 116 return; 117 } else { 118 // Otherwise, if `n` is non-negative, increments `i` by `n`. 119 __advance_forward(__i, __n); 120 return; 121 } 122 } 123 124 // Preconditions: Either `assignable_from<I&, S> || sized_sentinel_for<S, I>` is modeled, or [i, bound_sentinel) denotes a range. 125 template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp> 126 _LIBCPP_HIDE_FROM_ABI constexpr void operator()(_Ip& __i, _Sp __bound_sentinel) const { 127 // If `I` and `S` model `assignable_from<I&, S>`, equivalent to `i = std::move(bound_sentinel)`. 128 if constexpr (assignable_from<_Ip&, _Sp>) { 129 __i = _VSTD::move(__bound_sentinel); 130 } 131 // Otherwise, if `S` and `I` model `sized_sentinel_for<S, I>`, equivalent to `ranges::advance(i, bound_sentinel - i)`. 132 else if constexpr (sized_sentinel_for<_Sp, _Ip>) { 133 (*this)(__i, __bound_sentinel - __i); 134 } 135 // Otherwise, while `bool(i != bound_sentinel)` is true, increments `i`. 136 else { 137 while (__i != __bound_sentinel) { 138 ++__i; 139 } 140 } 141 } 142 143 // Preconditions: 144 // * If `n > 0`, [i, bound_sentinel) denotes a range. 145 // * If `n == 0`, [i, bound_sentinel) or [bound_sentinel, i) denotes a range. 146 // * If `n < 0`, [bound_sentinel, i) denotes a range, `I` models `bidirectional_iterator`, and `I` and `S` model `same_as<I, S>`. 147 // Returns: `n - M`, where `M` is the difference between the ending and starting position. 148 template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp> 149 _LIBCPP_HIDE_FROM_ABI constexpr iter_difference_t<_Ip> operator()(_Ip& __i, iter_difference_t<_Ip> __n, 150 _Sp __bound_sentinel) const { 151 _LIBCPP_ASSERT((__n >= 0) || (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>), 152 "If `n < 0`, then `bidirectional_iterator<I> && same_as<I, S>` must be true."); 153 // If `S` and `I` model `sized_sentinel_for<S, I>`: 154 if constexpr (sized_sentinel_for<_Sp, _Ip>) { 155 // If |n| >= |bound_sentinel - i|, equivalent to `ranges::advance(i, bound_sentinel)`. 156 // __magnitude_geq(a, b) returns |a| >= |b|, assuming they have the same sign. 157 auto __magnitude_geq = [](auto __a, auto __b) { 158 return __a == 0 ? __b == 0 : 159 __a > 0 ? __a >= __b : 160 __a <= __b; 161 }; 162 if (const auto __M = __bound_sentinel - __i; __magnitude_geq(__n, __M)) { 163 (*this)(__i, __bound_sentinel); 164 return __n - __M; 165 } 166 167 // Otherwise, equivalent to `ranges::advance(i, n)`. 168 (*this)(__i, __n); 169 return 0; 170 } else { 171 // Otherwise, if `n` is non-negative, while `bool(i != bound_sentinel)` is true, increments `i` but at 172 // most `n` times. 173 while (__i != __bound_sentinel && __n > 0) { 174 ++__i; 175 --__n; 176 } 177 178 // Otherwise, while `bool(i != bound_sentinel)` is true, decrements `i` but at most `-n` times. 179 if constexpr (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>) { 180 while (__i != __bound_sentinel && __n < 0) { 181 --__i; 182 ++__n; 183 } 184 } 185 return __n; 186 } 187 188 __libcpp_unreachable(); 189 } 190 }; 191 192 } // namespace __advance 193 194 inline namespace __cpo { 195 inline constexpr auto advance = __advance::__fn{}; 196 } // namespace __cpo 197 } // namespace ranges 198 199 #endif // _LIBCPP_STD_VER > 17 200 201 _LIBCPP_END_NAMESPACE_STD 202 203 #endif // _LIBCPP___ITERATOR_ADVANCE_H 204