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
__advance(_InputIter & __i,typename iterator_traits<_InputIter>::difference_type __n,input_iterator_tag)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
__advance(_BiDirIter & __i,typename iterator_traits<_BiDirIter>::difference_type __n,bidirectional_iterator_tag)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
__advance(_RandIter & __i,typename iterator_traits<_RandIter>::difference_type __n,random_access_iterator_tag)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
advance(_InputIter & __i,_Distance __orig_n)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
__advance_forward__fn79 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
__advance_backward__fn88 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
operator__fn99 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>
operator__fn122 _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>
operator__fn145 _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