1 // Functions used by iterators -*- C++ -*-
2
3 // Copyright (C) 2001-2022 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24
25 /*
26 *
27 * Copyright (c) 1994
28 * Hewlett-Packard Company
29 *
30 * Permission to use, copy, modify, distribute and sell this software
31 * and its documentation for any purpose is hereby granted without fee,
32 * provided that the above copyright notice appear in all copies and
33 * that both that copyright notice and this permission notice appear
34 * in supporting documentation. Hewlett-Packard Company makes no
35 * representations about the suitability of this software for any
36 * purpose. It is provided "as is" without express or implied warranty.
37 *
38 *
39 * Copyright (c) 1996-1998
40 * Silicon Graphics Computer Systems, Inc.
41 *
42 * Permission to use, copy, modify, distribute and sell this software
43 * and its documentation for any purpose is hereby granted without fee,
44 * provided that the above copyright notice appear in all copies and
45 * that both that copyright notice and this permission notice appear
46 * in supporting documentation. Silicon Graphics makes no
47 * representations about the suitability of this software for any
48 * purpose. It is provided "as is" without express or implied warranty.
49 */
50
51 /** @file bits/stl_iterator_base_funcs.h
52 * This is an internal header file, included by other library headers.
53 * Do not attempt to use it directly. @headername{iterator}
54 *
55 * This file contains all of the general iterator-related utility
56 * functions, such as distance() and advance().
57 */
58
59 #ifndef _STL_ITERATOR_BASE_FUNCS_H
60 #define _STL_ITERATOR_BASE_FUNCS_H 1
61
62 #pragma GCC system_header
63
64 #include <bits/concept_check.h>
65 #include <debug/assertions.h>
66 #include <bits/stl_iterator_base_types.h>
67
_GLIBCXX_VISIBILITY(default)68 namespace std _GLIBCXX_VISIBILITY(default)
69 {
70 _GLIBCXX_BEGIN_NAMESPACE_VERSION
71
72 _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
73 // Forward declaration for the overloads of __distance.
74 template <typename> struct _List_iterator;
75 template <typename> struct _List_const_iterator;
76 _GLIBCXX_END_NAMESPACE_CONTAINER
77
78 template<typename _InputIterator>
79 inline _GLIBCXX14_CONSTEXPR
80 typename iterator_traits<_InputIterator>::difference_type
81 __distance(_InputIterator __first, _InputIterator __last,
82 input_iterator_tag)
83 {
84 // concept requirements
85 __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
86
87 typename iterator_traits<_InputIterator>::difference_type __n = 0;
88 while (__first != __last)
89 {
90 ++__first;
91 ++__n;
92 }
93 return __n;
94 }
95
96 template<typename _RandomAccessIterator>
97 inline _GLIBCXX14_CONSTEXPR
98 typename iterator_traits<_RandomAccessIterator>::difference_type
99 __distance(_RandomAccessIterator __first, _RandomAccessIterator __last,
100 random_access_iterator_tag)
101 {
102 // concept requirements
103 __glibcxx_function_requires(_RandomAccessIteratorConcept<
104 _RandomAccessIterator>)
105 return __last - __first;
106 }
107
108 #if _GLIBCXX_USE_CXX11_ABI
109 // Forward declaration because of the qualified call in distance.
110 template<typename _Tp>
111 ptrdiff_t
112 __distance(_GLIBCXX_STD_C::_List_iterator<_Tp>,
113 _GLIBCXX_STD_C::_List_iterator<_Tp>,
114 input_iterator_tag);
115
116 template<typename _Tp>
117 ptrdiff_t
118 __distance(_GLIBCXX_STD_C::_List_const_iterator<_Tp>,
119 _GLIBCXX_STD_C::_List_const_iterator<_Tp>,
120 input_iterator_tag);
121 #endif
122
123 #if __cplusplus >= 201103L
124 // Give better error if std::distance called with a non-Cpp17InputIterator.
125 template<typename _OutputIterator>
126 void
127 __distance(_OutputIterator, _OutputIterator, output_iterator_tag) = delete;
128 #endif
129
130 /**
131 * @brief A generalization of pointer arithmetic.
132 * @param __first An input iterator.
133 * @param __last An input iterator.
134 * @return The distance between them.
135 *
136 * Returns @c n such that __first + n == __last. This requires
137 * that @p __last must be reachable from @p __first. Note that @c
138 * n may be negative.
139 *
140 * For random access iterators, this uses their @c + and @c - operations
141 * and are constant time. For other %iterator classes they are linear time.
142 */
143 template<typename _InputIterator>
144 _GLIBCXX_NODISCARD
145 inline _GLIBCXX17_CONSTEXPR
146 typename iterator_traits<_InputIterator>::difference_type
147 distance(_InputIterator __first, _InputIterator __last)
148 {
149 // concept requirements -- taken care of in __distance
150 return std::__distance(__first, __last,
151 std::__iterator_category(__first));
152 }
153
154 template<typename _InputIterator, typename _Distance>
155 inline _GLIBCXX14_CONSTEXPR void
156 __advance(_InputIterator& __i, _Distance __n, input_iterator_tag)
157 {
158 // concept requirements
159 __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
160 __glibcxx_assert(__n >= 0);
161 while (__n--)
162 ++__i;
163 }
164
165 template<typename _BidirectionalIterator, typename _Distance>
166 inline _GLIBCXX14_CONSTEXPR void
167 __advance(_BidirectionalIterator& __i, _Distance __n,
168 bidirectional_iterator_tag)
169 {
170 // concept requirements
171 __glibcxx_function_requires(_BidirectionalIteratorConcept<
172 _BidirectionalIterator>)
173 if (__n > 0)
174 while (__n--)
175 ++__i;
176 else
177 while (__n++)
178 --__i;
179 }
180
181 template<typename _RandomAccessIterator, typename _Distance>
182 inline _GLIBCXX14_CONSTEXPR void
183 __advance(_RandomAccessIterator& __i, _Distance __n,
184 random_access_iterator_tag)
185 {
186 // concept requirements
187 __glibcxx_function_requires(_RandomAccessIteratorConcept<
188 _RandomAccessIterator>)
189 if (__builtin_constant_p(__n) && __n == 1)
190 ++__i;
191 else if (__builtin_constant_p(__n) && __n == -1)
192 --__i;
193 else
194 __i += __n;
195 }
196
197 #if __cplusplus >= 201103L
198 // Give better error if std::advance called with a non-Cpp17InputIterator.
199 template<typename _OutputIterator, typename _Distance>
200 void
201 __advance(_OutputIterator&, _Distance, output_iterator_tag) = delete;
202 #endif
203
204 /**
205 * @brief A generalization of pointer arithmetic.
206 * @param __i An input iterator.
207 * @param __n The @a delta by which to change @p __i.
208 * @return Nothing.
209 *
210 * This increments @p i by @p n. For bidirectional and random access
211 * iterators, @p __n may be negative, in which case @p __i is decremented.
212 *
213 * For random access iterators, this uses their @c + and @c - operations
214 * and are constant time. For other %iterator classes they are linear time.
215 */
216 template<typename _InputIterator, typename _Distance>
217 inline _GLIBCXX17_CONSTEXPR void
218 advance(_InputIterator& __i, _Distance __n)
219 {
220 // concept requirements -- taken care of in __advance
221 typename iterator_traits<_InputIterator>::difference_type __d = __n;
222 std::__advance(__i, __d, std::__iterator_category(__i));
223 }
224
225 #if __cplusplus >= 201103L
226
227 template<typename _InputIterator>
228 _GLIBCXX_NODISCARD
229 inline _GLIBCXX17_CONSTEXPR _InputIterator
230 next(_InputIterator __x, typename
231 iterator_traits<_InputIterator>::difference_type __n = 1)
232 {
233 // concept requirements
234 __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
235 std::advance(__x, __n);
236 return __x;
237 }
238
239 template<typename _BidirectionalIterator>
240 _GLIBCXX_NODISCARD
241 inline _GLIBCXX17_CONSTEXPR _BidirectionalIterator
242 prev(_BidirectionalIterator __x, typename
243 iterator_traits<_BidirectionalIterator>::difference_type __n = 1)
244 {
245 // concept requirements
246 __glibcxx_function_requires(_BidirectionalIteratorConcept<
247 _BidirectionalIterator>)
248 std::advance(__x, -__n);
249 return __x;
250 }
251
252 #endif // C++11
253
254 _GLIBCXX_END_NAMESPACE_VERSION
255 } // namespace
256
257 #endif /* _STL_ITERATOR_BASE_FUNCS_H */
258