1 // Functions used by iterators -*- C++ -*-
2
3 // Copyright (C) 2001-2023 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
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 __attribute__((__always_inline__))
98 inline _GLIBCXX14_CONSTEXPR
99 typename iterator_traits<_RandomAccessIterator>::difference_type
100 __distance(_RandomAccessIterator __first, _RandomAccessIterator __last,
101 random_access_iterator_tag)
102 {
103 // concept requirements
104 __glibcxx_function_requires(_RandomAccessIteratorConcept<
105 _RandomAccessIterator>)
106 return __last - __first;
107 }
108
109 #if _GLIBCXX_USE_CXX11_ABI
110 // Forward declaration because of the qualified call in distance.
111 template<typename _Tp>
112 ptrdiff_t
113 __distance(_GLIBCXX_STD_C::_List_iterator<_Tp>,
114 _GLIBCXX_STD_C::_List_iterator<_Tp>,
115 input_iterator_tag);
116
117 template<typename _Tp>
118 ptrdiff_t
119 __distance(_GLIBCXX_STD_C::_List_const_iterator<_Tp>,
120 _GLIBCXX_STD_C::_List_const_iterator<_Tp>,
121 input_iterator_tag);
122 #endif
123
124 #if __cplusplus >= 201103L
125 // Give better error if std::distance called with a non-Cpp17InputIterator.
126 template<typename _OutputIterator>
127 void
128 __distance(_OutputIterator, _OutputIterator, output_iterator_tag) = delete;
129 #endif
130
131 /**
132 * @brief A generalization of pointer arithmetic.
133 * @param __first An input iterator.
134 * @param __last An input iterator.
135 * @return The distance between them.
136 *
137 * Returns @c n such that __first + n == __last. This requires
138 * that @p __last must be reachable from @p __first. Note that @c
139 * n may be negative.
140 *
141 * For random access iterators, this uses their @c + and @c - operations
142 * and are constant time. For other %iterator classes they are linear time.
143 */
144 template<typename _InputIterator>
145 _GLIBCXX_NODISCARD __attribute__((__always_inline__))
146 inline _GLIBCXX17_CONSTEXPR
147 typename iterator_traits<_InputIterator>::difference_type
148 distance(_InputIterator __first, _InputIterator __last)
149 {
150 // concept requirements -- taken care of in __distance
151 return std::__distance(__first, __last,
152 std::__iterator_category(__first));
153 }
154
155 template<typename _InputIterator, typename _Distance>
156 inline _GLIBCXX14_CONSTEXPR void
157 __advance(_InputIterator& __i, _Distance __n, input_iterator_tag)
158 {
159 // concept requirements
160 __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
161 __glibcxx_assert(__n >= 0);
162 while (__n--)
163 ++__i;
164 }
165
166 template<typename _BidirectionalIterator, typename _Distance>
167 inline _GLIBCXX14_CONSTEXPR void
168 __advance(_BidirectionalIterator& __i, _Distance __n,
169 bidirectional_iterator_tag)
170 {
171 // concept requirements
172 __glibcxx_function_requires(_BidirectionalIteratorConcept<
173 _BidirectionalIterator>)
174 if (__n > 0)
175 while (__n--)
176 ++__i;
177 else
178 while (__n++)
179 --__i;
180 }
181
182 template<typename _RandomAccessIterator, typename _Distance>
183 inline _GLIBCXX14_CONSTEXPR void
184 __advance(_RandomAccessIterator& __i, _Distance __n,
185 random_access_iterator_tag)
186 {
187 // concept requirements
188 __glibcxx_function_requires(_RandomAccessIteratorConcept<
189 _RandomAccessIterator>)
190 if (__builtin_constant_p(__n) && __n == 1)
191 ++__i;
192 else if (__builtin_constant_p(__n) && __n == -1)
193 --__i;
194 else
195 __i += __n;
196 }
197
198 #if __cplusplus >= 201103L
199 // Give better error if std::advance called with a non-Cpp17InputIterator.
200 template<typename _OutputIterator, typename _Distance>
201 void
202 __advance(_OutputIterator&, _Distance, output_iterator_tag) = delete;
203 #endif
204
205 /**
206 * @brief A generalization of pointer arithmetic.
207 * @param __i An input iterator.
208 * @param __n The @a delta by which to change @p __i.
209 * @return Nothing.
210 *
211 * This increments @p i by @p n. For bidirectional and random access
212 * iterators, @p __n may be negative, in which case @p __i is decremented.
213 *
214 * For random access iterators, this uses their @c + and @c - operations
215 * and are constant time. For other %iterator classes they are linear time.
216 */
217 template<typename _InputIterator, typename _Distance>
218 __attribute__((__always_inline__))
219 inline _GLIBCXX17_CONSTEXPR void
220 advance(_InputIterator& __i, _Distance __n)
221 {
222 // concept requirements -- taken care of in __advance
223 typename iterator_traits<_InputIterator>::difference_type __d = __n;
224 std::__advance(__i, __d, std::__iterator_category(__i));
225 }
226
227 #if __cplusplus >= 201103L
228
229 template<typename _InputIterator>
230 _GLIBCXX_NODISCARD [[__gnu__::__always_inline__]]
231 inline _GLIBCXX17_CONSTEXPR _InputIterator
232 next(_InputIterator __x, typename
233 iterator_traits<_InputIterator>::difference_type __n = 1)
234 {
235 // concept requirements
236 __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
237 std::advance(__x, __n);
238 return __x;
239 }
240
241 template<typename _BidirectionalIterator>
242 _GLIBCXX_NODISCARD [[__gnu__::__always_inline__]]
243 inline _GLIBCXX17_CONSTEXPR _BidirectionalIterator
244 prev(_BidirectionalIterator __x, typename
245 iterator_traits<_BidirectionalIterator>::difference_type __n = 1)
246 {
247 // concept requirements
248 __glibcxx_function_requires(_BidirectionalIteratorConcept<
249 _BidirectionalIterator>)
250 std::advance(__x, -__n);
251 return __x;
252 }
253
254 #endif // C++11
255
256 _GLIBCXX_END_NAMESPACE_VERSION
257 } // namespace
258
259 #endif /* _STL_ITERATOR_BASE_FUNCS_H */