1 // Temporary buffer implementation -*- C++ -*-
2
3 // Copyright (C) 2001-2020 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) 1996,1997
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_tempbuf.h
52 * This is an internal header file, included by other library headers.
53 * Do not attempt to use it directly. @headername{memory}
54 */
55
56 #ifndef _STL_TEMPBUF_H
57 #define _STL_TEMPBUF_H 1
58
59 #include <bits/stl_algobase.h>
60 #include <bits/stl_construct.h>
61
_GLIBCXX_VISIBILITY(default)62 namespace std _GLIBCXX_VISIBILITY(default)
63 {
64 _GLIBCXX_BEGIN_NAMESPACE_VERSION
65
66 namespace __detail
67 {
68 template<typename _Tp>
69 inline void
70 __return_temporary_buffer(_Tp* __p,
71 size_t __len __attribute__((__unused__)))
72 {
73 #if __cpp_sized_deallocation
74 ::operator delete(__p, __len * sizeof(_Tp));
75 #else
76 ::operator delete(__p);
77 #endif
78 }
79 }
80
81 /**
82 * @brief Allocates a temporary buffer.
83 * @param __len The number of objects of type Tp.
84 * @return See full description.
85 *
86 * Reinventing the wheel, but this time with prettier spokes!
87 *
88 * This function tries to obtain storage for @c __len adjacent Tp
89 * objects. The objects themselves are not constructed, of course.
90 * A pair<> is returned containing <em>the buffer s address and
91 * capacity (in the units of sizeof(_Tp)), or a pair of 0 values if
92 * no storage can be obtained.</em> Note that the capacity obtained
93 * may be less than that requested if the memory is unavailable;
94 * you should compare len with the .second return value.
95 *
96 * Provides the nothrow exception guarantee.
97 */
98 template<typename _Tp>
99 pair<_Tp*, ptrdiff_t>
100 get_temporary_buffer(ptrdiff_t __len) _GLIBCXX_NOEXCEPT
101 {
102 const ptrdiff_t __max =
103 __gnu_cxx::__numeric_traits<ptrdiff_t>::__max / sizeof(_Tp);
104 if (__len > __max)
105 __len = __max;
106
107 while (__len > 0)
108 {
109 _Tp* __tmp = static_cast<_Tp*>(::operator new(__len * sizeof(_Tp),
110 std::nothrow));
111 if (__tmp != 0)
112 return std::pair<_Tp*, ptrdiff_t>(__tmp, __len);
113 __len /= 2;
114 }
115 return std::pair<_Tp*, ptrdiff_t>(static_cast<_Tp*>(0), 0);
116 }
117
118 /**
119 * @brief The companion to get_temporary_buffer().
120 * @param __p A buffer previously allocated by get_temporary_buffer.
121 * @return None.
122 *
123 * Frees the memory pointed to by __p.
124 */
125 template<typename _Tp>
126 inline void
127 return_temporary_buffer(_Tp* __p)
128 { ::operator delete(__p); }
129
130 /**
131 * This class is used in two places: stl_algo.h and ext/memory,
132 * where it is wrapped as the temporary_buffer class. See
133 * temporary_buffer docs for more notes.
134 */
135 template<typename _ForwardIterator, typename _Tp>
136 class _Temporary_buffer
137 {
138 // concept requirements
139 __glibcxx_class_requires(_ForwardIterator, _ForwardIteratorConcept)
140
141 public:
142 typedef _Tp value_type;
143 typedef value_type* pointer;
144 typedef pointer iterator;
145 typedef ptrdiff_t size_type;
146
147 protected:
148 size_type _M_original_len;
149 size_type _M_len;
150 pointer _M_buffer;
151
152 public:
153 /// As per Table mumble.
154 size_type
155 size() const
156 { return _M_len; }
157
158 /// Returns the size requested by the constructor; may be >size().
159 size_type
160 requested_size() const
161 { return _M_original_len; }
162
163 /// As per Table mumble.
164 iterator
165 begin()
166 { return _M_buffer; }
167
168 /// As per Table mumble.
169 iterator
170 end()
171 { return _M_buffer + _M_len; }
172
173 /**
174 * Constructs a temporary buffer of a size somewhere between
175 * zero and the given length.
176 */
177 _Temporary_buffer(_ForwardIterator __seed, size_type __original_len);
178
179 ~_Temporary_buffer()
180 {
181 std::_Destroy(_M_buffer, _M_buffer + _M_len);
182 std::__detail::__return_temporary_buffer(_M_buffer, _M_len);
183 }
184
185 private:
186 // Disable copy constructor and assignment operator.
187 _Temporary_buffer(const _Temporary_buffer&);
188
189 void
190 operator=(const _Temporary_buffer&);
191 };
192
193
194 template<bool>
195 struct __uninitialized_construct_buf_dispatch
196 {
197 template<typename _Pointer, typename _ForwardIterator>
198 static void
199 __ucr(_Pointer __first, _Pointer __last,
200 _ForwardIterator __seed)
201 {
202 if (__first == __last)
203 return;
204
205 _Pointer __cur = __first;
206 __try
207 {
208 std::_Construct(std::__addressof(*__first),
209 _GLIBCXX_MOVE(*__seed));
210 _Pointer __prev = __cur;
211 ++__cur;
212 for(; __cur != __last; ++__cur, ++__prev)
213 std::_Construct(std::__addressof(*__cur),
214 _GLIBCXX_MOVE(*__prev));
215 *__seed = _GLIBCXX_MOVE(*__prev);
216 }
217 __catch(...)
218 {
219 std::_Destroy(__first, __cur);
220 __throw_exception_again;
221 }
222 }
223 };
224
225 template<>
226 struct __uninitialized_construct_buf_dispatch<true>
227 {
228 template<typename _Pointer, typename _ForwardIterator>
229 static void
230 __ucr(_Pointer, _Pointer, _ForwardIterator) { }
231 };
232
233 // Constructs objects in the range [first, last).
234 // Note that while these new objects will take valid values,
235 // their exact value is not defined. In particular they may
236 // be 'moved from'.
237 //
238 // While *__seed may be altered during this algorithm, it will have
239 // the same value when the algorithm finishes, unless one of the
240 // constructions throws.
241 //
242 // Requirements: _Pointer::value_type(_Tp&&) is valid.
243 template<typename _Pointer, typename _ForwardIterator>
244 inline void
245 __uninitialized_construct_buf(_Pointer __first, _Pointer __last,
246 _ForwardIterator __seed)
247 {
248 typedef typename std::iterator_traits<_Pointer>::value_type
249 _ValueType;
250
251 std::__uninitialized_construct_buf_dispatch<
252 __has_trivial_constructor(_ValueType)>::
253 __ucr(__first, __last, __seed);
254 }
255
256 template<typename _ForwardIterator, typename _Tp>
257 _Temporary_buffer<_ForwardIterator, _Tp>::
258 _Temporary_buffer(_ForwardIterator __seed, size_type __original_len)
259 : _M_original_len(__original_len), _M_len(0), _M_buffer(0)
260 {
261 std::pair<pointer, size_type> __p(
262 std::get_temporary_buffer<value_type>(_M_original_len));
263
264 if (__p.first)
265 {
266 __try
267 {
268 std::__uninitialized_construct_buf(__p.first, __p.first + __p.second,
269 __seed);
270 _M_buffer = __p.first;
271 _M_len = __p.second;
272 }
273 __catch(...)
274 {
275 std::__detail::__return_temporary_buffer(__p.first, __p.second);
276 __throw_exception_again;
277 }
278 }
279 }
280
281 _GLIBCXX_END_NAMESPACE_VERSION
282 } // namespace
283
284 #endif /* _STL_TEMPBUF_H */
285