1// Temporary buffer implementation -*- C++ -*-
2
3// Copyright (C) 2001-2024 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 <new>
60#include <bits/exception_defines.h>
61#include <bits/stl_construct.h>
62#include <bits/stl_pair.h>
63#include <ext/numeric_traits.h>
64
65namespace std _GLIBCXX_VISIBILITY(default)
66{
67_GLIBCXX_BEGIN_NAMESPACE_VERSION
68
69#if __has_builtin(__builtin_operator_new) >= 201802L
70# define _GLIBCXX_OPERATOR_NEW __builtin_operator_new
71# define _GLIBCXX_OPERATOR_DELETE __builtin_operator_delete
72#else
73# define _GLIBCXX_OPERATOR_NEW ::operator new
74# define _GLIBCXX_OPERATOR_DELETE ::operator delete
75#endif
76
77 namespace __detail
78 {
79 // Equivalent to std::get_temporary_buffer but won't return a smaller size.
80 // It either returns a buffer of __len elements, or a null pointer.
81 template<typename _Tp>
82 inline _Tp*
83 __get_temporary_buffer(ptrdiff_t __len) _GLIBCXX_NOTHROW
84 {
85 if (__builtin_expect(size_t(__len) > (size_t(-1) / sizeof(_Tp)), 0))
86 return 0;
87
88#if __cpp_aligned_new && __cplusplus >= 201103L
89 if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
90 return (_Tp*) _GLIBCXX_OPERATOR_NEW(__len * sizeof(_Tp),
91 align_val_t(alignof(_Tp)),
92 nothrow_t());
93#endif
94 return (_Tp*) _GLIBCXX_OPERATOR_NEW(__len * sizeof(_Tp), nothrow_t());
95 }
96
97 // Equivalent to std::return_temporary_buffer but with a size argument.
98 // The size is the number of elements, not the number of bytes.
99 template<typename _Tp>
100 inline void
101 __return_temporary_buffer(_Tp* __p,
102 size_t __len __attribute__((__unused__)))
103 {
104#if __cpp_sized_deallocation
105# define _GLIBCXX_SIZED_DEALLOC(T, p, n) (p), (n) * sizeof(T)
106#else
107# define _GLIBCXX_SIZED_DEALLOC(T, p, n) (p)
108#endif
109
110#if __cpp_aligned_new && __cplusplus >= 201103L
111 if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
112 {
113 _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(_Tp, __p, __len),
114 align_val_t(alignof(_Tp)));
115 return;
116 }
117#endif
118 _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(_Tp, __p, __len));
119 }
120#undef _GLIBCXX_SIZED_DEALLOC
121 }
122
123 /**
124 * @brief Allocates a temporary buffer.
125 * @param __len The number of objects of type Tp.
126 * @return See full description.
127 *
128 * Reinventing the wheel, but this time with prettier spokes!
129 *
130 * This function tries to obtain storage for @c __len adjacent Tp
131 * objects. The objects themselves are not constructed, of course.
132 * A pair<> is returned containing <em>the buffer's address and
133 * capacity (in the units of sizeof(_Tp)), or a pair of 0 values if
134 * no storage can be obtained.</em> Note that the capacity obtained
135 * may be less than that requested if the memory is unavailable;
136 * you should compare len with the .second return value.
137 *
138 * Provides the nothrow exception guarantee.
139 */
140 template<typename _Tp>
141 _GLIBCXX17_DEPRECATED
142 pair<_Tp*, ptrdiff_t>
143 get_temporary_buffer(ptrdiff_t __len) _GLIBCXX_NOEXCEPT
144 {
145 const ptrdiff_t __max =
146 __gnu_cxx::__numeric_traits<ptrdiff_t>::__max / sizeof(_Tp);
147 if (__len > __max)
148 __len = __max;
149
150 while (__len > 0)
151 {
152 if (_Tp* __tmp = __detail::__get_temporary_buffer<_Tp>(__len))
153 return pair<_Tp*, ptrdiff_t>(__tmp, __len);
154 __len = __len == 1 ? 0 : ((__len + 1) / 2);
155 }
156 return pair<_Tp*, ptrdiff_t>();
157 }
158
159 /**
160 * @brief The companion to get_temporary_buffer().
161 * @param __p A buffer previously allocated by get_temporary_buffer.
162 * @return None.
163 *
164 * Frees the memory pointed to by __p.
165 */
166 template<typename _Tp>
167 _GLIBCXX17_DEPRECATED
168 inline void
169 return_temporary_buffer(_Tp* __p)
170 {
171#if __cpp_aligned_new && __cplusplus >= 201103L
172 if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
173 _GLIBCXX_OPERATOR_DELETE(__p, align_val_t(alignof(_Tp)));
174 else
175#endif
176 _GLIBCXX_OPERATOR_DELETE(__p);
177 }
178
179#undef _GLIBCXX_OPERATOR_DELETE
180#undef _GLIBCXX_OPERATOR_NEW
181
182 /**
183 * This class is used in two places: stl_algo.h and ext/memory,
184 * where it is wrapped as the temporary_buffer class. See
185 * temporary_buffer docs for more notes.
186 */
187 template<typename _ForwardIterator, typename _Tp>
188 class _Temporary_buffer
189 {
190 // concept requirements
191 __glibcxx_class_requires(_ForwardIterator, _ForwardIteratorConcept)
192
193 public:
194 typedef _Tp value_type;
195 typedef value_type* pointer;
196 typedef pointer iterator;
197 typedef ptrdiff_t size_type;
198
199 protected:
200 size_type _M_original_len;
201 struct _Impl
202 {
203#pragma GCC diagnostic push
204#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
205 explicit
206 _Impl(ptrdiff_t __original_len)
207 {
208 pair<pointer, size_type> __p(
209 std::get_temporary_buffer<value_type>(__original_len));
210 _M_len = __p.second;
211 _M_buffer = __p.first;
212 }
213#pragma GCC diagnostic pop
214
215 ~_Impl()
216 { std::__detail::__return_temporary_buffer(_M_buffer, _M_len); }
217
218 size_type _M_len;
219 pointer _M_buffer;
220 } _M_impl;
221
222 public:
223 /// As per Table mumble.
224 size_type
225 size() const
226 { return _M_impl._M_len; }
227
228 /// Returns the size requested by the constructor; may be >size().
229 size_type
230 requested_size() const
231 { return _M_original_len; }
232
233 /// As per Table mumble.
234 iterator
235 begin()
236 { return _M_impl._M_buffer; }
237
238 /// As per Table mumble.
239 iterator
240 end()
241 { return _M_impl._M_buffer + _M_impl._M_len; }
242
243 /**
244 * Constructs a temporary buffer of a size somewhere between
245 * zero and the given length.
246 */
247 _Temporary_buffer(_ForwardIterator __seed, size_type __original_len);
248
249 ~_Temporary_buffer()
250 { std::_Destroy(_M_impl._M_buffer, _M_impl._M_buffer + _M_impl._M_len); }
251
252 private:
253 // Disable copy constructor and assignment operator.
254 _Temporary_buffer(const _Temporary_buffer&);
255
256 void
257 operator=(const _Temporary_buffer&);
258 };
259
260
261 template<bool>
262 struct __uninitialized_construct_buf_dispatch
263 {
264 template<typename _Pointer, typename _ForwardIterator>
265 static void
266 __ucr(_Pointer __first, _Pointer __last,
267 _ForwardIterator __seed)
268 {
269 if (__builtin_expect(__first == __last, 0))
270 return;
271
272 _Pointer __cur = __first;
273 __try
274 {
275 std::_Construct(std::__addressof(*__first),
276 _GLIBCXX_MOVE(*__seed));
277 _Pointer __prev = __cur;
278 ++__cur;
279 for(; __cur != __last; ++__cur, ++__prev)
280 std::_Construct(std::__addressof(*__cur),
281 _GLIBCXX_MOVE(*__prev));
282 *__seed = _GLIBCXX_MOVE(*__prev);
283 }
284 __catch(...)
285 {
286 std::_Destroy(__first, __cur);
287 __throw_exception_again;
288 }
289 }
290 };
291
292 template<>
293 struct __uninitialized_construct_buf_dispatch<true>
294 {
295 template<typename _Pointer, typename _ForwardIterator>
296 static void
297 __ucr(_Pointer, _Pointer, _ForwardIterator) { }
298 };
299
300 // Constructs objects in the range [first, last).
301 // Note that while these new objects will take valid values,
302 // their exact value is not defined. In particular they may
303 // be 'moved from'.
304 //
305 // While *__seed may be altered during this algorithm, it will have
306 // the same value when the algorithm finishes, unless one of the
307 // constructions throws.
308 //
309 // Requirements:
310 // _Tp is move constructible and constructible from std::move(*__seed).
311 template<typename _Tp, typename _ForwardIterator>
312 inline void
313 __uninitialized_construct_buf(_Tp* __first, _Tp* __last,
314 _ForwardIterator __seed)
315 {
316 std::__uninitialized_construct_buf_dispatch<
317 __has_trivial_constructor(_Tp)>::
318 __ucr(__first, __last, __seed);
319 }
320
321 template<typename _ForwardIterator, typename _Tp>
322 _Temporary_buffer<_ForwardIterator, _Tp>::
323 _Temporary_buffer(_ForwardIterator __seed, size_type __original_len)
324 : _M_original_len(__original_len), _M_impl(__original_len)
325 {
326 std::__uninitialized_construct_buf(begin(), end(), __seed);
327 }
328
329_GLIBCXX_END_NAMESPACE_VERSION
330} // namespace
331
332#endif /* _STL_TEMPBUF_H */
333