xref: /netbsd-src/external/gpl3/gcc.old/dist/libstdc++-v3/include/ext/rc_string_base.h (revision 8feb0f0b7eaff0608f8350bbfa3098827b4bb91b)
1 // Reference-counted versatile string base -*- C++ -*-
2 
3 // Copyright (C) 2005-2020 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 /** @file ext/rc_string_base.h
26  *  This is an internal header file, included by other library headers.
27  *  Do not attempt to use it directly. @headername{ext/vstring.h}
28  */
29 
30 #ifndef _RC_STRING_BASE_H
31 #define _RC_STRING_BASE_H 1
32 
33 #include <ext/atomicity.h>
34 #include <ext/alloc_traits.h>
35 #include <bits/stl_iterator_base_funcs.h>
36 
_GLIBCXX_VISIBILITY(default)37 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
38 {
39 _GLIBCXX_BEGIN_NAMESPACE_VERSION
40 
41   /**
42    *  Documentation?  What's that?
43    *  Nathan Myers <ncm@cantrip.org>.
44    *
45    *  A string looks like this:
46    *
47    *  @code
48    *                                        [_Rep]
49    *                                        _M_length
50    *   [__rc_string_base<char_type>]        _M_capacity
51    *   _M_dataplus                          _M_refcount
52    *   _M_p ---------------->               unnamed array of char_type
53    *  @endcode
54    *
55    *  Where the _M_p points to the first character in the string, and
56    *  you cast it to a pointer-to-_Rep and subtract 1 to get a
57    *  pointer to the header.
58    *
59    *  This approach has the enormous advantage that a string object
60    *  requires only one allocation.  All the ugliness is confined
61    *  within a single pair of inline functions, which each compile to
62    *  a single @a add instruction: _Rep::_M_refdata(), and
63    *  __rc_string_base::_M_rep(); and the allocation function which gets a
64    *  block of raw bytes and with room enough and constructs a _Rep
65    *  object at the front.
66    *
67    *  The reason you want _M_data pointing to the character array and
68    *  not the _Rep is so that the debugger can see the string
69    *  contents. (Probably we should add a non-inline member to get
70    *  the _Rep for the debugger to use, so users can check the actual
71    *  string length.)
72    *
73    *  Note that the _Rep object is a POD so that you can have a
74    *  static <em>empty string</em> _Rep object already @a constructed before
75    *  static constructors have run.  The reference-count encoding is
76    *  chosen so that a 0 indicates one reference, so you never try to
77    *  destroy the empty-string _Rep object.
78    *
79    *  All but the last paragraph is considered pretty conventional
80    *  for a C++ string implementation.
81   */
82  template<typename _CharT, typename _Traits, typename _Alloc>
83     class __rc_string_base
84     : protected __vstring_utility<_CharT, _Traits, _Alloc>
85     {
86     public:
87       typedef _Traits					    traits_type;
88       typedef typename _Traits::char_type		    value_type;
89       typedef _Alloc					    allocator_type;
90 
91       typedef __vstring_utility<_CharT, _Traits, _Alloc>    _Util_Base;
92       typedef typename _Util_Base::_CharT_alloc_type        _CharT_alloc_type;
93       typedef typename _CharT_alloc_type::size_type	    size_type;
94 
95     private:
96       // _Rep: string representation
97       //   Invariants:
98       //   1. String really contains _M_length + 1 characters: due to 21.3.4
99       //      must be kept null-terminated.
100       //   2. _M_capacity >= _M_length
101       //      Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
102       //   3. _M_refcount has three states:
103       //      -1: leaked, one reference, no ref-copies allowed, non-const.
104       //       0: one reference, non-const.
105       //     n>0: n + 1 references, operations require a lock, const.
106       //   4. All fields == 0 is an empty string, given the extra storage
107       //      beyond-the-end for a null terminator; thus, the shared
108       //      empty string representation needs no constructor.
109       struct _Rep
110       {
111 	union
112 	{
113 	  struct
114 	  {
115 	    size_type	    _M_length;
116 	    size_type	    _M_capacity;
117 	    _Atomic_word    _M_refcount;
118 	  }                 _M_info;
119 
120 	  // Only for alignment purposes.
121 	  _CharT            _M_align;
122 	};
123 
124 	typedef typename __alloc_traits<_Alloc>::template rebind<_Rep>::other
125 	  _Rep_alloc_type;
126 
127  	_CharT*
128 	_M_refdata() throw()
129 	{ return reinterpret_cast<_CharT*>(this + 1); }
130 
131 	_CharT*
132 	_M_refcopy() throw()
133 	{
134 	  __atomic_add_dispatch(&_M_info._M_refcount, 1);
135 	  return _M_refdata();
136 	}  // XXX MT
137 
138 	void
139 	_M_set_length(size_type __n)
140 	{
141 	  _M_info._M_refcount = 0;  // One reference.
142 	  _M_info._M_length = __n;
143 	  // grrr. (per 21.3.4)
144 	  // You cannot leave those LWG people alone for a second.
145 	  traits_type::assign(_M_refdata()[__n], _CharT());
146 	}
147 
148 	// Create & Destroy
149 	static _Rep*
150 	_S_create(size_type, size_type, const _Alloc&);
151 
152 	void
153 	_M_destroy(const _Alloc&) throw();
154 
155 	_CharT*
156 	_M_clone(const _Alloc&, size_type __res = 0);
157       };
158 
159       struct _Rep_empty
160       : public _Rep
161       {
162 	_CharT              _M_terminal;
163       };
164 
165       static _Rep_empty     _S_empty_rep;
166 
167       // The maximum number of individual char_type elements of an
168       // individual string is determined by _S_max_size. This is the
169       // value that will be returned by max_size().  (Whereas npos
170       // is the maximum number of bytes the allocator can allocate.)
171       // If one was to divvy up the theoretical largest size string,
172       // with a terminating character and m _CharT elements, it'd
173       // look like this:
174       // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
175       //        + sizeof(_Rep) - 1
176       // (NB: last two terms for rounding reasons, see _M_create below)
177       // Solving for m:
178       // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
179       // In addition, this implementation halves this amount.
180       enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)
181 			      + 1) / sizeof(_CharT)) - 1) / 2 };
182 
183       // Data Member (private):
184       mutable typename _Util_Base::template _Alloc_hider<_Alloc>  _M_dataplus;
185 
186       void
187       _M_data(_CharT* __p)
188       { _M_dataplus._M_p = __p; }
189 
190       _Rep*
191       _M_rep() const
192       { return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }
193 
194       _CharT*
195       _M_grab(const _Alloc& __alloc) const
196       {
197 	return (!_M_is_leaked() && _M_get_allocator() == __alloc)
198 		? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);
199       }
200 
201       void
202       _M_dispose()
203       {
204 	// Be race-detector-friendly.  For more info see bits/c++config.
205 	_GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_rep()->_M_info.
206 						_M_refcount);
207 	if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
208 					-1) <= 0)
209 	  {
210 	    _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_rep()->_M_info.
211 						   _M_refcount);
212 	    _M_rep()->_M_destroy(_M_get_allocator());
213 	  }
214       }  // XXX MT
215 
216       bool
217       _M_is_leaked() const
218       { return _M_rep()->_M_info._M_refcount < 0; }
219 
220       void
221       _M_set_sharable()
222       { _M_rep()->_M_info._M_refcount = 0; }
223 
224       void
225       _M_leak_hard();
226 
227       // _S_construct_aux is used to implement the 21.3.1 para 15 which
228       // requires special behaviour if _InIterator is an integral type
229       template<typename _InIterator>
230 	static _CharT*
231 	_S_construct_aux(_InIterator __beg, _InIterator __end,
232 			 const _Alloc& __a, std::__false_type)
233 	{
234 	  typedef typename std::iterator_traits<_InIterator>::iterator_category
235 	    _Tag;
236 	  return _S_construct(__beg, __end, __a, _Tag());
237 	}
238 
239       // _GLIBCXX_RESOLVE_LIB_DEFECTS
240       // 438. Ambiguity in the "do the right thing" clause
241       template<typename _Integer>
242 	static _CharT*
243 	_S_construct_aux(_Integer __beg, _Integer __end,
244 			 const _Alloc& __a, std::__true_type)
245 	{ return _S_construct_aux_2(static_cast<size_type>(__beg),
246 				    __end, __a); }
247 
248       static _CharT*
249       _S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)
250       { return _S_construct(__req, __c, __a); }
251 
252       template<typename _InIterator>
253 	static _CharT*
254 	_S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
255 	{
256 	  typedef typename std::__is_integer<_InIterator>::__type _Integral;
257 	  return _S_construct_aux(__beg, __end, __a, _Integral());
258 	}
259 
260       // For Input Iterators, used in istreambuf_iterators, etc.
261       template<typename _InIterator>
262 	static _CharT*
263 	 _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
264 		      std::input_iterator_tag);
265 
266       // For forward_iterators up to random_access_iterators, used for
267       // string::iterator, _CharT*, etc.
268       template<typename _FwdIterator>
269 	static _CharT*
270 	_S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
271 		     std::forward_iterator_tag);
272 
273       static _CharT*
274       _S_construct(size_type __req, _CharT __c, const _Alloc& __a);
275 
276     public:
277       size_type
278       _M_max_size() const
279       { return size_type(_S_max_size); }
280 
281       _CharT*
282       _M_data() const
283       { return _M_dataplus._M_p; }
284 
285       size_type
286       _M_length() const
287       { return _M_rep()->_M_info._M_length; }
288 
289       size_type
290       _M_capacity() const
291       { return _M_rep()->_M_info._M_capacity; }
292 
293       bool
294       _M_is_shared() const
295       { return _M_rep()->_M_info._M_refcount > 0; }
296 
297       void
298       _M_set_leaked()
299       { _M_rep()->_M_info._M_refcount = -1; }
300 
301       void
302       _M_leak()    // for use in begin() & non-const op[]
303       {
304 	if (!_M_is_leaked())
305 	  _M_leak_hard();
306       }
307 
308       void
309       _M_set_length(size_type __n)
310       { _M_rep()->_M_set_length(__n); }
311 
312       __rc_string_base()
313       : _M_dataplus(_S_empty_rep._M_refcopy()) { }
314 
315       __rc_string_base(const _Alloc& __a);
316 
317       __rc_string_base(const __rc_string_base& __rcs);
318 
319 #if __cplusplus >= 201103L
320       __rc_string_base(__rc_string_base&& __rcs)
321       : _M_dataplus(__rcs._M_dataplus)
322       { __rcs._M_data(_S_empty_rep._M_refcopy()); }
323 #endif
324 
325       __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
326 
327       template<typename _InputIterator>
328 	__rc_string_base(_InputIterator __beg, _InputIterator __end,
329 			 const _Alloc& __a);
330 
331       ~__rc_string_base()
332       { _M_dispose(); }
333 
334       allocator_type&
335       _M_get_allocator()
336       { return _M_dataplus; }
337 
338       const allocator_type&
339       _M_get_allocator() const
340       { return _M_dataplus; }
341 
342       void
343       _M_swap(__rc_string_base& __rcs);
344 
345       void
346       _M_assign(const __rc_string_base& __rcs);
347 
348       void
349       _M_reserve(size_type __res);
350 
351       void
352       _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
353 		size_type __len2);
354 
355       void
356       _M_erase(size_type __pos, size_type __n);
357 
358       void
359       _M_clear()
360       {
361 	_M_dispose();
362 	_M_data(_S_empty_rep._M_refcopy());
363       }
364 
365       bool
366       _M_compare(const __rc_string_base&) const
367       { return false; }
368     };
369 
370   template<typename _CharT, typename _Traits, typename _Alloc>
371     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep_empty
372     __rc_string_base<_CharT, _Traits, _Alloc>::_S_empty_rep;
373 
374   template<typename _CharT, typename _Traits, typename _Alloc>
375     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep*
376     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
377     _S_create(size_type __capacity, size_type __old_capacity,
378 	      const _Alloc& __alloc)
379     {
380       // _GLIBCXX_RESOLVE_LIB_DEFECTS
381       // 83.  String::npos vs. string::max_size()
382       if (__capacity > size_type(_S_max_size))
383 	std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
384 
385       // The standard places no restriction on allocating more memory
386       // than is strictly needed within this layer at the moment or as
387       // requested by an explicit application call to reserve().
388 
389       // Many malloc implementations perform quite poorly when an
390       // application attempts to allocate memory in a stepwise fashion
391       // growing each allocation size by only 1 char.  Additionally,
392       // it makes little sense to allocate less linear memory than the
393       // natural blocking size of the malloc implementation.
394       // Unfortunately, we would need a somewhat low-level calculation
395       // with tuned parameters to get this perfect for any particular
396       // malloc implementation.  Fortunately, generalizations about
397       // common features seen among implementations seems to suffice.
398 
399       // __pagesize need not match the actual VM page size for good
400       // results in practice, thus we pick a common value on the low
401       // side.  __malloc_header_size is an estimate of the amount of
402       // overhead per memory allocation (in practice seen N * sizeof
403       // (void*) where N is 0, 2 or 4).  According to folklore,
404       // picking this value on the high side is better than
405       // low-balling it (especially when this algorithm is used with
406       // malloc implementations that allocate memory blocks rounded up
407       // to a size which is a power of 2).
408       const size_type __pagesize = 4096;
409       const size_type __malloc_header_size = 4 * sizeof(void*);
410 
411       // The below implements an exponential growth policy, necessary to
412       // meet amortized linear time requirements of the library: see
413       // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
414       if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
415 	{
416 	  __capacity = 2 * __old_capacity;
417 	  // Never allocate a string bigger than _S_max_size.
418 	  if (__capacity > size_type(_S_max_size))
419 	    __capacity = size_type(_S_max_size);
420 	}
421 
422       // NB: Need an array of char_type[__capacity], plus a terminating
423       // null char_type() element, plus enough for the _Rep data structure,
424       // plus sizeof(_Rep) - 1 to upper round to a size multiple of
425       // sizeof(_Rep).
426       // Whew. Seemingly so needy, yet so elemental.
427       size_type __size = ((__capacity + 1) * sizeof(_CharT)
428 			  + 2 * sizeof(_Rep) - 1);
429 
430       const size_type __adj_size = __size + __malloc_header_size;
431       if (__adj_size > __pagesize && __capacity > __old_capacity)
432 	{
433 	  const size_type __extra = __pagesize - __adj_size % __pagesize;
434 	  __capacity += __extra / sizeof(_CharT);
435 	  if (__capacity > size_type(_S_max_size))
436 	    __capacity = size_type(_S_max_size);
437 	  __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
438 	}
439 
440       // NB: Might throw, but no worries about a leak, mate: _Rep()
441       // does not throw.
442       _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
443       _Rep* __p = new (__place) _Rep;
444       __p->_M_info._M_capacity = __capacity;
445       return __p;
446     }
447 
448   template<typename _CharT, typename _Traits, typename _Alloc>
449     void
450     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
451     _M_destroy(const _Alloc& __a) throw ()
452     {
453       const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
454 				+ 2 * sizeof(_Rep) - 1);
455       _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
456     }
457 
458   template<typename _CharT, typename _Traits, typename _Alloc>
459     _CharT*
460     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
461     _M_clone(const _Alloc& __alloc, size_type __res)
462     {
463       // Requested capacity of the clone.
464       const size_type __requested_cap = _M_info._M_length + __res;
465       _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
466 				  __alloc);
467 
468       if (_M_info._M_length)
469 	__rc_string_base::_S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
470 
471       __r->_M_set_length(_M_info._M_length);
472       return __r->_M_refdata();
473     }
474 
475   template<typename _CharT, typename _Traits, typename _Alloc>
476     __rc_string_base<_CharT, _Traits, _Alloc>::
477     __rc_string_base(const _Alloc& __a)
478     : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
479 
480   template<typename _CharT, typename _Traits, typename _Alloc>
481     __rc_string_base<_CharT, _Traits, _Alloc>::
482     __rc_string_base(const __rc_string_base& __rcs)
483     : _M_dataplus(__rcs._M_get_allocator(),
484 		  __rcs._M_grab(__rcs._M_get_allocator())) { }
485 
486   template<typename _CharT, typename _Traits, typename _Alloc>
487     __rc_string_base<_CharT, _Traits, _Alloc>::
488     __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
489     : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
490 
491   template<typename _CharT, typename _Traits, typename _Alloc>
492     template<typename _InputIterator>
493     __rc_string_base<_CharT, _Traits, _Alloc>::
494     __rc_string_base(_InputIterator __beg, _InputIterator __end,
495 		     const _Alloc& __a)
496     : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
497 
498   template<typename _CharT, typename _Traits, typename _Alloc>
499     void
500     __rc_string_base<_CharT, _Traits, _Alloc>::
501     _M_leak_hard()
502     {
503       if (_M_is_shared())
504 	_M_erase(0, 0);
505       _M_set_leaked();
506     }
507 
508   // NB: This is the special case for Input Iterators, used in
509   // istreambuf_iterators, etc.
510   // Input Iterators have a cost structure very different from
511   // pointers, calling for a different coding style.
512   template<typename _CharT, typename _Traits, typename _Alloc>
513     template<typename _InIterator>
514       _CharT*
515       __rc_string_base<_CharT, _Traits, _Alloc>::
516       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
517 		   std::input_iterator_tag)
518       {
519 	if (__beg == __end && __a == _Alloc())
520 	  return _S_empty_rep._M_refcopy();
521 
522 	// Avoid reallocation for common case.
523 	_CharT __buf[128];
524 	size_type __len = 0;
525 	while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
526 	  {
527 	    __buf[__len++] = *__beg;
528 	    ++__beg;
529 	  }
530 	_Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
531 	_S_copy(__r->_M_refdata(), __buf, __len);
532 	__try
533 	  {
534 	    while (__beg != __end)
535 	      {
536 		if (__len == __r->_M_info._M_capacity)
537 		  {
538 		    // Allocate more space.
539 		    _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
540 		    _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
541 		    __r->_M_destroy(__a);
542 		    __r = __another;
543 		  }
544 		__r->_M_refdata()[__len++] = *__beg;
545 		++__beg;
546 	      }
547 	  }
548 	__catch(...)
549 	  {
550 	    __r->_M_destroy(__a);
551 	    __throw_exception_again;
552 	  }
553 	__r->_M_set_length(__len);
554 	return __r->_M_refdata();
555       }
556 
557   template<typename _CharT, typename _Traits, typename _Alloc>
558     template<typename _InIterator>
559       _CharT*
560       __rc_string_base<_CharT, _Traits, _Alloc>::
561       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
562 		   std::forward_iterator_tag)
563       {
564 	if (__beg == __end && __a == _Alloc())
565 	  return _S_empty_rep._M_refcopy();
566 
567 	// NB: Not required, but considered best practice.
568 	if (__is_null_pointer(__beg) && __beg != __end)
569 	  std::__throw_logic_error(__N("__rc_string_base::"
570 				       "_S_construct null not valid"));
571 
572 	const size_type __dnew = static_cast<size_type>(std::distance(__beg,
573 								      __end));
574 	// Check for out_of_range and length_error exceptions.
575 	_Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
576 	__try
577 	  { __rc_string_base::_S_copy_chars(__r->_M_refdata(), __beg, __end); }
578 	__catch(...)
579 	  {
580 	    __r->_M_destroy(__a);
581 	    __throw_exception_again;
582 	  }
583 	__r->_M_set_length(__dnew);
584 	return __r->_M_refdata();
585       }
586 
587   template<typename _CharT, typename _Traits, typename _Alloc>
588     _CharT*
589     __rc_string_base<_CharT, _Traits, _Alloc>::
590     _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
591     {
592       if (__n == 0 && __a == _Alloc())
593 	return _S_empty_rep._M_refcopy();
594 
595       // Check for out_of_range and length_error exceptions.
596       _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
597       if (__n)
598 	__rc_string_base::_S_assign(__r->_M_refdata(), __n, __c);
599 
600       __r->_M_set_length(__n);
601       return __r->_M_refdata();
602     }
603 
604   template<typename _CharT, typename _Traits, typename _Alloc>
605     void
606     __rc_string_base<_CharT, _Traits, _Alloc>::
607     _M_swap(__rc_string_base& __rcs)
608     {
609       if (_M_is_leaked())
610 	_M_set_sharable();
611       if (__rcs._M_is_leaked())
612 	__rcs._M_set_sharable();
613 
614       _CharT* __tmp = _M_data();
615       _M_data(__rcs._M_data());
616       __rcs._M_data(__tmp);
617 
618       // _GLIBCXX_RESOLVE_LIB_DEFECTS
619       // 431. Swapping containers with unequal allocators.
620       std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
621 						  __rcs._M_get_allocator());
622     }
623 
624   template<typename _CharT, typename _Traits, typename _Alloc>
625     void
626     __rc_string_base<_CharT, _Traits, _Alloc>::
627     _M_assign(const __rc_string_base& __rcs)
628     {
629       if (_M_rep() != __rcs._M_rep())
630 	{
631 	  _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
632 	  _M_dispose();
633 	  _M_data(__tmp);
634 	}
635     }
636 
637   template<typename _CharT, typename _Traits, typename _Alloc>
638     void
639     __rc_string_base<_CharT, _Traits, _Alloc>::
640     _M_reserve(size_type __res)
641     {
642       // Make sure we don't shrink below the current size.
643       if (__res < _M_length())
644 	__res = _M_length();
645 
646       if (__res != _M_capacity() || _M_is_shared())
647 	{
648 	  _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
649 					     __res - _M_length());
650 	  _M_dispose();
651 	  _M_data(__tmp);
652 	}
653     }
654 
655   template<typename _CharT, typename _Traits, typename _Alloc>
656     void
657     __rc_string_base<_CharT, _Traits, _Alloc>::
658     _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
659 	      size_type __len2)
660     {
661       const size_type __how_much = _M_length() - __pos - __len1;
662 
663       _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
664 				  _M_capacity(), _M_get_allocator());
665 
666       if (__pos)
667 	this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
668       if (__s && __len2)
669 	this->_S_copy(__r->_M_refdata() + __pos, __s, __len2);
670       if (__how_much)
671 	this->_S_copy(__r->_M_refdata() + __pos + __len2,
672 		_M_data() + __pos + __len1, __how_much);
673 
674       _M_dispose();
675       _M_data(__r->_M_refdata());
676     }
677 
678   template<typename _CharT, typename _Traits, typename _Alloc>
679     void
680     __rc_string_base<_CharT, _Traits, _Alloc>::
681     _M_erase(size_type __pos, size_type __n)
682     {
683       const size_type __new_size = _M_length() - __n;
684       const size_type __how_much = _M_length() - __pos - __n;
685 
686       if (_M_is_shared())
687 	{
688 	  // Must reallocate.
689 	  _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
690 				      _M_get_allocator());
691 
692 	  if (__pos)
693 	    this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
694 	  if (__how_much)
695 	    this->_S_copy(__r->_M_refdata() + __pos,
696 		    _M_data() + __pos + __n, __how_much);
697 
698 	  _M_dispose();
699 	  _M_data(__r->_M_refdata());
700 	}
701       else if (__how_much && __n)
702 	{
703 	  // Work in-place.
704 	  this->_S_move(_M_data() + __pos,
705 		  _M_data() + __pos + __n, __how_much);
706 	}
707 
708       _M_rep()->_M_set_length(__new_size);
709     }
710 
711   template<>
712     inline bool
713     __rc_string_base<char, std::char_traits<char>,
714 		     std::allocator<char> >::
715     _M_compare(const __rc_string_base& __rcs) const
716     {
717       if (_M_rep() == __rcs._M_rep())
718 	return true;
719       return false;
720     }
721 
722 #ifdef _GLIBCXX_USE_WCHAR_T
723   template<>
724     inline bool
725     __rc_string_base<wchar_t, std::char_traits<wchar_t>,
726 		     std::allocator<wchar_t> >::
727     _M_compare(const __rc_string_base& __rcs) const
728     {
729       if (_M_rep() == __rcs._M_rep())
730 	return true;
731       return false;
732     }
733 #endif
734 
735 _GLIBCXX_END_NAMESPACE_VERSION
736 } // namespace
737 
738 #endif /* _RC_STRING_BASE_H */
739