rc_string_base.h

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00001 // Reference-counted versatile string base -*- C++ -*-
00002 
00003 // Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010
00004 // Free Software Foundation, Inc.
00005 //
00006 // This file is part of the GNU ISO C++ Library.  This library is free
00007 // software; you can redistribute it and/or modify it under the
00008 // terms of the GNU General Public License as published by the
00009 // Free Software Foundation; either version 3, or (at your option)
00010 // any later version.
00011 
00012 // This library is distributed in the hope that it will be useful,
00013 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00014 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00015 // GNU General Public License for more details.
00016 
00017 // Under Section 7 of GPL version 3, you are granted additional
00018 // permissions described in the GCC Runtime Library Exception, version
00019 // 3.1, as published by the Free Software Foundation.
00020 
00021 // You should have received a copy of the GNU General Public License and
00022 // a copy of the GCC Runtime Library Exception along with this program;
00023 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00024 // <http://www.gnu.org/licenses/>.
00025 
00026 /** @file ext/rc_string_base.h
00027  *  This file is a GNU extension to the Standard C++ Library.
00028  *  This is an internal header file, included by other library headers.
00029  *  You should not attempt to use it directly.
00030  */
00031 
00032 #ifndef _RC_STRING_BASE_H
00033 #define _RC_STRING_BASE_H 1
00034 
00035 #include <ext/atomicity.h>
00036 #include <bits/stl_iterator_base_funcs.h>
00037 
00038 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
00039 
00040   /**
00041    *  Documentation?  What's that?
00042    *  Nathan Myers <ncm@cantrip.org>.
00043    *
00044    *  A string looks like this:
00045    *
00046    *  @code
00047    *                                        [_Rep]
00048    *                                        _M_length
00049    *   [__rc_string_base<char_type>]        _M_capacity
00050    *   _M_dataplus                          _M_refcount
00051    *   _M_p ---------------->               unnamed array of char_type
00052    *  @endcode
00053    *
00054    *  Where the _M_p points to the first character in the string, and
00055    *  you cast it to a pointer-to-_Rep and subtract 1 to get a
00056    *  pointer to the header.
00057    *
00058    *  This approach has the enormous advantage that a string object
00059    *  requires only one allocation.  All the ugliness is confined
00060    *  within a single pair of inline functions, which each compile to
00061    *  a single @a add instruction: _Rep::_M_refdata(), and
00062    *  __rc_string_base::_M_rep(); and the allocation function which gets a
00063    *  block of raw bytes and with room enough and constructs a _Rep
00064    *  object at the front.
00065    *
00066    *  The reason you want _M_data pointing to the character array and
00067    *  not the _Rep is so that the debugger can see the string
00068    *  contents. (Probably we should add a non-inline member to get
00069    *  the _Rep for the debugger to use, so users can check the actual
00070    *  string length.)
00071    *
00072    *  Note that the _Rep object is a POD so that you can have a
00073    *  static <em>empty string</em> _Rep object already @a constructed before
00074    *  static constructors have run.  The reference-count encoding is
00075    *  chosen so that a 0 indicates one reference, so you never try to
00076    *  destroy the empty-string _Rep object.
00077    *
00078    *  All but the last paragraph is considered pretty conventional
00079    *  for a C++ string implementation.
00080   */
00081  template<typename _CharT, typename _Traits, typename _Alloc>
00082     class __rc_string_base
00083     : protected __vstring_utility<_CharT, _Traits, _Alloc>
00084     {
00085     public:
00086       typedef _Traits                       traits_type;
00087       typedef typename _Traits::char_type           value_type;
00088       typedef _Alloc                        allocator_type;
00089 
00090       typedef __vstring_utility<_CharT, _Traits, _Alloc>    _Util_Base;
00091       typedef typename _Util_Base::_CharT_alloc_type        _CharT_alloc_type;
00092       typedef typename _CharT_alloc_type::size_type     size_type;
00093 
00094     private:
00095       // _Rep: string representation
00096       //   Invariants:
00097       //   1. String really contains _M_length + 1 characters: due to 21.3.4
00098       //      must be kept null-terminated.
00099       //   2. _M_capacity >= _M_length
00100       //      Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
00101       //   3. _M_refcount has three states:
00102       //      -1: leaked, one reference, no ref-copies allowed, non-const.
00103       //       0: one reference, non-const.
00104       //     n>0: n + 1 references, operations require a lock, const.
00105       //   4. All fields == 0 is an empty string, given the extra storage
00106       //      beyond-the-end for a null terminator; thus, the shared
00107       //      empty string representation needs no constructor.
00108       struct _Rep
00109       {
00110     union
00111     {
00112       struct
00113       {
00114         size_type       _M_length;
00115         size_type       _M_capacity;
00116         _Atomic_word    _M_refcount;
00117       }                 _M_info;
00118       
00119       // Only for alignment purposes.
00120       _CharT            _M_align;
00121     };
00122 
00123     typedef typename _Alloc::template rebind<_Rep>::other _Rep_alloc_type;
00124 
00125     _CharT*
00126     _M_refdata() throw()
00127     { return reinterpret_cast<_CharT*>(this + 1); }
00128 
00129     _CharT*
00130     _M_refcopy() throw()
00131     {
00132       __atomic_add_dispatch(&_M_info._M_refcount, 1);
00133       return _M_refdata();
00134     }  // XXX MT
00135     
00136     void
00137     _M_set_length(size_type __n)
00138     { 
00139       _M_info._M_refcount = 0;  // One reference.
00140       _M_info._M_length = __n;
00141       // grrr. (per 21.3.4)
00142       // You cannot leave those LWG people alone for a second.
00143       traits_type::assign(_M_refdata()[__n], _CharT());
00144     }
00145 
00146     // Create & Destroy
00147     static _Rep*
00148     _S_create(size_type, size_type, const _Alloc&);
00149 
00150     void
00151     _M_destroy(const _Alloc&) throw();
00152 
00153     _CharT*
00154     _M_clone(const _Alloc&, size_type __res = 0);
00155       };
00156 
00157       struct _Rep_empty
00158       : public _Rep
00159       {
00160     _CharT              _M_terminal;
00161       };
00162 
00163       static _Rep_empty     _S_empty_rep;
00164 
00165       // The maximum number of individual char_type elements of an
00166       // individual string is determined by _S_max_size. This is the
00167       // value that will be returned by max_size().  (Whereas npos
00168       // is the maximum number of bytes the allocator can allocate.)
00169       // If one was to divvy up the theoretical largest size string,
00170       // with a terminating character and m _CharT elements, it'd
00171       // look like this:
00172       // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
00173       //        + sizeof(_Rep) - 1
00174       // (NB: last two terms for rounding reasons, see _M_create below)
00175       // Solving for m:
00176       // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
00177       // In addition, this implementation halves this amount.
00178       enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)
00179                   + 1) / sizeof(_CharT)) - 1) / 2 };
00180 
00181       // Data Member (private):
00182       mutable typename _Util_Base::template _Alloc_hider<_Alloc>  _M_dataplus;
00183 
00184       void
00185       _M_data(_CharT* __p)
00186       { _M_dataplus._M_p = __p; }
00187 
00188       _Rep*
00189       _M_rep() const
00190       { return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }
00191 
00192       _CharT*
00193       _M_grab(const _Alloc& __alloc) const
00194       {
00195     return (!_M_is_leaked() && _M_get_allocator() == __alloc)
00196             ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);
00197       }
00198 
00199       void
00200       _M_dispose()
00201       {
00202     if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
00203                     -1) <= 0)
00204       _M_rep()->_M_destroy(_M_get_allocator());
00205       }  // XXX MT
00206 
00207       bool
00208       _M_is_leaked() const
00209       { return _M_rep()->_M_info._M_refcount < 0; }
00210 
00211       void
00212       _M_set_sharable()
00213       { _M_rep()->_M_info._M_refcount = 0; }
00214 
00215       void
00216       _M_leak_hard();
00217 
00218       // _S_construct_aux is used to implement the 21.3.1 para 15 which
00219       // requires special behaviour if _InIterator is an integral type
00220       template<typename _InIterator>
00221         static _CharT*
00222         _S_construct_aux(_InIterator __beg, _InIterator __end,
00223              const _Alloc& __a, std::__false_type)
00224     {
00225           typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
00226           return _S_construct(__beg, __end, __a, _Tag());
00227     }
00228 
00229       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00230       // 438. Ambiguity in the "do the right thing" clause
00231       template<typename _Integer>
00232         static _CharT*
00233         _S_construct_aux(_Integer __beg, _Integer __end,
00234              const _Alloc& __a, std::__true_type)
00235     { return _S_construct_aux_2(static_cast<size_type>(__beg),
00236                     __end, __a); }
00237 
00238       static _CharT*
00239       _S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)
00240       { return _S_construct(__req, __c, __a); }
00241 
00242       template<typename _InIterator>
00243         static _CharT*
00244         _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
00245     {
00246       typedef typename std::__is_integer<_InIterator>::__type _Integral;
00247       return _S_construct_aux(__beg, __end, __a, _Integral());
00248         }
00249 
00250       // For Input Iterators, used in istreambuf_iterators, etc.
00251       template<typename _InIterator>
00252         static _CharT*
00253          _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
00254               std::input_iterator_tag);
00255       
00256       // For forward_iterators up to random_access_iterators, used for
00257       // string::iterator, _CharT*, etc.
00258       template<typename _FwdIterator>
00259         static _CharT*
00260         _S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
00261              std::forward_iterator_tag);
00262 
00263       static _CharT*
00264       _S_construct(size_type __req, _CharT __c, const _Alloc& __a);
00265 
00266     public:
00267       size_type
00268       _M_max_size() const
00269       { return size_type(_S_max_size); }
00270 
00271       _CharT*
00272       _M_data() const
00273       { return _M_dataplus._M_p; }
00274 
00275       size_type
00276       _M_length() const
00277       { return _M_rep()->_M_info._M_length; }
00278 
00279       size_type
00280       _M_capacity() const
00281       { return _M_rep()->_M_info._M_capacity; }
00282 
00283       bool
00284       _M_is_shared() const
00285       { return _M_rep()->_M_info._M_refcount > 0; }
00286 
00287       void
00288       _M_set_leaked()
00289       { _M_rep()->_M_info._M_refcount = -1; }
00290 
00291       void
00292       _M_leak()    // for use in begin() & non-const op[]
00293       {
00294     if (!_M_is_leaked())
00295       _M_leak_hard();
00296       }
00297 
00298       void
00299       _M_set_length(size_type __n)
00300       { _M_rep()->_M_set_length(__n); }
00301 
00302       __rc_string_base()
00303       : _M_dataplus(_S_empty_rep._M_refcopy()) { }
00304 
00305       __rc_string_base(const _Alloc& __a);
00306 
00307       __rc_string_base(const __rc_string_base& __rcs);
00308 
00309 #ifdef __GXX_EXPERIMENTAL_CXX0X__
00310       __rc_string_base(__rc_string_base&& __rcs)
00311       : _M_dataplus(__rcs._M_dataplus)
00312       { __rcs._M_data(_S_empty_rep._M_refcopy()); }
00313 #endif
00314 
00315       __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
00316 
00317       template<typename _InputIterator>
00318         __rc_string_base(_InputIterator __beg, _InputIterator __end,
00319              const _Alloc& __a);
00320 
00321       ~__rc_string_base()
00322       { _M_dispose(); }      
00323 
00324       allocator_type&
00325       _M_get_allocator()
00326       { return _M_dataplus; }
00327 
00328       const allocator_type&
00329       _M_get_allocator() const
00330       { return _M_dataplus; }
00331 
00332       void
00333       _M_swap(__rc_string_base& __rcs);
00334 
00335       void
00336       _M_assign(const __rc_string_base& __rcs);
00337 
00338       void
00339       _M_reserve(size_type __res);
00340 
00341       void
00342       _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
00343         size_type __len2);
00344       
00345       void
00346       _M_erase(size_type __pos, size_type __n);
00347 
00348       void
00349       _M_clear()
00350       { _M_erase(size_type(0), _M_length()); }
00351 
00352       bool
00353       _M_compare(const __rc_string_base&) const
00354       { return false; }
00355     };
00356 
00357   template<typename _CharT, typename _Traits, typename _Alloc>
00358     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep_empty
00359     __rc_string_base<_CharT, _Traits, _Alloc>::_S_empty_rep;
00360 
00361   template<typename _CharT, typename _Traits, typename _Alloc>
00362     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep*
00363     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00364     _S_create(size_type __capacity, size_type __old_capacity,
00365           const _Alloc& __alloc)
00366     {
00367       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00368       // 83.  String::npos vs. string::max_size()
00369       if (__capacity > size_type(_S_max_size))
00370     std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
00371 
00372       // The standard places no restriction on allocating more memory
00373       // than is strictly needed within this layer at the moment or as
00374       // requested by an explicit application call to reserve().
00375 
00376       // Many malloc implementations perform quite poorly when an
00377       // application attempts to allocate memory in a stepwise fashion
00378       // growing each allocation size by only 1 char.  Additionally,
00379       // it makes little sense to allocate less linear memory than the
00380       // natural blocking size of the malloc implementation.
00381       // Unfortunately, we would need a somewhat low-level calculation
00382       // with tuned parameters to get this perfect for any particular
00383       // malloc implementation.  Fortunately, generalizations about
00384       // common features seen among implementations seems to suffice.
00385 
00386       // __pagesize need not match the actual VM page size for good
00387       // results in practice, thus we pick a common value on the low
00388       // side.  __malloc_header_size is an estimate of the amount of
00389       // overhead per memory allocation (in practice seen N * sizeof
00390       // (void*) where N is 0, 2 or 4).  According to folklore,
00391       // picking this value on the high side is better than
00392       // low-balling it (especially when this algorithm is used with
00393       // malloc implementations that allocate memory blocks rounded up
00394       // to a size which is a power of 2).
00395       const size_type __pagesize = 4096;
00396       const size_type __malloc_header_size = 4 * sizeof(void*);
00397 
00398       // The below implements an exponential growth policy, necessary to
00399       // meet amortized linear time requirements of the library: see
00400       // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
00401       if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
00402     {
00403       __capacity = 2 * __old_capacity;
00404       // Never allocate a string bigger than _S_max_size.
00405       if (__capacity > size_type(_S_max_size))
00406         __capacity = size_type(_S_max_size);
00407     }
00408 
00409       // NB: Need an array of char_type[__capacity], plus a terminating
00410       // null char_type() element, plus enough for the _Rep data structure,
00411       // plus sizeof(_Rep) - 1 to upper round to a size multiple of
00412       // sizeof(_Rep).
00413       // Whew. Seemingly so needy, yet so elemental.
00414       size_type __size = ((__capacity + 1) * sizeof(_CharT)
00415               + 2 * sizeof(_Rep) - 1);
00416 
00417       const size_type __adj_size = __size + __malloc_header_size;
00418       if (__adj_size > __pagesize && __capacity > __old_capacity)
00419     {
00420       const size_type __extra = __pagesize - __adj_size % __pagesize;
00421       __capacity += __extra / sizeof(_CharT);
00422       if (__capacity > size_type(_S_max_size))
00423         __capacity = size_type(_S_max_size);
00424       __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
00425     }
00426 
00427       // NB: Might throw, but no worries about a leak, mate: _Rep()
00428       // does not throw.
00429       _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
00430       _Rep* __p = new (__place) _Rep;
00431       __p->_M_info._M_capacity = __capacity;
00432       return __p;
00433     }
00434 
00435   template<typename _CharT, typename _Traits, typename _Alloc>
00436     void
00437     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00438     _M_destroy(const _Alloc& __a) throw ()
00439     {
00440       const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
00441                 + 2 * sizeof(_Rep) - 1);
00442       _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
00443     }
00444 
00445   template<typename _CharT, typename _Traits, typename _Alloc>
00446     _CharT*
00447     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
00448     _M_clone(const _Alloc& __alloc, size_type __res)
00449     {
00450       // Requested capacity of the clone.
00451       const size_type __requested_cap = _M_info._M_length + __res;
00452       _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
00453                   __alloc);
00454 
00455       if (_M_info._M_length)
00456     _S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
00457 
00458       __r->_M_set_length(_M_info._M_length);
00459       return __r->_M_refdata();
00460     }
00461 
00462   template<typename _CharT, typename _Traits, typename _Alloc>
00463     __rc_string_base<_CharT, _Traits, _Alloc>::
00464     __rc_string_base(const _Alloc& __a)
00465     : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
00466 
00467   template<typename _CharT, typename _Traits, typename _Alloc>
00468     __rc_string_base<_CharT, _Traits, _Alloc>::
00469     __rc_string_base(const __rc_string_base& __rcs)
00470     : _M_dataplus(__rcs._M_get_allocator(),
00471           __rcs._M_grab(__rcs._M_get_allocator())) { }
00472 
00473   template<typename _CharT, typename _Traits, typename _Alloc>
00474     __rc_string_base<_CharT, _Traits, _Alloc>::
00475     __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
00476     : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
00477 
00478   template<typename _CharT, typename _Traits, typename _Alloc>
00479     template<typename _InputIterator>
00480     __rc_string_base<_CharT, _Traits, _Alloc>::
00481     __rc_string_base(_InputIterator __beg, _InputIterator __end,
00482              const _Alloc& __a)
00483     : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
00484 
00485   template<typename _CharT, typename _Traits, typename _Alloc>
00486     void
00487     __rc_string_base<_CharT, _Traits, _Alloc>::
00488     _M_leak_hard()
00489     {
00490       if (_M_is_shared())
00491     _M_erase(0, 0);
00492       _M_set_leaked();
00493     }
00494 
00495   // NB: This is the special case for Input Iterators, used in
00496   // istreambuf_iterators, etc.
00497   // Input Iterators have a cost structure very different from
00498   // pointers, calling for a different coding style.
00499   template<typename _CharT, typename _Traits, typename _Alloc>
00500     template<typename _InIterator>
00501       _CharT*
00502       __rc_string_base<_CharT, _Traits, _Alloc>::
00503       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
00504            std::input_iterator_tag)
00505       {
00506     if (__beg == __end && __a == _Alloc())
00507       return _S_empty_rep._M_refcopy();
00508 
00509     // Avoid reallocation for common case.
00510     _CharT __buf[128];
00511     size_type __len = 0;
00512     while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
00513       {
00514         __buf[__len++] = *__beg;
00515         ++__beg;
00516       }
00517     _Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
00518     _S_copy(__r->_M_refdata(), __buf, __len);
00519     __try
00520       {
00521         while (__beg != __end)
00522           {
00523         if (__len == __r->_M_info._M_capacity)
00524           {
00525             // Allocate more space.
00526             _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
00527             _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
00528             __r->_M_destroy(__a);
00529             __r = __another;
00530           }
00531         __r->_M_refdata()[__len++] = *__beg;
00532         ++__beg;
00533           }
00534       }
00535     __catch(...)
00536       {
00537         __r->_M_destroy(__a);
00538         __throw_exception_again;
00539       }
00540     __r->_M_set_length(__len);
00541     return __r->_M_refdata();
00542       }
00543 
00544   template<typename _CharT, typename _Traits, typename _Alloc>
00545     template<typename _InIterator>
00546       _CharT*
00547       __rc_string_base<_CharT, _Traits, _Alloc>::
00548       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
00549            std::forward_iterator_tag)
00550       {
00551     if (__beg == __end && __a == _Alloc())
00552       return _S_empty_rep._M_refcopy();
00553 
00554     // NB: Not required, but considered best practice.
00555     if (__is_null_pointer(__beg) && __beg != __end)
00556       std::__throw_logic_error(__N("__rc_string_base::"
00557                        "_S_construct NULL not valid"));
00558 
00559     const size_type __dnew = static_cast<size_type>(std::distance(__beg,
00560                                       __end));
00561     // Check for out_of_range and length_error exceptions.
00562     _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
00563     __try
00564       { _S_copy_chars(__r->_M_refdata(), __beg, __end); }
00565     __catch(...)
00566       {
00567         __r->_M_destroy(__a);
00568         __throw_exception_again;
00569       }
00570     __r->_M_set_length(__dnew);
00571     return __r->_M_refdata();
00572       }
00573 
00574   template<typename _CharT, typename _Traits, typename _Alloc>
00575     _CharT*
00576     __rc_string_base<_CharT, _Traits, _Alloc>::
00577     _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
00578     {
00579       if (__n == 0 && __a == _Alloc())
00580     return _S_empty_rep._M_refcopy();
00581 
00582       // Check for out_of_range and length_error exceptions.
00583       _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
00584       if (__n)
00585     _S_assign(__r->_M_refdata(), __n, __c);
00586 
00587       __r->_M_set_length(__n);
00588       return __r->_M_refdata();
00589     }
00590 
00591   template<typename _CharT, typename _Traits, typename _Alloc>
00592     void
00593     __rc_string_base<_CharT, _Traits, _Alloc>::
00594     _M_swap(__rc_string_base& __rcs)
00595     {
00596       if (_M_is_leaked())
00597     _M_set_sharable();
00598       if (__rcs._M_is_leaked())
00599     __rcs._M_set_sharable();
00600       
00601       _CharT* __tmp = _M_data();
00602       _M_data(__rcs._M_data());
00603       __rcs._M_data(__tmp);
00604 
00605       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00606       // 431. Swapping containers with unequal allocators.
00607       std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
00608                           __rcs._M_get_allocator());
00609     } 
00610 
00611   template<typename _CharT, typename _Traits, typename _Alloc>
00612     void
00613     __rc_string_base<_CharT, _Traits, _Alloc>::
00614     _M_assign(const __rc_string_base& __rcs)
00615     {
00616       if (_M_rep() != __rcs._M_rep())
00617     {
00618       _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
00619       _M_dispose();
00620       _M_data(__tmp);
00621     }
00622     }
00623 
00624   template<typename _CharT, typename _Traits, typename _Alloc>
00625     void
00626     __rc_string_base<_CharT, _Traits, _Alloc>::
00627     _M_reserve(size_type __res)
00628     {
00629       // Make sure we don't shrink below the current size.
00630       if (__res < _M_length())
00631     __res = _M_length();
00632       
00633       if (__res != _M_capacity() || _M_is_shared())
00634     {
00635       _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
00636                          __res - _M_length());
00637       _M_dispose();
00638       _M_data(__tmp);
00639     }
00640     }
00641 
00642   template<typename _CharT, typename _Traits, typename _Alloc>
00643     void
00644     __rc_string_base<_CharT, _Traits, _Alloc>::
00645     _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
00646           size_type __len2)
00647     {
00648       const size_type __how_much = _M_length() - __pos - __len1;
00649       
00650       _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
00651                   _M_capacity(), _M_get_allocator());
00652       
00653       if (__pos)
00654     _S_copy(__r->_M_refdata(), _M_data(), __pos);
00655       if (__s && __len2)
00656     _S_copy(__r->_M_refdata() + __pos, __s, __len2);
00657       if (__how_much)
00658     _S_copy(__r->_M_refdata() + __pos + __len2,
00659         _M_data() + __pos + __len1, __how_much);
00660       
00661       _M_dispose();
00662       _M_data(__r->_M_refdata());
00663     }
00664 
00665   template<typename _CharT, typename _Traits, typename _Alloc>
00666     void
00667     __rc_string_base<_CharT, _Traits, _Alloc>::
00668     _M_erase(size_type __pos, size_type __n)
00669     {
00670       const size_type __new_size = _M_length() - __n;
00671       const size_type __how_much = _M_length() - __pos - __n;
00672       
00673       if (_M_is_shared())
00674     {
00675       // Must reallocate.
00676       _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
00677                       _M_get_allocator());
00678 
00679       if (__pos)
00680         _S_copy(__r->_M_refdata(), _M_data(), __pos);
00681       if (__how_much)
00682         _S_copy(__r->_M_refdata() + __pos,
00683             _M_data() + __pos + __n, __how_much);
00684 
00685       _M_dispose();
00686       _M_data(__r->_M_refdata());
00687     }
00688       else if (__how_much && __n)
00689     {
00690       // Work in-place.
00691       _S_move(_M_data() + __pos,
00692           _M_data() + __pos + __n, __how_much);
00693     }
00694 
00695       _M_rep()->_M_set_length(__new_size);      
00696     }
00697 
00698   template<>
00699     inline bool
00700     __rc_string_base<char, std::char_traits<char>,
00701              std::allocator<char> >::
00702     _M_compare(const __rc_string_base& __rcs) const
00703     {
00704       if (_M_rep() == __rcs._M_rep())
00705     return true;
00706       return false;
00707     }
00708 
00709 #ifdef _GLIBCXX_USE_WCHAR_T
00710   template<>
00711     inline bool
00712     __rc_string_base<wchar_t, std::char_traits<wchar_t>,
00713              std::allocator<wchar_t> >::
00714     _M_compare(const __rc_string_base& __rcs) const
00715     {
00716       if (_M_rep() == __rcs._M_rep())
00717     return true;
00718       return false;
00719     }
00720 #endif
00721 
00722 _GLIBCXX_END_NAMESPACE
00723 
00724 #endif /* _RC_STRING_BASE_H */