rc_string_base.h

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

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