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// Reference-counted versatile string base -*- C++ -*-

// Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010

// Free Software Foundation, Inc.

//

// This file is part of the GNU ISO C++ Library.  This library is free

// software; you can redistribute it and/or modify it under the

// terms of the GNU General Public License as published by the

// Free Software Foundation; either version 3, or (at your option)

// any later version.

// This library is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional

// permissions described in the GCC Runtime Library Exception, version

// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and

// a copy of the GCC Runtime Library Exception along with this program;

// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see

// <http://www.gnu.org/licenses/>.

/** @file ext/rc_string_base.h

 *  This file is a GNU extension to the Standard C++ Library.

 *  This is an internal header file, included by other library headers.

 *  You should not attempt to use it directly.

 */

#ifndef _RC_STRING_BASE_H

#define _RC_STRING_BASE_H 1

#include <ext/atomicity.h>

#include <bits/stl_iterator_base_funcs.h>

_GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)

  /**

   *  Documentation?  What's that?

   *  Nathan Myers <ncm@cantrip.org>.

   *

   *  A string looks like this:

   *

   *  @code

   *                                        [_Rep]

   *                                        _M_length

   *   [__rc_string_base<char_type>]        _M_capacity

   *   _M_dataplus                          _M_refcount

   *   _M_p ---------------->               unnamed array of char_type

   *  @endcode

   *

   *  Where the _M_p points to the first character in the string, and

   *  you cast it to a pointer-to-_Rep and subtract 1 to get a

   *  pointer to the header.

   *

   *  This approach has the enormous advantage that a string object

   *  requires only one allocation.  All the ugliness is confined

   *  within a single pair of inline functions, which each compile to

   *  a single @a add instruction: _Rep::_M_refdata(), and

   *  __rc_string_base::_M_rep(); and the allocation function which gets a

   *  block of raw bytes and with room enough and constructs a _Rep

   *  object at the front.

   *

   *  The reason you want _M_data pointing to the character array and

   *  not the _Rep is so that the debugger can see the string

   *  contents. (Probably we should add a non-inline member to get

   *  the _Rep for the debugger to use, so users can check the actual

   *  string length.)

   *

   *  Note that the _Rep object is a POD so that you can have a

   *  static <em>empty string</em> _Rep object already @a constructed before

   *  static constructors have run.  The reference-count encoding is

   *  chosen so that a 0 indicates one reference, so you never try to

   *  destroy the empty-string _Rep object.

   *

   *  All but the last paragraph is considered pretty conventional

   *  for a C++ string implementation.

  */

 template<typename _CharT, typename _Traits, typename _Alloc>

    class __rc_string_base

    : protected __vstring_utility<_CharT, _Traits, _Alloc>

    {

    public:

      typedef _Traits                                       traits_type;

      typedef typename _Traits::char_type                   value_type;

      typedef _Alloc                                        allocator_type;

      typedef __vstring_utility<_CharT, _Traits, _Alloc>    _Util_Base;

      typedef typename _Util_Base::_CharT_alloc_type        _CharT_alloc_type;

      typedef typename _CharT_alloc_type::size_type         size_type;

    private:

      // _Rep: string representation

      //   Invariants:

      //   1. String really contains _M_length + 1 characters: due to 21.3.4

      //      must be kept null-terminated.

      //   2. _M_capacity >= _M_length

      //      Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).

      //   3. _M_refcount has three states:

      //      -1: leaked, one reference, no ref-copies allowed, non-const.

      //       0: one reference, non-const.

      //     n>0: n + 1 references, operations require a lock, const.

      //   4. All fields == 0 is an empty string, given the extra storage

      //      beyond-the-end for a null terminator; thus, the shared

      //      empty string representation needs no constructor.

      struct _Rep

      {

        union

        {

          struct

          {

            size_type       _M_length;

            size_type       _M_capacity;

            _Atomic_word    _M_refcount;

          }                 _M_info;

          // Only for alignment purposes.

          _CharT            _M_align;

        };

        typedef typename _Alloc::template rebind<_Rep>::other _Rep_alloc_type;

        _CharT*

        _M_refdata() throw()

        { return reinterpret_cast<_CharT*>(this + 1); }

        _CharT*

        _M_refcopy() throw()

        {

          __atomic_add_dispatch(&_M_info._M_refcount, 1);

          return _M_refdata();

        }  // XXX MT

        void

        _M_set_length(size_type __n)

        {

          _M_info._M_refcount = 0;  // One reference.

          _M_info._M_length = __n;

          // grrr. (per 21.3.4)

          // You cannot leave those LWG people alone for a second.

          traits_type::assign(_M_refdata()[__n], _CharT());

        }

        // Create & Destroy

        static _Rep*

        _S_create(size_type, size_type, const _Alloc&);

        void

        _M_destroy(const _Alloc&) throw();

        _CharT*

        _M_clone(const _Alloc&, size_type __res = 0);

      };

      struct _Rep_empty

      : public _Rep

      {

        _CharT              _M_terminal;

      };

      static _Rep_empty     _S_empty_rep;

      // The maximum number of individual char_type elements of an

      // individual string is determined by _S_max_size. This is the

      // value that will be returned by max_size().  (Whereas npos

      // is the maximum number of bytes the allocator can allocate.)

      // If one was to divvy up the theoretical largest size string,

      // with a terminating character and m _CharT elements, it'd

      // look like this:

      // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)

      //        + sizeof(_Rep) - 1

      // (NB: last two terms for rounding reasons, see _M_create below)

      // Solving for m:

      // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1

      // In addition, this implementation halves this amount.

      enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)

                              + 1) / sizeof(_CharT)) - 1) / 2 };

      // Data Member (private):

      mutable typename _Util_Base::template _Alloc_hider<_Alloc>  _M_dataplus;

      void

      _M_data(_CharT* __p)

      { _M_dataplus._M_p = __p; }

      _Rep*

      _M_rep() const

      { return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }

      _CharT*

      _M_grab(const _Alloc& __alloc) const

      {

        return (!_M_is_leaked() && _M_get_allocator() == __alloc)

                ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);

      }

      void

      _M_dispose()

      {

        if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,

                                        -1) <= 0)

          _M_rep()->_M_destroy(_M_get_allocator());

      }  // XXX MT

      bool

      _M_is_leaked() const

      { return _M_rep()->_M_info._M_refcount < 0; }

      void

      _M_set_sharable()

      { _M_rep()->_M_info._M_refcount = 0; }

      void

      _M_leak_hard();

      // _S_construct_aux is used to implement the 21.3.1 para 15 which

      // requires special behaviour if _InIterator is an integral type

      template<typename _InIterator>

        static _CharT*

        _S_construct_aux(_InIterator __beg, _InIterator __end,

                         const _Alloc& __a, std::__false_type)

        {

          typedef typename iterator_traits<_InIterator>::iterator_category _Tag;

          return _S_construct(__beg, __end, __a, _Tag());

        }

      // _GLIBCXX_RESOLVE_LIB_DEFECTS

      // 438. Ambiguity in the "do the right thing" clause

      template<typename _Integer>

        static _CharT*

        _S_construct_aux(_Integer __beg, _Integer __end,

                         const _Alloc& __a, std::__true_type)

        { return _S_construct_aux_2(static_cast<size_type>(__beg),

                                    __end, __a); }

      static _CharT*

      _S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)

      { return _S_construct(__req, __c, __a); }

      template<typename _InIterator>

        static _CharT*

        _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)

        {

          typedef typename std::__is_integer<_InIterator>::__type _Integral;

          return _S_construct_aux(__beg, __end, __a, _Integral());

        }

      // For Input Iterators, used in istreambuf_iterators, etc.

      template<typename _InIterator>

        static _CharT*

         _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,

                      std::input_iterator_tag);

      // For forward_iterators up to random_access_iterators, used for

      // string::iterator, _CharT*, etc.

      template<typename _FwdIterator>

        static _CharT*

        _S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,

                     std::forward_iterator_tag);

      static _CharT*

      _S_construct(size_type __req, _CharT __c, const _Alloc& __a);

    public:

      size_type

      _M_max_size() const

      { return size_type(_S_max_size); }

      _CharT*

      _M_data() const

      { return _M_dataplus._M_p; }

      size_type

      _M_length() const

      { return _M_rep()->_M_info._M_length; }

      size_type

      _M_capacity() const

      { return _M_rep()->_M_info._M_capacity; }

      bool

      _M_is_shared() const

      { return _M_rep()->_M_info._M_refcount > 0; }

      void

      _M_set_leaked()

      { _M_rep()->_M_info._M_refcount = -1; }

      void

      _M_leak()    // for use in begin() & non-const op[]

      {

        if (!_M_is_leaked())

          _M_leak_hard();

      }

      void

      _M_set_length(size_type __n)

      { _M_rep()->_M_set_length(__n); }

      __rc_string_base()

      : _M_dataplus(_S_empty_rep._M_refcopy()) { }

      __rc_string_base(const _Alloc& __a);

      __rc_string_base(const __rc_string_base& __rcs);

#ifdef __GXX_EXPERIMENTAL_CXX0X__

      __rc_string_base(__rc_string_base&& __rcs)

      : _M_dataplus(__rcs._M_dataplus)

      { __rcs._M_data(_S_empty_rep._M_refcopy()); }

#endif

      __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);

      template<typename _InputIterator>

        __rc_string_base(_InputIterator __beg, _InputIterator __end,

                         const _Alloc& __a);

      ~__rc_string_base()

      { _M_dispose(); }

      allocator_type&

      _M_get_allocator()

      { return _M_dataplus; }

      const allocator_type&

      _M_get_allocator() const

      { return _M_dataplus; }

      void

      _M_swap(__rc_string_base& __rcs);

      void

      _M_assign(const __rc_string_base& __rcs);

      void

      _M_reserve(size_type __res);

      void

      _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,

                size_type __len2);

      void

      _M_erase(size_type __pos, size_type __n);

      void

      _M_clear()

      { _M_erase(size_type(0), _M_length()); }

      bool

      _M_compare(const __rc_string_base&) const

      { return false; }

    };

  template<typename _CharT, typename _Traits, typename _Alloc>

    typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep_empty

    __rc_string_base<_CharT, _Traits, _Alloc>::_S_empty_rep;

  template<typename _CharT, typename _Traits, typename _Alloc>

    typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep*

    __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::

    _S_create(size_type __capacity, size_type __old_capacity,

              const _Alloc& __alloc)

    {

      // _GLIBCXX_RESOLVE_LIB_DEFECTS

      // 83.  String::npos vs. string::max_size()

      if (__capacity > size_type(_S_max_size))

        std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));

      // The standard places no restriction on allocating more memory

      // than is strictly needed within this layer at the moment or as

      // requested by an explicit application call to reserve().

      // Many malloc implementations perform quite poorly when an

      // application attempts to allocate memory in a stepwise fashion

      // growing each allocation size by only 1 char.  Additionally,

      // it makes little sense to allocate less linear memory than the

      // natural blocking size of the malloc implementation.

      // Unfortunately, we would need a somewhat low-level calculation

      // with tuned parameters to get this perfect for any particular

      // malloc implementation.  Fortunately, generalizations about

      // common features seen among implementations seems to suffice.

      // __pagesize need not match the actual VM page size for good

      // results in practice, thus we pick a common value on the low

      // side.  __malloc_header_size is an estimate of the amount of

      // overhead per memory allocation (in practice seen N * sizeof

      // (void*) where N is 0, 2 or 4).  According to folklore,

      // picking this value on the high side is better than

      // low-balling it (especially when this algorithm is used with

      // malloc implementations that allocate memory blocks rounded up

      // to a size which is a power of 2).

      const size_type __pagesize = 4096;

      const size_type __malloc_header_size = 4 * sizeof(void*);

      // The below implements an exponential growth policy, necessary to

      // meet amortized linear time requirements of the library: see

      // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.

      if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)

        {

          __capacity = 2 * __old_capacity;

          // Never allocate a string bigger than _S_max_size.

          if (__capacity > size_type(_S_max_size))

            __capacity = size_type(_S_max_size);

        }

      // NB: Need an array of char_type[__capacity], plus a terminating

      // null char_type() element, plus enough for the _Rep data structure,

      // plus sizeof(_Rep) - 1 to upper round to a size multiple of

      // sizeof(_Rep).

      // Whew. Seemingly so needy, yet so elemental.

      size_type __size = ((__capacity + 1) * sizeof(_CharT)

                          + 2 * sizeof(_Rep) - 1);

      const size_type __adj_size = __size + __malloc_header_size;

      if (__adj_size > __pagesize && __capacity > __old_capacity)

        {

          const size_type __extra = __pagesize - __adj_size % __pagesize;

          __capacity += __extra / sizeof(_CharT);

          if (__capacity > size_type(_S_max_size))

            __capacity = size_type(_S_max_size);

          __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;

        }

      // NB: Might throw, but no worries about a leak, mate: _Rep()

      // does not throw.

      _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));

      _Rep* __p = new (__place) _Rep;

      __p->_M_info._M_capacity = __capacity;

      return __p;

    }

  template<typename _CharT, typename _Traits, typename _Alloc>

    void

    __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::

    _M_destroy(const _Alloc& __a) throw ()

    {

      const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)

                                + 2 * sizeof(_Rep) - 1);

      _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));

    }

  template<typename _CharT, typename _Traits, typename _Alloc>

    _CharT*

    __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::

    _M_clone(const _Alloc& __alloc, size_type __res)

    {

      // Requested capacity of the clone.

      const size_type __requested_cap = _M_info._M_length + __res;

      _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,

                                  __alloc);

      if (_M_info._M_length)

        _S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);

      __r->_M_set_length(_M_info._M_length);

      return __r->_M_refdata();

    }

  template<typename _CharT, typename _Traits, typename _Alloc>

    __rc_string_base<_CharT, _Traits, _Alloc>::

    __rc_string_base(const _Alloc& __a)

    : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }

  template<typename _CharT, typename _Traits, typename _Alloc>

    __rc_string_base<_CharT, _Traits, _Alloc>::

    __rc_string_base(const __rc_string_base& __rcs)

    : _M_dataplus(__rcs._M_get_allocator(),

                  __rcs._M_grab(__rcs._M_get_allocator())) { }

  template<typename _CharT, typename _Traits, typename _Alloc>

    __rc_string_base<_CharT, _Traits, _Alloc>::

    __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)

    : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }

  template<typename _CharT, typename _Traits, typename _Alloc>

    template<typename _InputIterator>

    __rc_string_base<_CharT, _Traits, _Alloc>::

    __rc_string_base(_InputIterator __beg, _InputIterator __end,

                     const _Alloc& __a)

    : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }

  template<typename _CharT, typename _Traits, typename _Alloc>

    void

    __rc_string_base<_CharT, _Traits, _Alloc>::

    _M_leak_hard()

    {

      if (_M_is_shared())

        _M_erase(0, 0);

      _M_set_leaked();

    }

  // NB: This is the special case for Input Iterators, used in

  // istreambuf_iterators, etc.

  // Input Iterators have a cost structure very different from

  // pointers, calling for a different coding style.

  template<typename _CharT, typename _Traits, typename _Alloc>

    template<typename _InIterator>

      _CharT*

      __rc_string_base<_CharT, _Traits, _Alloc>::

      _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,

                   std::input_iterator_tag)

      {

        if (__beg == __end && __a == _Alloc())

          return _S_empty_rep._M_refcopy();

        // Avoid reallocation for common case.

        _CharT __buf[128];

        size_type __len = 0;

        while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))

          {

            __buf[__len++] = *__beg;

            ++__beg;

          }

        _Rep* __r = _Rep::_S_create(__len, size_type(0), __a);

        _S_copy(__r->_M_refdata(), __buf, __len);

        __try

          {

            while (__beg != __end)

              {

                if (__len == __r->_M_info._M_capacity)

                  {

                    // Allocate more space.

                    _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);

                    _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);

                    __r->_M_destroy(__a);

                    __r = __another;

                  }

                __r->_M_refdata()[__len++] = *__beg;

                ++__beg;

              }

          }

        __catch(...)

          {

            __r->_M_destroy(__a);

            __throw_exception_again;

          }

        __r->_M_set_length(__len);

        return __r->_M_refdata();

      }

  template<typename _CharT, typename _Traits, typename _Alloc>

    template<typename _InIterator>

      _CharT*

      __rc_string_base<_CharT, _Traits, _Alloc>::

      _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,

                   std::forward_iterator_tag)

      {

        if (__beg == __end && __a == _Alloc())

          return _S_empty_rep._M_refcopy();

        // NB: Not required, but considered best practice.

        if (__is_null_pointer(__beg) && __beg != __end)

          std::__throw_logic_error(__N("__rc_string_base::"

                                       "_S_construct NULL not valid"));

        const size_type __dnew = static_cast<size_type>(std::distance(__beg,

                                                                      __end));

        // Check for out_of_range and length_error exceptions.

        _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);

        __try

          { _S_copy_chars(__r->_M_refdata(), __beg, __end); }

        __catch(...)

          {

            __r->_M_destroy(__a);

            __throw_exception_again;

          }

        __r->_M_set_length(__dnew);

        return __r->_M_refdata();

      }

  template<typename _CharT, typename _Traits, typename _Alloc>

    _CharT*

    __rc_string_base<_CharT, _Traits, _Alloc>::

    _S_construct(size_type __n, _CharT __c, const _Alloc& __a)

    {

      if (__n == 0 && __a == _Alloc())

        return _S_empty_rep._M_refcopy();

      // Check for out_of_range and length_error exceptions.

      _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);

      if (__n)

        _S_assign(__r->_M_refdata(), __n, __c);

      __r->_M_set_length(__n);

      return __r->_M_refdata();

    }

  template<typename _CharT, typename _Traits, typename _Alloc>

    void

    __rc_string_base<_CharT, _Traits, _Alloc>::

    _M_swap(__rc_string_base& __rcs)

    {

      if (_M_is_leaked())

        _M_set_sharable();

      if (__rcs._M_is_leaked())

        __rcs._M_set_sharable();

      _CharT* __tmp = _M_data();

      _M_data(__rcs._M_data());

      __rcs._M_data(__tmp);

      // _GLIBCXX_RESOLVE_LIB_DEFECTS

      // 431. Swapping containers with unequal allocators.

      std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),

                                                  __rcs._M_get_allocator());

    }

  template<typename _CharT, typename _Traits, typename _Alloc>

    void

    __rc_string_base<_CharT, _Traits, _Alloc>::

    _M_assign(const __rc_string_base& __rcs)

    {

      if (_M_rep() != __rcs._M_rep())

        {

          _CharT* __tmp = __rcs._M_grab(_M_get_allocator());

          _M_dispose();

          _M_data(__tmp);

        }

    }

  template<typename _CharT, typename _Traits, typename _Alloc>

    void

    __rc_string_base<_CharT, _Traits, _Alloc>::

    _M_reserve(size_type __res)

    {

      // Make sure we don't shrink below the current size.

      if (__res < _M_length())

        __res = _M_length();

      if (__res != _M_capacity() || _M_is_shared())

        {

          _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),

                                             __res - _M_length());

          _M_dispose();

          _M_data(__tmp);

        }

    }

  template<typename _CharT, typename _Traits, typename _Alloc>

    void

    __rc_string_base<_CharT, _Traits, _Alloc>::

    _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,

              size_type __len2)

    {

      const size_type __how_much = _M_length() - __pos - __len1;

      _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,

                                  _M_capacity(), _M_get_allocator());

      if (__pos)

        _S_copy(__r->_M_refdata(), _M_data(), __pos);

      if (__s && __len2)

        _S_copy(__r->_M_refdata() + __pos, __s, __len2);

      if (__how_much)

        _S_copy(__r->_M_refdata() + __pos + __len2,

                _M_data() + __pos + __len1, __how_much);

      _M_dispose();

      _M_data(__r->_M_refdata());

    }

  template<typename _CharT, typename _Traits, typename _Alloc>

    void

    __rc_string_base<_CharT, _Traits, _Alloc>::

    _M_erase(size_type __pos, size_type __n)

    {

      const size_type __new_size = _M_length() - __n;

      const size_type __how_much = _M_length() - __pos - __n;

      if (_M_is_shared())

        {

          // Must reallocate.

          _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),

                                      _M_get_allocator());

          if (__pos)

            _S_copy(__r->_M_refdata(), _M_data(), __pos);

          if (__how_much)

            _S_copy(__r->_M_refdata() + __pos,

                    _M_data() + __pos + __n, __how_much);