gcc/libstdc++-v3/include/bits/stl_deque.h

// Deque implementation -*- C++ -*-

// Copyright (C) 2001, 2002 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 2, 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.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

/*
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1997
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */

/** @file stl_deque.h
 *  This is an internal header file, included by other library headers.
 *  You should not attempt to use it directly.
 */

#ifndef __GLIBCPP_INTERNAL_DEQUE_H
#define __GLIBCPP_INTERNAL_DEQUE_H

#include <bits/concept_check.h>
#include <bits/stl_iterator_base_types.h>
#include <bits/stl_iterator_base_funcs.h>

// Since this entire file is within namespace std, there's no reason to
// waste two spaces along the left column.  Thus the leading indentation is
// slightly violated from here on.
namespace std
{ 

/**
 *  @if maint
 *  @brief This function controls the size of memory nodes.
 *  @param  size  The size of an element.
 *  @return   The number (not byte size) of elements per node.
 *
 *  This function started off as a compiler kludge from SGI, but seems to
 *  be a useful wrapper around a repeated constant expression.  The '512' is
 *  tuneable (and no other code needs to change), but no investigation has
 *  been done since inheriting the SGI code.
 *  @endif
*/
inline size_t 
__deque_buf_size(size_t __size) 
  { return __size < 512 ? size_t(512 / __size) : size_t(1); }


/**
 *  @brief A deque::iterator.
 *
 *  Quite a bit of intelligence here.  Much of the functionality of deque is
 *  actually passed off to this class.  A deque holds two of these internally,
 *  marking its valid range.  Access to elements is done as offsets of either
 *  of those two, relying on operator overloading in this class.
 *
 *  @if maint
 *  All the functions are op overloads except for _M_set_node.
 *  @endif
*/
template <typename _Tp, typename _Ref, typename _Ptr>
  struct _Deque_iterator
{
  typedef _Deque_iterator<_Tp, _Tp&, _Tp*>             iterator;
  typedef _Deque_iterator<_Tp, const _Tp&, const _Tp*> const_iterator;
  static size_t _S_buffer_size() { return __deque_buf_size(sizeof(_Tp)); }

  typedef random_access_iterator_tag iterator_category;
  typedef _Tp                        value_type;
  typedef _Ptr                       pointer;
  typedef _Ref                       reference;
  typedef size_t                     size_type;
  typedef ptrdiff_t                  difference_type;
  typedef _Tp**                      _Map_pointer;
  typedef _Deque_iterator            _Self;

  _Tp* _M_cur;
  _Tp* _M_first;
  _Tp* _M_last;
  _Map_pointer _M_node;

  _Deque_iterator(_Tp* __x, _Map_pointer __y) 
    : _M_cur(__x), _M_first(*__y),
      _M_last(*__y + _S_buffer_size()), _M_node(__y) {}
  _Deque_iterator() : _M_cur(0), _M_first(0), _M_last(0), _M_node(0) {}
  _Deque_iterator(const iterator& __x)
    : _M_cur(__x._M_cur), _M_first(__x._M_first), 
      _M_last(__x._M_last), _M_node(__x._M_node) {}

  reference operator*() const { return *_M_cur; }
  pointer operator->() const { return _M_cur; }

  _Self& operator++() {
    ++_M_cur;
    if (_M_cur == _M_last) {
      _M_set_node(_M_node + 1);
      _M_cur = _M_first;
    }
    return *this; 
  }
  _Self operator++(int)  {
    _Self __tmp = *this;
    ++*this;
    return __tmp;
  }

  _Self& operator--() {
    if (_M_cur == _M_first) {
      _M_set_node(_M_node - 1);
      _M_cur = _M_last;
    }
    --_M_cur;
    return *this;
  }
  _Self operator--(int) {
    _Self __tmp = *this;
    --*this;
    return __tmp;
  }

  _Self& operator+=(difference_type __n)
  {
    difference_type __offset = __n + (_M_cur - _M_first);
    if (__offset >= 0 && __offset < difference_type(_S_buffer_size()))
      _M_cur += __n;
    else {
      difference_type __node_offset =
        __offset > 0 ? __offset / difference_type(_S_buffer_size())
                   : -difference_type((-__offset - 1) / _S_buffer_size()) - 1;
      _M_set_node(_M_node + __node_offset);
      _M_cur = _M_first + 
        (__offset - __node_offset * difference_type(_S_buffer_size()));
    }
    return *this;
  }

  _Self operator+(difference_type __n) const
  {
    _Self __tmp = *this;
    return __tmp += __n;
  }

  _Self& operator-=(difference_type __n) { return *this += -__n; }
 
  _Self operator-(difference_type __n) const {
    _Self __tmp = *this;
    return __tmp -= __n;
  }

  reference operator[](difference_type __n) const { return *(*this + __n); }

  /** @if maint
   *  Prepares to traverse new_node.  Sets everything except _M_cur, which
   *  should therefore be set by the caller immediately afterwards, based on
   *  _M_first and _M_last.
   *  @endif
  */
  void
  _M_set_node(_Map_pointer __new_node)
  {
    _M_node = __new_node;
    _M_first = *__new_node;
    _M_last = _M_first + difference_type(_S_buffer_size());
  }
};

// Note: we also provide overloads whose operands are of the same type in
// order to avoid ambiguous overload resolution when std::rel_ops operators
// are in scope (for additional details, see libstdc++/3628)
template <typename _Tp, typename _Ref, typename _Ptr>
inline bool
operator==(const _Deque_iterator<_Tp, _Ref, _Ptr>& __x,
	   const _Deque_iterator<_Tp, _Ref, _Ptr>& __y)
{
  return __x._M_cur == __y._M_cur;
}

template <typename _Tp, typename _RefL, typename _PtrL,
                        typename _RefR, typename _PtrR>
inline bool
operator==(const _Deque_iterator<_Tp, _RefL, _PtrL>& __x,
	   const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
{
  return __x._M_cur == __y._M_cur;
}

template <typename _Tp, typename _Ref, typename _Ptr>
inline bool
operator!=(const _Deque_iterator<_Tp, _Ref, _Ptr>& __x,
	   const _Deque_iterator<_Tp, _Ref, _Ptr>& __y)
{
  return !(__x == __y);
}

template <typename _Tp, typename _RefL, typename _PtrL,
                        typename _RefR, typename _PtrR>
inline bool
operator!=(const _Deque_iterator<_Tp, _RefL, _PtrL>& __x,
	   const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
{
  return !(__x == __y);
}

template <typename _Tp, typename _Ref, typename _Ptr>
inline bool
operator<(const _Deque_iterator<_Tp, _Ref, _Ptr>& __x,
	   const _Deque_iterator<_Tp, _Ref, _Ptr>& __y)
{
  return (__x._M_node == __y._M_node) ? 
    (__x._M_cur < __y._M_cur) : (__x._M_node < __y._M_node);
}

template <typename _Tp, typename _RefL, typename _PtrL,
                        typename _RefR, typename _PtrR>
inline bool
operator<(const _Deque_iterator<_Tp, _RefL, _PtrL>& __x,
	   const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
{
  return (__x._M_node == __y._M_node) ? 
    (__x._M_cur < __y._M_cur) : (__x._M_node < __y._M_node);
}

template <typename _Tp, typename _Ref, typename _Ptr>
inline bool
operator>(const _Deque_iterator<_Tp, _Ref, _Ptr>& __x,
	   const _Deque_iterator<_Tp, _Ref, _Ptr>& __y)
{
  return __y < __x;
}

template <typename _Tp, typename _RefL, typename _PtrL,
                        typename _RefR, typename _PtrR>
inline bool
operator>(const _Deque_iterator<_Tp, _RefL, _PtrL>& __x,
	   const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
{
  return __y < __x;
}

template <typename _Tp, typename _Ref, typename _Ptr>
inline bool
operator<=(const _Deque_iterator<_Tp, _Ref, _Ptr>& __x,
	   const _Deque_iterator<_Tp, _Ref, _Ptr>& __y)
{
  return !(__y < __x);
}

template <typename _Tp, typename _RefL, typename _PtrL,
                        typename _RefR, typename _PtrR>
inline bool
operator<=(const _Deque_iterator<_Tp, _RefL, _PtrL>& __x,
	   const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
{
  return !(__y < __x);
}

template <typename _Tp, typename _Ref, typename _Ptr>
inline bool
operator>=(const _Deque_iterator<_Tp, _Ref, _Ptr>& __x,
	   const _Deque_iterator<_Tp, _Ref, _Ptr>& __y)
{
  return !(__x < __y);
}

template <typename _Tp, typename _RefL, typename _PtrL,
                        typename _RefR, typename _PtrR>
inline bool
operator>=(const _Deque_iterator<_Tp, _RefL, _PtrL>& __x,
	   const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
{
  return !(__x < __y);
}

// _GLIBCPP_RESOLVE_LIB_DEFECTS
// According to the resolution of DR179 not only the various comparison
// operators but also operator- must accept mixed iterator/const_iterator
// parameters.
template <typename _Tp, typename _RefL, typename _PtrL,
                        typename _RefR, typename _PtrR>
inline typename _Deque_iterator<_Tp, _RefL, _PtrL>::difference_type
operator-(const _Deque_iterator<_Tp, _RefL, _PtrL>& __x,
	  const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
{
  return _Deque_iterator<_Tp, _RefL, _PtrL>::difference_type
    (_Deque_iterator<_Tp, _RefL, _PtrL>::_S_buffer_size()) *
    (__x._M_node - __y._M_node - 1) + (__x._M_cur - __x._M_first) +
    (__y._M_last - __y._M_cur);
}

template <typename _Tp, typename _Ref, typename _Ptr>
inline _Deque_iterator<_Tp, _Ref, _Ptr>
operator+(ptrdiff_t __n, const _Deque_iterator<_Tp, _Ref, _Ptr>& __x)
{
  return __x + __n;
}


/// @if maint Primary default version.  @endif
/**
 *  @if maint
 *  Deque base class.  It has two purposes.  First, its constructor
 *  and destructor allocate (but don't initialize) storage.  This makes
 *  %exception safety easier.  Second, the base class encapsulates all of
 *  the differences between SGI-style allocators and standard-conforming
 *  allocators.  (See stl_alloc.h for more on this topic.)  There are two
 *  versions:  this ordinary one, and the space-saving specialization for
 *  instanceless allocators.
 *  @endif
*/
template <typename _Tp, typename _Alloc, bool __is_static>
  class _Deque_alloc_base
{
public:
  typedef typename _Alloc_traits<_Tp,_Alloc>::allocator_type allocator_type;
  allocator_type get_allocator() const { return _M_node_allocator; }

  _Deque_alloc_base(const allocator_type& __a)
    : _M_node_allocator(__a), _M_map_allocator(__a),
      _M_map(0), _M_map_size(0)
  {}
  
protected:
  typedef typename _Alloc_traits<_Tp*, _Alloc>::allocator_type
          _Map_allocator_type;

  _Tp*
  _M_allocate_node()
  {
    return _M_node_allocator.allocate(__deque_buf_size(sizeof(_Tp)));
  }

  void
  _M_deallocate_node(_Tp* __p)
  {
    _M_node_allocator.deallocate(__p, __deque_buf_size(sizeof(_Tp)));
  }

  _Tp**
  _M_allocate_map(size_t __n) 
    { return _M_map_allocator.allocate(__n); }

  void
  _M_deallocate_map(_Tp** __p, size_t __n) 
    { _M_map_allocator.deallocate(__p, __n); }

  allocator_type       _M_node_allocator;
  _Map_allocator_type  _M_map_allocator;
  _Tp**                _M_map;
  size_t               _M_map_size;
};

/// @if maint Specialization for instanceless allocators.  @endif
template <typename _Tp, typename _Alloc>
  class _Deque_alloc_base<_Tp, _Alloc, true>
{
public:
  typedef typename _Alloc_traits<_Tp,_Alloc>::allocator_type allocator_type;
  allocator_type get_allocator() const { return allocator_type(); }

  _Deque_alloc_base(const allocator_type&)
    : _M_map(0), _M_map_size(0)
  {}
  
protected:
  typedef typename _Alloc_traits<_Tp,_Alloc>::_Alloc_type  _Node_alloc_type;
  typedef typename _Alloc_traits<_Tp*,_Alloc>::_Alloc_type _Map_alloc_type;

  _Tp*
  _M_allocate_node()
  {
    return _Node_alloc_type::allocate(__deque_buf_size(sizeof(_Tp)));
  }

  void
  _M_deallocate_node(_Tp* __p)
  {
    _Node_alloc_type::deallocate(__p, __deque_buf_size(sizeof(_Tp)));
  }

  _Tp**
  _M_allocate_map(size_t __n) 
    { return _Map_alloc_type::allocate(__n); }

  void
  _M_deallocate_map(_Tp** __p, size_t __n) 
    { _Map_alloc_type::deallocate(__p, __n); }

  _Tp**   _M_map;
  size_t  _M_map_size;
};


/**
 *  @if maint
 *  Deque base class.  Using _Alloc_traits in the instantiation of the parent
 *  class provides the compile-time dispatching mentioned in the parent's docs.
 *  This class provides the unified face for %deque's allocation.
 *
 *  Nothing in this class ever constructs or destroys an actual Tp element.
 *  (Deque handles that itself.)  Only/All memory management is performed here.
 *  @endif
*/
template <typename _Tp, typename _Alloc>
  class _Deque_base
  : public _Deque_alloc_base<_Tp,_Alloc,
                              _Alloc_traits<_Tp, _Alloc>::_S_instanceless>
{
public:
  typedef _Deque_alloc_base<_Tp,_Alloc,
                             _Alloc_traits<_Tp, _Alloc>::_S_instanceless>
          _Base;
  typedef typename _Base::allocator_type             allocator_type;
  typedef _Deque_iterator<_Tp,_Tp&,_Tp*>             iterator;
  typedef _Deque_iterator<_Tp,const _Tp&,const _Tp*> const_iterator;

  _Deque_base(const allocator_type& __a, size_t __num_elements)
    : _Base(__a), _M_start(), _M_finish()
    { _M_initialize_map(__num_elements); }
  _Deque_base(const allocator_type& __a) 
    : _Base(__a), _M_start(), _M_finish() {}
  ~_Deque_base();    

protected:
  void _M_initialize_map(size_t);
  void _M_create_nodes(_Tp** __nstart, _Tp** __nfinish);
  void _M_destroy_nodes(_Tp** __nstart, _Tp** __nfinish);
  enum { _S_initial_map_size = 8 };

  iterator _M_start;
  iterator _M_finish;
};


template <typename _Tp, typename _Alloc>
_Deque_base<_Tp,_Alloc>::~_Deque_base()
{
  if (_M_map)
  {
    _M_destroy_nodes(_M_start._M_node, _M_finish._M_node + 1);
    _M_deallocate_map(_M_map, _M_map_size);
  }
}

/**
 *  @if maint
 *  @brief Layout storage.
 *  @param  num_elements  The count of T's for which to allocate space at first.
 *  @return   Nothing.
 *
 *  The initial underlying memory layout is a bit complicated...
 *  @endif
*/
template <typename _Tp, typename _Alloc>
void
_Deque_base<_Tp,_Alloc>::_M_initialize_map(size_t __num_elements)
{
  size_t __num_nodes = 
    __num_elements / __deque_buf_size(sizeof(_Tp)) + 1;

  _M_map_size = max((size_t) _S_initial_map_size, __num_nodes + 2);
  _M_map = _M_allocate_map(_M_map_size);

  // For "small" maps (needing less than _M_map_size nodes), allocation
  // starts in the middle elements and grows outwards.  So nstart may be the
  // beginning of _M_map, but for small maps it may be as far in as _M_map+3.

  _Tp** __nstart = _M_map + (_M_map_size - __num_nodes) / 2;
  _Tp** __nfinish = __nstart + __num_nodes;
    
  try 
    { _M_create_nodes(__nstart, __nfinish); }
  catch(...)
    {
      _M_deallocate_map(_M_map, _M_map_size);
      _M_map = 0;
      _M_map_size = 0;
      __throw_exception_again;
    }
  
  _M_start._M_set_node(__nstart);
  _M_finish._M_set_node(__nfinish - 1);
  _M_start._M_cur = _M_start._M_first;
  _M_finish._M_cur = _M_finish._M_first +
                     __num_elements % __deque_buf_size(sizeof(_Tp));
}

template <typename _Tp, typename _Alloc>
void _Deque_base<_Tp,_Alloc>::_M_create_nodes(_Tp** __nstart, _Tp** __nfinish)
{
  _Tp** __cur;
  try
    {
      for (__cur = __nstart; __cur < __nfinish; ++__cur)
        *__cur = _M_allocate_node();
    }
  catch(...)
    { 
      _M_destroy_nodes(__nstart, __cur);
      __throw_exception_again; 
    }
}

template <typename _Tp, typename _Alloc>
void
_Deque_base<_Tp,_Alloc>::_M_destroy_nodes(_Tp** __nstart, _Tp** __nfinish)
{
  for (_Tp** __n = __nstart; __n < __nfinish; ++__n)
    _M_deallocate_node(*__n);
}


/**
 *  @brief  A standard container using fixed-size memory allocation and
 *  constant-time manipulation of elements at either end.
 *
 *  @ingroup Containers
 *  @ingroup Sequences
 *
 *  Meets the requirements of a <a href="tables.html#65">container</a>, a
 *  <a href="tables.html#66">reversible container</a>, and a
 *  <a href="tables.html#67">sequence</a>, including the
 *  <a href="tables.html#68">optional sequence requirements</a>.
 *
 *  In previous HP/SGI versions of deque, there was an extra template parameter
 *  so users could control the node size.  This extension turned out to violate
 *  the C++ standard (it can be detected using template template parameters),
 *  and it was removed.
 *
 *  @if maint
 *  Here's how a deque<Tp> manages memory.  Each deque has 4 members:
 *  
 *  - Tp**        _M_map
 *  - size_t      _M_map_size
 *  - iterator    _M_start, _M_finish
 *  
 *  map_size is at least 8.  %map is an array of map_size pointers-to-"nodes".
 *  (The name %map has nothing to do with the std::map class, and "nodes"
 *  should not be confused with std::list's usage of "node".)
 *  
 *  A "node" has no specific type name as such, but it is referred to as
 *  "node" in this file.  It is a simple array-of-Tp.  If Tp is very large,
 *  there will be one Tp element per node (i.e., an "array" of one).
 *  For non-huge Tp's, node size is inversely related to Tp size:  the
 *  larger the Tp, the fewer Tp's will fit in a node.  The goal here is to
 *  keep the total size of a node relatively small and constant over different
 *  Tp's, to improve allocator efficiency.
 *  
 *  **** As I write this, the nodes are /not/ allocated using the high-speed
 *  memory pool.  There are 20 hours left in the year; perhaps I can fix
 *  this before 2002.
 *  
 *  Not every pointer in the %map array will point to a node.  If the initial
 *  number of elements in the deque is small, the /middle/ %map pointers will
 *  be valid, and the ones at the edges will be unused.  This same situation
 *  will arise as the %map grows:  available %map pointers, if any, will be on
 *  the ends.  As new nodes are created, only a subset of the %map's pointers
 *  need to be copied "outward".
 *
 *  Class invariants:
 * - For any nonsingular iterator i:
 *    - i.node points to a member of the %map array.  (Yes, you read that
 *      correctly:  i.node does not actually point to a node.)  The member of
 *      the %map array is what actually points to the node.
 *    - i.first == *(i.node)    (This points to the node (first Tp element).)
 *    - i.last  == i.first + node_size
 *    - i.cur is a pointer in the range [i.first, i.last).  NOTE:
 *      the implication of this is that i.cur is always a dereferenceable
 *      pointer, even if i is a past-the-end iterator.
 * - Start and Finish are always nonsingular iterators.  NOTE: this means that
 *   an empty deque must have one node, a deque with <N elements (where N is
 *   the node buffer size) must have one node, a deque with N through (2N-1)
 *   elements must have two nodes, etc.
 * - For every node other than start.node and finish.node, every element in the
 *   node is an initialized object.  If start.node == finish.node, then
 *   [start.cur, finish.cur) are initialized objects, and the elements outside
 *   that range are uninitialized storage.  Otherwise, [start.cur, start.last)
 *   and [finish.first, finish.cur) are initialized objects, and [start.first,
 *   start.cur) and [finish.cur, finish.last) are uninitialized storage.
 * - [%map, %map + map_size) is a valid, non-empty range.  
 * - [start.node, finish.node] is a valid range contained within 
 *   [%map, %map + map_size).  
 * - A pointer in the range [%map, %map + map_size) points to an allocated node
 *   if and only if the pointer is in the range [start.node, finish.node].
 *
 *  Here's the magic:  nothing in deque is "aware" of the discontiguous storage!
 *
 *  The memory setup and layout occurs in the parent, _Base, and the iterator
 *  class is entirely responsible for "leaping" from one node to the next.  All
 *  the implementation routines for deque itself work only through the start
 *  and finish iterators.  This keeps the routines simple and sane, and we can
 *  use other standard algorithms as well.
 *  @endif
*/
template <typename _Tp, typename _Alloc = allocator<_Tp> >
  class deque : protected _Deque_base<_Tp, _Alloc>
{
  // concept requirements
  __glibcpp_class_requires(_Tp, _SGIAssignableConcept)

  typedef _Deque_base<_Tp, _Alloc>           _Base;

public:
  typedef _Tp                                value_type;
  typedef value_type*                        pointer;
  typedef const value_type*                  const_pointer;
  typedef typename _Base::iterator           iterator;
  typedef typename _Base::const_iterator     const_iterator;
  typedef reverse_iterator<const_iterator>   const_reverse_iterator;
  typedef reverse_iterator<iterator>         reverse_iterator;
  typedef value_type&                        reference;
  typedef const value_type&                  const_reference;
  typedef size_t                             size_type;
  typedef ptrdiff_t                          difference_type;
  typedef typename _Base::allocator_type     allocator_type;

protected:
  typedef pointer*                           _Map_pointer;
  static size_t _S_buffer_size() { return __deque_buf_size(sizeof(_Tp)); }

  // Functions controlling memory layout, and nothing else.
  using _Base::_M_initialize_map;
  using _Base::_M_create_nodes;
  using _Base::_M_destroy_nodes;
  using _Base::_M_allocate_node;
  using _Base::_M_deallocate_node;
  using _Base::_M_allocate_map;
  using _Base::_M_deallocate_map;

  /** @if maint
   *  A total of four data members accumulated down the heirarchy.  If the
   *  _Alloc type requires separate instances, then two of them will also be
   *  included in each deque.
   *  @endif
  */
  using _Base::_M_map;
  using _Base::_M_map_size;
  using _Base::_M_start;
  using _Base::_M_finish;

public:
  // [23.2.1.1] construct/copy/destroy
  // (assign() and get_allocator() are also listed in this section)
  /**
   *  @brief  Default constructor creates no elements.
  */
  explicit
  deque(const allocator_type& __a = allocator_type()) 
    : _Base(__a, 0) {}

  /**
   *  @brief  Create a %deque with copies of an exemplar element.
   *  @param  n  The number of elements to initially create.
   *  @param  value  An element to copy.
   * 
   *  This constructor fills the %deque with @a n copies of @a value.
  */
  deque(size_type __n, const value_type& __value,
        const allocator_type& __a = allocator_type())
    : _Base(__a, __n)
    { _M_fill_initialize(__value); }

  /**
   *  @brief  Create a %deque with default elements.
   *  @param  n  The number of elements to initially create.
   * 
   *  This constructor fills the %deque with @a n copies of a
   *  default-constructed element.
  */
  explicit
  deque(size_type __n)
    : _Base(allocator_type(), __n)
    { _M_fill_initialize(value_type()); }

  /**
   *  @brief  %Deque copy constructor.
   *  @param  x  A %deque of identical element and allocator types.
   * 
   *  The newly-created %deque uses a copy of the allocation object used
   *  by @a x.
  */
  deque(const deque& __x)
    : _Base(__x.get_allocator(), __x.size()) 
    { uninitialized_copy(__x.begin(), __x.end(), _M_start); }

  /**
   *  @brief  Builds a %deque from a range.
   *  @param  first  An input iterator.
   *  @param  last  An input iterator.
   * 
   *  Create a %deque consisting of copies of the elements from [first,last).
   *
   *  If the iterators are forward, bidirectional, or random-access, then
   *  this will call the elements' copy constructor N times (where N is
   *  distance(first,last)) and do no memory reallocation.  But if only
   *  input iterators are used, then this will do at most 2N calls to the
   *  copy constructor, and logN memory reallocations.
  */
  template<typename _InputIterator>
    deque(_InputIterator __first, _InputIterator __last,
          const allocator_type& __a = allocator_type())
      : _Base(__a)
    {
      // Check whether it's an integral type.  If so, it's not an iterator.
      typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
      _M_initialize_dispatch(__first, __last, _Integral());
    }

  /**
   *  The dtor only erases the elements, and note that if the elements
   *  themselves are pointers, the pointed-to memory is not touched in any
   *  way.  Managing the pointer is the user's responsibilty.
  */
  ~deque() { _Destroy(_M_start, _M_finish); }

  /**
   *  @brief  %Deque assignment operator.
   *  @param  x  A %deque of identical element and allocator types.
   * 
   *  All the elements of @a x are copied, but unlike the copy constructor, the
   *  allocator object is not copied.
  */
  deque&
  operator=(const deque& __x);

  /**
   *  @brief  Assigns a given value to a %deque.
   *  @param  n  Number of elements to be assigned.
   *  @param  val  Value to be assigned.
   *
   *  This function fills a %deque with @a n copies of the given value.
   *  Note that the assignment completely changes the %deque and that the
   *  resulting %deque's size is the same as the number of elements assigned.
   *  Old data may be lost.
  */
  void
  assign(size_type __n, const value_type& __val) { _M_fill_assign(__n, __val); }

  /**
   *  @brief  Assigns a range to a %deque.
   *  @param  first  An input iterator.
   *  @param  last   An input iterator.
   *
   *  This function fills a %deque with copies of the elements in the
   *  range [first,last).
   *
   *  Note that the assignment completely changes the %deque and that the
   *  resulting %deque's size is the same as the number of elements assigned.
   *  Old data may be lost.
  */
  template<typename _InputIterator>
    void
    assign(_InputIterator __first, _InputIterator __last)
    {
      typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
      _M_assign_dispatch(__first, __last, _Integral());
    }

  /// Get a copy of the memory allocation object.
  allocator_type
  get_allocator() const { return _Base::get_allocator(); }

  // iterators
  /**
   *  Returns a read/write iterator that points to the first element in the
   *  %deque.  Iteration is done in ordinary element order.
  */
  iterator
  begin() { return _M_start; }

  /**
   *  Returns a read-only (constant) iterator that points to the first element
   *  in the %deque.  Iteration is done in ordinary element order.
  */
  const_iterator
  begin() const { return _M_start; }

  /**
   *  Returns a read/write iterator that points one past the last element in
   *  the %deque.  Iteration is done in ordinary element order.
  */
  iterator
  end() { return _M_finish; }

  /**
   *  Returns a read-only (constant) iterator that points one past the last
   *  element in the %deque.  Iteration is done in ordinary element order.
  */
  const_iterator
  end() const { return _M_finish; }

  /**
   *  Returns a read/write reverse iterator that points to the last element in
   *  the %deque.  Iteration is done in reverse element order.
  */
  reverse_iterator
  rbegin() { return reverse_iterator(_M_finish); }

  /**
   *  Returns a read-only (constant) reverse iterator that points to the last
   *  element in the %deque.  Iteration is done in reverse element order.
  */
  const_reverse_iterator
  rbegin() const { return const_reverse_iterator(_M_finish); }

  /**
   *  Returns a read/write reverse iterator that points to one before the
   *  first element in the %deque.  Iteration is done in reverse element
   *  order.
  */
  reverse_iterator
  rend() { return reverse_iterator(_M_start); }

  /**
   *  Returns a read-only (constant) reverse iterator that points to one
   *  before the first element in the %deque.  Iteration is done in reverse
   *  element order.
  */
  const_reverse_iterator
  rend() const { return const_reverse_iterator(_M_start); }

  // [23.2.1.2] capacity
  /**  Returns the number of elements in the %deque.  */
  size_type
  size() const { return _M_finish - _M_start; }

  /**  Returns the size() of the largest possible %deque.  */
  size_type
  max_size() const { return size_type(-1); }

  /**
   *  @brief  Resizes the %deque to the specified number of elements.
   *  @param  new_size  Number of elements the %deque should contain.
   *  @param  x  Data with which new elements should be populated.
   *
   *  This function will %resize the %deque to the specified number of
   *  elements.  If the number is smaller than the %deque's current size the
   *  %deque is truncated, otherwise the %deque is extended and new elements
   *  are populated with given data.
  */
  void
  resize(size_type __new_size, const value_type& __x)
  {
    const size_type __len = size();
    if (__new_size < __len) 
      erase(_M_start + __new_size, _M_finish);
    else
      insert(_M_finish, __new_size - __len, __x);
  }

  /**
   *  @brief  Resizes the %deque to the specified number of elements.
   *  @param  new_size  Number of elements the %deque should contain.
   *
   *  This function will resize the %deque to the specified number of
   *  elements.  If the number is smaller than the %deque's current size the
   *  %deque is truncated, otherwise the %deque is extended and new elements
   *  are default-constructed.
  */
  void
  resize(size_type new_size) { resize(new_size, value_type()); }

  /**
   *  Returns true if the %deque is empty.  (Thus begin() would equal end().)
  */
  bool empty() const { return _M_finish == _M_start; }

  // element access
  /**
   *  @brief  Subscript access to the data contained in the %deque.
   *  @param  n  The index of the element for which data should be accessed.
   *  @return  Read/write reference to data.
   *
   *  This operator allows for easy, array-style, data access.
   *  Note that data access with this operator is unchecked and out_of_range
   *  lookups are not defined. (For checked lookups see at().)
  */
  reference
  operator[](size_type __n) { return _M_start[difference_type(__n)]; }

  /**
   *  @brief  Subscript access to the data contained in the %deque.
   *  @param  n  The index of the element for which data should be accessed.
   *  @return  Read-only (constant) reference to data.
   *
   *  This operator allows for easy, array-style, data access.
   *  Note that data access with this operator is unchecked and out_of_range
   *  lookups are not defined. (For checked lookups see at().)
  */
  const_reference
  operator[](size_type __n) const { return _M_start[difference_type(__n)]; }

protected:
  /// @if maint Safety check used only from at().  @endif
  void
  _M_range_check(size_type __n) const
  {
    if (__n >= this->size())
      __throw_out_of_range("deque [] access out of range");
  }

public:
  /**
   *  @brief  Provides access to the data contained in the %deque.
   *  @param  n  The index of the element for which data should be accessed.
   *  @return  Read/write reference to data.
   *  @throw  std::out_of_range  If @a n is an invalid index.
   *
   *  This function provides for safer data access.  The parameter is first
   *  checked that it is in the range of the deque.  The function throws
   *  out_of_range if the check fails.
  */
  reference
  at(size_type __n) { _M_range_check(__n); return (*this)[__n]; }

  /**
   *  @brief  Provides access to the data contained in the %deque.
   *  @param  n  The index of the element for which data should be accessed.
   *  @return  Read-only (constant) reference to data.
   *  @throw  std::out_of_range  If @a n is an invalid index.
   *
   *  This function provides for safer data access.  The parameter is first
   *  checked that it is in the range of the deque.  The function throws
   *  out_of_range if the check fails.
  */
  const_reference
  at(size_type __n) const { _M_range_check(__n); return (*this)[__n]; }

  /**
   *  Returns a read/write reference to the data at the first element of the
   *  %deque.
  */
  reference
  front() { return *_M_start; }

  /**
   *  Returns a read-only (constant) reference to the data at the first
   *  element of the %deque.
  */
  const_reference
  front() const { return *_M_start; }

  /**
   *  Returns a read/write reference to the data at the last element of the
   *  %deque.
  */
  reference
  back()
  {
    iterator __tmp = _M_finish;
    --__tmp;
    return *__tmp;
  }

  /**
   *  Returns a read-only (constant) reference to the data at the last
   *  element of the %deque.
  */
  const_reference
  back() const
  {
    const_iterator __tmp = _M_finish;
    --__tmp;
    return *__tmp;
  }

  // [23.2.1.2] modifiers
  /**
   *  @brief  Add data to the front of the %deque.
   *  @param  x  Data to be added.
   *
   *  This is a typical stack operation.  The function creates an element at
   *  the front of the %deque and assigns the given data to it.  Due to the
   *  nature of a %deque this operation can be done in constant time.
  */
  void
  push_front(const value_type& __x) 
  {
    if (_M_start._M_cur != _M_start._M_first) {
      _Construct(_M_start._M_cur - 1, __x);
      --_M_start._M_cur;
    }
    else
      _M_push_front_aux(__x);
  }

#ifdef _GLIBCPP_DEPRECATED
  /**
   *  @brief  Add data to the front of the %deque.
   *
   *  This is a typical stack operation.  The function creates a
   *  default-constructed element at the front of the %deque.  Due to the nature
   *  of a %deque this operation can be done in constant time.  You should
   *  consider using push_front(value_type()) instead.
   *
   *  @note This was deprecated in 3.2 and will be removed in 3.4.  You must
   *        define @c _GLIBCPP_DEPRECATED to make this visible in 3.2; see
   *        c++config.h.
  */
  void
  push_front()
  {
    if (_M_start._M_cur != _M_start._M_first) {
      _Construct(_M_start._M_cur - 1);
      --_M_start._M_cur;
    }
    else
      _M_push_front_aux();
  }
#endif

  /**
   *  @brief  Add data to the end of the %deque.
   *  @param  x  Data to be added.
   *
   *  This is a typical stack operation.  The function creates an element at
   *  the end of the %deque and assigns the given data to it.  Due to the
   *  nature of a %deque this operation can be done in constant time.
  */
  void
  push_back(const value_type& __x)
  {
    if (_M_finish._M_cur != _M_finish._M_last - 1) {
      _Construct(_M_finish._M_cur, __x);
      ++_M_finish._M_cur;
    }
    else
      _M_push_back_aux(__x);
  }

#ifdef _GLIBCPP_DEPRECATED
  /**
   *  @brief  Add data to the end of the %deque.
   *
   *  This is a typical stack operation.  The function creates a
   *  default-constructed element at the end of the %deque.  Due to the nature
   *  of a %deque this operation can be done in constant time.  You should
   *  consider using push_back(value_type()) instead.
   *
   *  @note This was deprecated in 3.2 and will be removed in 3.4.  You must
   *        define @c _GLIBCPP_DEPRECATED to make this visible in 3.2; see
   *        c++config.h.
  */
  void
  push_back()
  {
    if (_M_finish._M_cur != _M_finish._M_last - 1) {
      _Construct(_M_finish._M_cur);
      ++_M_finish._M_cur;
    }
    else
      _M_push_back_aux();
  }
#endif

  /**
   *  @brief  Removes first element.
   *
   *  This is a typical stack operation.  It shrinks the %deque by one.
   *
   *  Note that no data is returned, and if the first element's data is
   *  needed, it should be retrieved before pop_front() is called.
  */
  void
  pop_front()
  {
    if (_M_start._M_cur != _M_start._M_last - 1) {
      _Destroy(_M_start._M_cur);
      ++_M_start._M_cur;
    }
    else 
      _M_pop_front_aux();
  }

  /**
   *  @brief  Removes last element.
   *
   *  This is a typical stack operation.  It shrinks the %deque by one.
   *
   *  Note that no data is returned, and if the last element's data is
   *  needed, it should be retrieved before pop_back() is called.
  */
  void
  pop_back()
  {
    if (_M_finish._M_cur != _M_finish._M_first) {
      --_M_finish._M_cur;
      _Destroy(_M_finish._M_cur);
    }
    else
      _M_pop_back_aux();
  }

  /**
   *  @brief  Inserts given value into %deque before specified iterator.
   *  @param  position  An iterator into the %deque.
   *  @param  x  Data to be inserted.
   *  @return  An iterator that points to the inserted data.
   *
   *  This function will insert a copy of the given value before the specified
   *  location.
  */
  iterator
  insert(iterator position, const value_type& __x);

#ifdef _GLIBCPP_DEPRECATED
  /**
   *  @brief  Inserts an element into the %deque.
   *  @param  position  An iterator into the %deque.
   *  @return  An iterator that points to the inserted element.
   *
   *  This function will insert a default-constructed element before the
   *  specified location.  You should consider using
   *  insert(position,value_type()) instead.
   *
   *  @note This was deprecated in 3.2 and will be removed in 3.4.  You must
   *        define @c _GLIBCPP_DEPRECATED to make this visible in 3.2; see
   *        c++config.h.
  */
  iterator
  insert(iterator __position)
    { return insert(__position, value_type()); }
#endif

  /**
   *  @brief  Inserts a number of copies of given data into the %deque.
   *  @param  position  An iterator into the %deque.
   *  @param  n  Number of elements to be inserted.
   *  @param  x  Data to be inserted.
   *
   *  This function will insert a specified number of copies of the given data
   *  before the location specified by @a position.
  */
  void
  insert(iterator __position, size_type __n, const value_type& __x)
    { _M_fill_insert(__position, __n, __x); }

  /**
   *  @brief  Inserts a range into the %deque.
   *  @param  pos  An iterator into the %deque.
   *  @param  first  An input iterator.
   *  @param  last   An input iterator.
   *
   *  This function will insert copies of the data in the range [first,last)
   *  into the %deque before the location specified by @a pos.  This is
   *  known as "range insert."
  */
  template<typename _InputIterator>
    void
    insert(iterator __pos, _InputIterator __first, _InputIterator __last)
    {
      // Check whether it's an integral type.  If so, it's not an iterator.
      typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
      _M_insert_dispatch(__pos, __first, __last, _Integral());
    }

  /**
   *  @brief  Remove element at given position.
   *  @param  position  Iterator pointing to element to be erased.
   *  @return  An iterator pointing to the next element (or end()).
   *
   *  This function will erase the element at the given position and thus
   *  shorten the %deque by one.
   *
   *  The user is cautioned that
   *  this function only erases the element, and that if the element is itself
   *  a pointer, the pointed-to memory is not touched in any way.  Managing
   *  the pointer is the user's responsibilty.
  */
  iterator
  erase(iterator __position);

  /**
   *  @brief  Remove a range of elements.
   *  @param  first  Iterator pointing to the first element to be erased.
   *  @param  last  Iterator pointing to one past the last element to be erased.
   *  @return  An iterator pointing to the element pointed to by @a last
   *           prior to erasing (or end()).
   *
   *  This function will erase the elements in the range [first,last) and
   *  shorten the %deque accordingly.
   *
   *  The user is cautioned that
   *  this function only erases the elements, and that if the elements
   *  themselves are pointers, the pointed-to memory is not touched in any
   *  way.  Managing the pointer is the user's responsibilty.
  */
  iterator
  erase(iterator __first, iterator __last);

  /**
   *  @brief  Swaps data with another %deque.
   *  @param  x  A %deque of the same element and allocator types.
   *
   *  This exchanges the elements between two deques in constant time.
   *  (Four pointers, so it should be quite fast.)
   *  Note that the global std::swap() function is specialized such that
   *  std::swap(d1,d2) will feed to this function.
  */
  void
  swap(deque& __x)
  {
    std::swap(_M_start, __x._M_start);
    std::swap(_M_finish, __x._M_finish);
    std::swap(_M_map, __x._M_map);
    std::swap(_M_map_size, __x._M_map_size);
  }

  /**
   *  Erases all the elements.  Note that this function only erases the
   *  elements, and that if the elements themselves are pointers, the
   *  pointed-to memory is not touched in any way.  Managing the pointer is
   *  the user's responsibilty.
  */
  void clear(); 

protected:
  // Internal constructor functions follow.

  // called by the range constructor to implement [23.1.1]/9
  template<typename _Integer>
    void
    _M_initialize_dispatch(_Integer __n, _Integer __x, __true_type)
    {
      _M_initialize_map(__n);
      _M_fill_initialize(__x);
    }

  // called by the range constructor to implement [23.1.1]/9
  template<typename _InputIter>
    void
    _M_initialize_dispatch(_InputIter __first, _InputIter __last, __false_type)
    {
      typedef typename iterator_traits<_InputIter>::iterator_category
                       _IterCategory;
      _M_range_initialize(__first, __last, _IterCategory());
    }

  // called by the second initialize_dispatch above
  /** @{
   *  @if maint
   *  @brief Fills the deque with whatever is in [first,last).
   *  @param  first  An input iterator.
   *  @param  last  An input iterator.
   *  @return   Nothing.
   *
   *  If the iterators are actually forward iterators (or better), then the
   *  memory layout can be done all at once.  Else we move forward using
   *  push_back on each value from the iterator.
   *  @endif
  */
  template <typename _InputIterator>
    void
    _M_range_initialize(_InputIterator __first, _InputIterator __last,
                        input_iterator_tag);

  // called by the second initialize_dispatch above
  template <typename _ForwardIterator>
    void
    _M_range_initialize(_ForwardIterator __first, _ForwardIterator __last,
                        forward_iterator_tag);
  /** @} */

  /**
   *  @if maint
   *  @brief Fills the %deque with copies of value.
   *  @param  value  Initial value.
   *  @return   Nothing.
   *  @pre _M_start and _M_finish have already been initialized, but none of
   *       the %deque's elements have yet been constructed.
   *
   *  This function is called only when the user provides an explicit size
   *  (with or without an explicit exemplar value).
   *  @endif
  */
  void
  _M_fill_initialize(const value_type& __value);


  // Internal assign functions follow.  The *_aux functions do the actual
  // assignment work for the range versions.

  // called by the range assign to implement [23.1.1]/9
  template<typename _Integer>
    void
    _M_assign_dispatch(_Integer __n, _Integer __val, __true_type)
    {
      _M_fill_assign(static_cast<size_type>(__n),
                     static_cast<value_type>(__val));
    }

  // called by the range assign to implement [23.1.1]/9
  template<typename _InputIter>
    void
    _M_assign_dispatch(_InputIter __first, _InputIter __last, __false_type)
    {
      typedef typename iterator_traits<_InputIter>::iterator_category
                       _IterCategory;
      _M_assign_aux(__first, __last, _IterCategory());
    }

  // called by the second assign_dispatch above
  template <typename _InputIterator>
    void
    _M_assign_aux(_InputIterator __first, _InputIterator __last,
                  input_iterator_tag);

  // called by the second assign_dispatch above
  template <typename _ForwardIterator>
    void
    _M_assign_aux(_ForwardIterator __first, _ForwardIterator __last,
                  forward_iterator_tag)
    {
      size_type __len = distance(__first, __last);
      if (__len > size()) {
        _ForwardIterator __mid = __first;
        advance(__mid, size());
        copy(__first, __mid, begin());
        insert(end(), __mid, __last);
      }
      else
        erase(copy(__first, __last, begin()), end());
    }

  // Called by assign(n,t), and the range assign when it turns out to be the
  // same thing.
  void
  _M_fill_assign(size_type __n, const value_type& __val)
  {
    if (__n > size())
    {
      fill(begin(), end(), __val);
      insert(end(), __n - size(), __val);
    }
    else
    {
      erase(begin() + __n, end());
      fill(begin(), end(), __val);
    }
  }


  /** @{
   *  @if maint
   *  @brief Helper functions for push_* and pop_*.
   *  @endif
  */
  void _M_push_back_aux(const value_type&);
  void _M_push_front_aux(const value_type&);
#ifdef _GLIBCPP_DEPRECATED
  void _M_push_back_aux();
  void _M_push_front_aux();
#endif
  void _M_pop_back_aux();
  void _M_pop_front_aux();
  /** @} */


  // Internal insert functions follow.  The *_aux functions do the actual
  // insertion work when all shortcuts fail.

  // called by the range insert to implement [23.1.1]/9
  template<typename _Integer>
    void
    _M_insert_dispatch(iterator __pos, _Integer __n, _Integer __x, __true_type)
    {
      _M_fill_insert(__pos, static_cast<size_type>(__n),
                     static_cast<value_type>(__x));
    }

  // called by the range insert to implement [23.1.1]/9
  template<typename _InputIterator>
    void
    _M_insert_dispatch(iterator __pos,
                       _InputIterator __first, _InputIterator __last,
                       __false_type)
    {
      typedef typename iterator_traits<_InputIterator>::iterator_category
                       _IterCategory;
      _M_range_insert_aux(__pos, __first, __last, _IterCategory());
    }

  // called by the second insert_dispatch above
  template <typename _InputIterator>
    void
    _M_range_insert_aux(iterator __pos, _InputIterator __first,
                        _InputIterator __last, input_iterator_tag);

  // called by the second insert_dispatch above
  template <typename _ForwardIterator>
    void
    _M_range_insert_aux(iterator __pos, _ForwardIterator __first,
                        _ForwardIterator __last, forward_iterator_tag);

  // Called by insert(p,n,x), and the range insert when it turns out to be
  // the same thing.  Can use fill functions in optimal situations, otherwise
  // passes off to insert_aux(p,n,x).
  void
  _M_fill_insert(iterator __pos, size_type __n, const value_type& __x); 

  // called by insert(p,x)
  iterator
  _M_insert_aux(iterator __pos, const value_type& __x);

  // called by insert(p,n,x) via fill_insert
  void
  _M_insert_aux(iterator __pos, size_type __n, const value_type& __x);

  // called by range_insert_aux for forward iterators
  template <typename _ForwardIterator>
    void
    _M_insert_aux(iterator __pos, 
                  _ForwardIterator __first, _ForwardIterator __last,
                  size_type __n);

#ifdef _GLIBCPP_DEPRECATED
  // unused, see comment in implementation
  iterator _M_insert_aux(iterator __pos);
#endif

  /** @{
   *  @if maint
   *  @brief Memory-handling helpers for the previous internal insert functions.
   *  @endif
  */
  iterator
  _M_reserve_elements_at_front(size_type __n)
  {
    size_type __vacancies = _M_start._M_cur - _M_start._M_first;
    if (__n > __vacancies) 
      _M_new_elements_at_front(__n - __vacancies);
    return _M_start - difference_type(__n);
  }

  iterator
  _M_reserve_elements_at_back(size_type __n)
  {
    size_type __vacancies = (_M_finish._M_last - _M_finish._M_cur) - 1;
    if (__n > __vacancies)
      _M_new_elements_at_back(__n - __vacancies);
    return _M_finish + difference_type(__n);
  }

  void
  _M_new_elements_at_front(size_type __new_elements);

  void
  _M_new_elements_at_back(size_type __new_elements);
  /** @} */


  /** @{
   *  @if maint
   *  @brief Memory-handling helpers for the major %map.
   *
   *  Makes sure the _M_map has space for new nodes.  Does not actually add
   *  the nodes.  Can invalidate _M_map pointers.  (And consequently, %deque
   *  iterators.)
   *  @endif
  */
  void
  _M_reserve_map_at_back (size_type __nodes_to_add = 1)
  {
    if (__nodes_to_add + 1 > _M_map_size - (_M_finish._M_node - _M_map))
      _M_reallocate_map(__nodes_to_add, false);
  }

  void
  _M_reserve_map_at_front (size_type __nodes_to_add = 1)
  {
    if (__nodes_to_add > size_type(_M_start._M_node - _M_map))
      _M_reallocate_map(__nodes_to_add, true);
  }

  void
  _M_reallocate_map(size_type __nodes_to_add, bool __add_at_front);
  /** @} */
};


/**
 *  @brief  Deque equality comparison.
 *  @param  x  A %deque.
 *  @param  y  A %deque of the same type as @a x.
 *  @return  True iff the size and elements of the deques are equal.
 *
 *  This is an equivalence relation.  It is linear in the size of the
 *  deques.  Deques are considered equivalent if their sizes are equal,
 *  and if corresponding elements compare equal.
*/
template <typename _Tp, typename _Alloc>
inline bool operator==(const deque<_Tp, _Alloc>& __x,
                       const deque<_Tp, _Alloc>& __y)
{
  return __x.size() == __y.size() &&
         equal(__x.begin(), __x.end(), __y.begin());
}

/**
 *  @brief  Deque ordering relation.
 *  @param  x  A %deque.
 *  @param  y  A %deque of the same type as @a x.
 *  @return  True iff @a x is lexographically less than @a y.
 *
 *  This is a total ordering relation.  It is linear in the size of the
 *  deques.  The elements must be comparable with @c <.
 *
 *  See std::lexographical_compare() for how the determination is made.
*/
template <typename _Tp, typename _Alloc>
inline bool operator<(const deque<_Tp, _Alloc>& __x,
                      const deque<_Tp, _Alloc>& __y)
{
  return lexicographical_compare(__x.begin(), __x.end(), 
                                 __y.begin(), __y.end());
}

/// Based on operator==
template <typename _Tp, typename _Alloc>
inline bool operator!=(const deque<_Tp, _Alloc>& __x,
                       const deque<_Tp, _Alloc>& __y) {
  return !(__x == __y);
}

/// Based on operator<
template <typename _Tp, typename _Alloc>
inline bool operator>(const deque<_Tp, _Alloc>& __x,
                      const deque<_Tp, _Alloc>& __y) {
  return __y < __x;
}

/// Based on operator<
template <typename _Tp, typename _Alloc>
inline bool operator<=(const deque<_Tp, _Alloc>& __x,
                       const deque<_Tp, _Alloc>& __y) {
  return !(__y < __x);
}

/// Based on operator<
template <typename _Tp, typename _Alloc>
inline bool operator>=(const deque<_Tp, _Alloc>& __x,
                       const deque<_Tp, _Alloc>& __y) {
  return !(__x < __y);
}

/// See std::deque::swap().
template <typename _Tp, typename _Alloc>
inline void swap(deque<_Tp,_Alloc>& __x, deque<_Tp,_Alloc>& __y)
{
  __x.swap(__y);
}

} // namespace std 
  
#endif /* __GLIBCPP_INTERNAL_DEQUE_H */