_Tp** __nstart = _M_map + (_M_map_size - __num_nodes) / 2;
  _Tp** __nfinish = __nstart + __num_nodes;
    
  __STL_TRY {
    _M_create_nodes(__nstart, __nfinish);
  }
  __STL_UNWIND((_M_deallocate_map(_M_map, _M_map_size), 
                _M_map = 0, _M_map_size = 0));
  _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(__bufsiz, sizeof(_Tp));
}

template <class _Tp, class _Alloc, size_t __bufsiz>
void
_Deque_base<_Tp,_Alloc,__bufsiz>::_M_create_nodes(_Tp** __nstart,
                                                  _Tp** __nfinish)
{
  _Tp** __cur;
  __STL_TRY {
    for (__cur = __nstart; __cur < __nfinish; ++__cur)
      *__cur = _M_allocate_node();
  }
  __STL_UNWIND(_M_destroy_nodes(__nstart, __cur));
}

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

// See __deque_buf_size().  The only reason that the default value is 0
//  is as a workaround for bugs in the way that some compilers handle
//  constant expressions.
template <class _Tp, class _Alloc = __STL_DEFAULT_ALLOCATOR(_Tp), 
          size_t __bufsiz = 0> 
class deque : protected _Deque_base<_Tp, _Alloc, __bufsiz> {
  typedef _Deque_base<_Tp, _Alloc, __bufsiz> _Base;
public:                         // Basic types
  typedef _Tp value_type;
  typedef value_type* pointer;
  typedef const value_type* const_pointer;
  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;
  allocator_type get_allocator() const { return _Base::get_allocator(); }

public:                         // Iterators
  typedef typename _Base::iterator       iterator;
  typedef typename _Base::const_iterator const_iterator;

#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION
  typedef reverse_iterator<const_iterator> const_reverse_iterator;
  typedef reverse_iterator<iterator> reverse_iterator;
#else /* __STL_CLASS_PARTIAL_SPECIALIZATION */
  typedef reverse_iterator<const_iterator, value_type, const_reference, 
                           difference_type>  
          const_reverse_iterator;
  typedef reverse_iterator<iterator, value_type, reference, difference_type>
          reverse_iterator; 
#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */

protected:                      // Internal typedefs
  typedef pointer* _Map_pointer;
  static size_t _S_buffer_size()
    { return __deque_buf_size(__bufsiz, sizeof(_Tp)); }

protected:
#ifdef __STL_USE_NAMESPACES
  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;

  using _Base::_M_map;
  using _Base::_M_map_size;
  using _Base::_M_start;
  using _Base::_M_finish;
#endif /* __STL_USE_NAMESPACES */

public:                         // Basic accessors
  iterator begin() { return _M_start; }
  iterator end() { return _M_finish; }
  const_iterator begin() const { return _M_start; }
  const_iterator end() const { return _M_finish; }

  reverse_iterator rbegin() { return reverse_iterator(_M_finish); }
  reverse_iterator rend() { return reverse_iterator(_M_start); }
  const_reverse_iterator rbegin() const 
    { return const_reverse_iterator(_M_finish); }
  const_reverse_iterator rend() const 
    { return const_reverse_iterator(_M_start); }

  reference operator[](size_type __n)
    { return _M_start[difference_type(__n)]; }
  const_reference operator[](size_type __n) const 
    { return _M_start[difference_type(__n)]; }

#ifdef __STL_THROW_RANGE_ERRORS
  void _M_range_check(size_type __n) const {
    if (__n >= this->size())
      __stl_throw_range_error("deque");
  }

  reference at(size_type __n)
    { _M_range_check(__n); return (*this)[__n]; }
  const_reference at(size_type __n) const
    { _M_range_check(__n); return (*this)[__n]; }
#endif /* __STL_THROW_RANGE_ERRORS */

  reference front() { return *_M_start; }
  reference back() {
    iterator __tmp = _M_finish;
    --__tmp;
    return *__tmp;
  }
  const_reference front() const { return *_M_start; }
  const_reference back() const {
    const_iterator __tmp = _M_finish;
    --__tmp;
    return *__tmp;
  }

  size_type size() const { return _M_finish - _M_start; }
  size_type max_size() const { return size_type(-1); }
  bool empty() const { return _M_finish == _M_start; }

public:                         // Constructor, destructor.
  explicit deque(const allocator_type& __a = allocator_type()) 
    : _Base(__a, 0) {}
  deque(const deque& __x) : _Base(__x.get_allocator(), __x.size()) 
    { uninitialized_copy(__x.begin(), __x.end(), _M_start); }
  deque(size_type __n, const value_type& __value,
        const allocator_type& __a = allocator_type()) : _Base(__a, __n)
    { _M_fill_initialize(__value); }
  explicit deque(size_type __n) : _Base(allocator_type(), __n)
    { _M_fill_initialize(value_type()); }

#ifdef __STL_MEMBER_TEMPLATES

  // Check whether it's an integral type.  If so, it's not an iterator.
  template <class _InputIterator>
  deque(_InputIterator __first, _InputIterator __last,
        const allocator_type& __a = allocator_type()) : _Base(__a) {
    typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
    _M_initialize_dispatch(__first, __last, _Integral());
  }

  template <class _Integer>
  void _M_initialize_dispatch(_Integer __n, _Integer __x, __true_type) {
    _M_initialize_map(__n);
    _M_fill_initialize(__x);
  }

  template <class _InputIter>
  void _M_initialize_dispatch(_InputIter __first, _InputIter __last,
                              __false_type) {
    _M_range_initialize(__first, __last, __ITERATOR_CATEGORY(__first));
  }

#else /* __STL_MEMBER_TEMPLATES */

  deque(const value_type* __first, const value_type* __last,
        const allocator_type& __a = allocator_type()) 
    : _Base(__a, __last - __first)
    { uninitialized_copy(__first, __last, _M_start); }
  deque(const_iterator __first, const_iterator __last,
        const allocator_type& __a = allocator_type()) 
    : _Base(__a, __last - __first)
    { uninitialized_copy(__first, __last, _M_start); }

#endif /* __STL_MEMBER_TEMPLATES */

  ~deque() { destroy(_M_start, _M_finish); }

  deque& operator= (const deque& __x) {
    const size_type __len = size();
    if (&__x != this) {
      if (__len >= __x.size())
        erase(copy(__x.begin(), __x.end(), _M_start), _M_finish);
      else {
        const_iterator __mid = __x.begin() + difference_type(__len);
        copy(__x.begin(), __mid, _M_start);
        insert(_M_finish, __mid, __x.end());
      }
    }
    return *this;
  }        

  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);
  }

public: 
  // assign(), a generalized assignment member function.  Two
  // versions: one that takes a count, and one that takes a range.
  // The range version is a member template, so we dispatch on whether
  // or not the type is an integer.

  void _M_fill_assign(size_type __n, const _Tp& __val) {
    if (__n > size()) {
      fill(begin(), end(), __val);
      insert(end(), __n - size(), __val);
    }
    else {
      erase(begin() + __n, end());
      fill(begin(), end(), __val);
    }
  }

  void assign(size_type __n, const _Tp& __val) {
    _M_fill_assign(__n, __val);
  }

#ifdef __STL_MEMBER_TEMPLATES

  template <class _InputIterator>
  void assign(_InputIterator __first, _InputIterator __last) {
    typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
    _M_assign_dispatch(__first, __last, _Integral());
  }

private:                        // helper functions for assign() 

  template <class _Integer>
  void _M_assign_dispatch(_Integer __n, _Integer __val, __true_type)
    { _M_fill_assign((size_type) __n, (_Tp) __val); }

  template <class _InputIterator>
  void _M_assign_dispatch(_InputIterator __first, _InputIterator __last,
                          __false_type) {
    _M_assign_aux(__first, __last, __ITERATOR_CATEGORY(__first));
  }

  template <class _InputIterator>
  void _M_assign_aux(_InputIterator __first, _InputIterator __last,
                     input_iterator_tag);

  template <class _ForwardIterator>
  void _M_assign_aux(_ForwardIterator __first, _ForwardIterator __last,
                     forward_iterator_tag) {
    size_type __len = 0;
    distance(__first, __last, __len);
    if (__len > size()) {
      _ForwardIterator __mid = __first;
      advance(__mid, size());
      copy(__first, __mid, begin());
      insert(end(), __mid, __last);
    }
    else
      erase(copy(__first, __last, begin()), end());
  }

#endif /* __STL_MEMBER_TEMPLATES */

public:                         // push_* and pop_*
  
  void push_back(const value_type& __t) {
    if (_M_finish._M_cur != _M_finish._M_last - 1) {
      construct(_M_finish._M_cur, __t);
      ++_M_finish._M_cur;
    }
    else
      _M_push_back_aux(__t);
  }

  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();
  }

  void push_front(const value_type& __t) {
    if (_M_start._M_cur != _M_start._M_first) {
      construct(_M_start._M_cur - 1, __t);
      --_M_start._M_cur;
    }
    else
      _M_push_front_aux(__t);
  }

  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();
  }


  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();
  }

  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();
  }

public:                         // Insert

  iterator insert(iterator position, const value_type& __x) {
    if (position._M_cur == _M_start._M_cur) {
      push_front(__x);
      return _M_start;
    }
    else if (position._M_cur == _M_finish._M_cur) {
      push_back(__x);
      iterator __tmp = _M_finish;
      --__tmp;
      return __tmp;
    }
    else {
      return _M_insert_aux(position, __x);
    }
  }

  iterator insert(iterator __position)
    { return insert(__position, value_type()); }

  void insert(iterator __pos, size_type __n, const value_type& __x)
    { _M_fill_insert(__pos, __n, __x); }

  void _M_fill_insert(iterator __pos, size_type __n, const value_type& __x); 

#ifdef __STL_MEMBER_TEMPLATES  

  // Check whether it's an integral type.  If so, it's not an iterator.
  template <class _InputIterator>
  void insert(iterator __pos, _InputIterator __first, _InputIterator __last) {
    typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
    _M_insert_dispatch(__pos, __first, __last, _Integral());
  }

  template <class _Integer>
  void _M_insert_dispatch(iterator __pos, _Integer __n, _Integer __x,
                          __true_type) {
    _M_fill_insert(__pos, (size_type) __n, (value_type) __x);
  }

  template <class _InputIterator>
  void _M_insert_dispatch(iterator __pos,
                          _InputIterator __first, _InputIterator __last,
                          __false_type) {
    insert(__pos, __first, __last, __ITERATOR_CATEGORY(__first));
  }

#else /* __STL_MEMBER_TEMPLATES */

  void insert(iterator __pos,
              const value_type* __first, const value_type* __last);
  void insert(iterator __pos,
              const_iterator __first, const_iterator __last);

#endif /* __STL_MEMBER_TEMPLATES */

  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);
  }

  void resize(size_type new_size) { resize(new_size, value_type()); }

public:                         // Erase
  iterator erase(iterator __pos) {
    iterator __next = __pos;
    ++__next;
    difference_type __index = __pos - _M_start;
    if (__index < (size() >> 1)) {
      copy_backward(_M_start, __pos, __next);
      pop_front();
    }
    else {
      copy(__next, _M_finish, __pos);
      pop_back();
    }
    return _M_start + __index;
  }

  iterator erase(iterator __first, iterator __last);
  void clear(); 

protected:                        // Internal construction/destruction

  void _M_fill_initialize(const value_type& __value);

#ifdef __STL_MEMBER_TEMPLATES  

  template <class _InputIterator>
  void _M_range_initialize(_InputIterator __first, _InputIterator __last,
                        input_iterator_tag);

  template <class _ForwardIterator>
  void _M_range_initialize(_ForwardIterator __first, _ForwardIterator __last,
                        forward_iterator_tag);

#endif /* __STL_MEMBER_TEMPLATES */

protected:                        // Internal push_* and pop_*

  void _M_push_back_aux(const value_type&);
  void _M_push_back_aux();
  void _M_push_front_aux(const value_type&);
  void _M_push_front_aux();
  void _M_pop_back_aux();
  void _M_pop_front_aux();

protected:                        // Internal insert functions

#ifdef __STL_MEMBER_TEMPLATES  

  template <class _InputIterator>