// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP_DEQUE
#define _LIBCPP_DEQUE

/*
    deque synopsis

namespace std
{

template <class T, class Allocator = allocator<T> >
class deque
{
public:
    // types:
    typedef T value_type;
    typedef Allocator allocator_type;

    typedef typename allocator_type::reference       reference;
    typedef typename allocator_type::const_reference const_reference;
    typedef implementation-defined                   iterator;
    typedef implementation-defined                   const_iterator;
    typedef typename allocator_type::size_type       size_type;
    typedef typename allocator_type::difference_type difference_type;

    typedef typename allocator_type::pointer         pointer;
    typedef typename allocator_type::const_pointer   const_pointer;
    typedef std::reverse_iterator<iterator>          reverse_iterator;
    typedef std::reverse_iterator<const_iterator>    const_reverse_iterator;

    // construct/copy/destroy:
    deque() noexcept(is_nothrow_default_constructible<allocator_type>::value);
    explicit deque(const allocator_type& a);
    explicit deque(size_type n);
    explicit deque(size_type n, const allocator_type& a); // C++14
    deque(size_type n, const value_type& v);
    deque(size_type n, const value_type& v, const allocator_type& a);
    template <class InputIterator>
        deque(InputIterator f, InputIterator l);
    template <class InputIterator>
        deque(InputIterator f, InputIterator l, const allocator_type& a);
    deque(const deque& c);
    deque(deque&& c)
        noexcept(is_nothrow_move_constructible<allocator_type>::value);
    deque(initializer_list<value_type> il, const Allocator& a = allocator_type());
    deque(const deque& c, const allocator_type& a);
    deque(deque&& c, const allocator_type& a);
    ~deque();

    deque& operator=(const deque& c);
    deque& operator=(deque&& c)
        noexcept(
             allocator_type::propagate_on_container_move_assignment::value &&
             is_nothrow_move_assignable<allocator_type>::value);
    deque& operator=(initializer_list<value_type> il);

    template <class InputIterator>
        void assign(InputIterator f, InputIterator l);
    void assign(size_type n, const value_type& v);
    void assign(initializer_list<value_type> il);

    allocator_type get_allocator() const noexcept;

    // iterators:

    iterator       begin() noexcept;
    const_iterator begin() const noexcept;
    iterator       end() noexcept;
    const_iterator end() const noexcept;

    reverse_iterator       rbegin() noexcept;
    const_reverse_iterator rbegin() const noexcept;
    reverse_iterator       rend() noexcept;
    const_reverse_iterator rend() const noexcept;

    const_iterator         cbegin() const noexcept;
    const_iterator         cend() const noexcept;
    const_reverse_iterator crbegin() const noexcept;
    const_reverse_iterator crend() const noexcept;

    // capacity:
    size_type size() const noexcept;
    size_type max_size() const noexcept;
    void resize(size_type n);
    void resize(size_type n, const value_type& v);
    void shrink_to_fit();
    bool empty() const noexcept;

    // element access:
    reference operator[](size_type i);
    const_reference operator[](size_type i) const;
    reference at(size_type i);
    const_reference at(size_type i) const;
    reference front();
    const_reference front() const;
    reference back();
    const_reference back() const;

    // modifiers:
    void push_front(const value_type& v);
    void push_front(value_type&& v);
    void push_back(const value_type& v);
    void push_back(value_type&& v);
    template <class... Args> reference emplace_front(Args&&... args);  // reference in C++17
    template <class... Args> reference emplace_back(Args&&... args);   // reference in C++17
    template <class... Args> iterator emplace(const_iterator p, Args&&... args);
    iterator insert(const_iterator p, const value_type& v);
    iterator insert(const_iterator p, value_type&& v);
    iterator insert(const_iterator p, size_type n, const value_type& v);
    template <class InputIterator>
        iterator insert(const_iterator p, InputIterator f, InputIterator l);
    iterator insert(const_iterator p, initializer_list<value_type> il);
    void pop_front();
    void pop_back();
    iterator erase(const_iterator p);
    iterator erase(const_iterator f, const_iterator l);
    void swap(deque& c)
        noexcept(allocator_traits<allocator_type>::is_always_equal::value);  // C++17
    void clear() noexcept;
};

template <class InputIterator, class Allocator = allocator<typename iterator_traits<InputIterator>::value_type>>
   deque(InputIterator, InputIterator, Allocator = Allocator())
   -> deque<typename iterator_traits<InputIterator>::value_type, Allocator>; // C++17

template <class T, class Allocator>
    bool operator==(const deque<T,Allocator>& x, const deque<T,Allocator>& y);
template <class T, class Allocator>
    bool operator< (const deque<T,Allocator>& x, const deque<T,Allocator>& y);
template <class T, class Allocator>
    bool operator!=(const deque<T,Allocator>& x, const deque<T,Allocator>& y);
template <class T, class Allocator>
    bool operator> (const deque<T,Allocator>& x, const deque<T,Allocator>& y);
template <class T, class Allocator>
    bool operator>=(const deque<T,Allocator>& x, const deque<T,Allocator>& y);
template <class T, class Allocator>
    bool operator<=(const deque<T,Allocator>& x, const deque<T,Allocator>& y);

// specialized algorithms:
template <class T, class Allocator>
    void swap(deque<T,Allocator>& x, deque<T,Allocator>& y)
         noexcept(noexcept(x.swap(y)));

template <class T, class Allocator, class U>
    typename deque<T, Allocator>::size_type
    erase(deque<T, Allocator>& c, const U& value);       // C++20
template <class T, class Allocator, class Predicate>
    typename deque<T, Allocator>::size_type
    erase_if(deque<T, Allocator>& c, Predicate pred);    // C++20

}  // std

*/

#include <__algorithm/copy.h>
#include <__algorithm/copy_backward.h>
#include <__algorithm/equal.h>
#include <__algorithm/fill_n.h>
#include <__algorithm/lexicographical_compare.h>
#include <__algorithm/min.h>
#include <__algorithm/remove.h>
#include <__algorithm/remove_if.h>
#include <__algorithm/unwrap_iter.h>
#include <__assert> // all public C++ headers provide the assertion handler
#include <__config>
#include <__format/enable_insertable.h>
#include <__iterator/iterator_traits.h>
#include <__iterator/next.h>
#include <__iterator/prev.h>
#include <__iterator/reverse_iterator.h>
#include <__memory/allocator_destructor.h>
#include <__memory/pointer_traits.h>
#include <__memory/temp_value.h>
#include <__memory/unique_ptr.h>
#include <__memory_resource/polymorphic_allocator.h>
#include <__split_buffer>
#include <__type_traits/is_allocator.h>
#include <__utility/forward.h>
#include <__utility/move.h>
#include <__utility/swap.h>
#include <limits>
#include <stdexcept>
#include <type_traits>
#include <version>

// standard-mandated includes

// [iterator.range]
#include <__iterator/access.h>
#include <__iterator/data.h>
#include <__iterator/empty.h>
#include <__iterator/reverse_access.h>
#include <__iterator/size.h>

// [deque.syn]
#include <compare>
#include <initializer_list>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>


_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Tp, class _Allocator = allocator<_Tp> > class _LIBCPP_TEMPLATE_VIS deque;

template <class _ValueType, class _Pointer, class _Reference, class _MapPointer,
          class _DiffType, _DiffType _BlockSize>
class _LIBCPP_TEMPLATE_VIS __deque_iterator;

template <class _RAIter,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
copy(_RAIter __f,
     _RAIter __l,
     __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
     typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type* = 0);

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _OutputIterator>
_LIBCPP_HIDE_FROM_ABI _OutputIterator
copy(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
     __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
     _OutputIterator __r);

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
copy(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
     __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
     __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r);

template <class _RAIter,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
copy_backward(_RAIter __f,
              _RAIter __l,
              __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
              typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type* = 0);

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _OutputIterator>
_LIBCPP_HIDE_FROM_ABI _OutputIterator
copy_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
              __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
              _OutputIterator __r);

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
copy_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
              __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
              __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r);

template <class _RAIter,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
move(_RAIter __f,
     _RAIter __l,
     __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
     typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type* = 0);

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _OutputIterator>
_LIBCPP_HIDE_FROM_ABI _OutputIterator
move(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
     __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
     _OutputIterator __r);

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
move(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
     __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
     __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r);

template <class _RAIter,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
move_backward(_RAIter __f,
              _RAIter __l,
              __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
              typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type* = 0);

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _OutputIterator>
_LIBCPP_HIDE_FROM_ABI _OutputIterator
move_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
              __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
              _OutputIterator __r);

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
move_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
              __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
              __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r);

template <class _ValueType, class _DiffType>
struct __deque_block_size {
  static const _DiffType value = sizeof(_ValueType) < 256 ? 4096 / sizeof(_ValueType) : 16;
};

template <class _ValueType, class _Pointer, class _Reference, class _MapPointer,
          class _DiffType, _DiffType _BS =
#ifdef _LIBCPP_ABI_INCOMPLETE_TYPES_IN_DEQUE
// Keep template parameter to avoid changing all template declarations thoughout
// this file.
                               0
#else
                               __deque_block_size<_ValueType, _DiffType>::value
#endif
          >
class _LIBCPP_TEMPLATE_VIS __deque_iterator
{
    typedef _MapPointer __map_iterator;
public:
    typedef _Pointer  pointer;
    typedef _DiffType difference_type;
private:
    __map_iterator __m_iter_;
    pointer        __ptr_;

    static const difference_type __block_size;
public:
    typedef _ValueType                  value_type;
    typedef random_access_iterator_tag  iterator_category;
    typedef _Reference                  reference;

    _LIBCPP_HIDE_FROM_ABI __deque_iterator() _NOEXCEPT
#if _LIBCPP_STD_VER > 11
     : __m_iter_(nullptr), __ptr_(nullptr)
#endif
     {}

    template <class _Pp, class _Rp, class _MP>
    _LIBCPP_HIDE_FROM_ABI
    __deque_iterator(const __deque_iterator<value_type, _Pp, _Rp, _MP, difference_type, _BS>& __it,
                typename enable_if<is_convertible<_Pp, pointer>::value>::type* = 0) _NOEXCEPT
        : __m_iter_(__it.__m_iter_), __ptr_(__it.__ptr_) {}

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

    _LIBCPP_HIDE_FROM_ABI __deque_iterator& operator++()
    {
        if (++__ptr_ - *__m_iter_ == __block_size)
        {
            ++__m_iter_;
            __ptr_ = *__m_iter_;
        }
        return *this;
    }

    _LIBCPP_HIDE_FROM_ABI __deque_iterator operator++(int)
    {
        __deque_iterator __tmp = *this;
        ++(*this);
        return __tmp;
    }

    _LIBCPP_HIDE_FROM_ABI __deque_iterator& operator--()
    {
        if (__ptr_ == *__m_iter_)
        {
            --__m_iter_;
            __ptr_ = *__m_iter_ + __block_size;
        }
        --__ptr_;
        return *this;
    }

    _LIBCPP_HIDE_FROM_ABI __deque_iterator operator--(int)
    {
        __deque_iterator __tmp = *this;
        --(*this);
        return __tmp;
    }

    _LIBCPP_HIDE_FROM_ABI __deque_iterator& operator+=(difference_type __n)
    {
        if (__n != 0)
        {
            __n += __ptr_ - *__m_iter_;
            if (__n > 0)
            {
                __m_iter_ += __n / __block_size;
                __ptr_ = *__m_iter_ + __n % __block_size;
            }
            else // (__n < 0)
            {
                difference_type __z = __block_size - 1 - __n;
                __m_iter_ -= __z / __block_size;
                __ptr_ = *__m_iter_ + (__block_size - 1 - __z % __block_size);
            }
        }
        return *this;
    }

    _LIBCPP_HIDE_FROM_ABI __deque_iterator& operator-=(difference_type __n)
    {
        return *this += -__n;
    }

    _LIBCPP_HIDE_FROM_ABI __deque_iterator operator+(difference_type __n) const
    {
        __deque_iterator __t(*this);
        __t += __n;
        return __t;
    }

    _LIBCPP_HIDE_FROM_ABI __deque_iterator operator-(difference_type __n) const
    {
        __deque_iterator __t(*this);
        __t -= __n;
        return __t;
    }

    _LIBCPP_HIDE_FROM_ABI
    friend __deque_iterator operator+(difference_type __n, const __deque_iterator& __it)
        {return __it + __n;}

    _LIBCPP_HIDE_FROM_ABI
    friend difference_type operator-(const __deque_iterator& __x, const __deque_iterator& __y)
    {
        if (__x != __y)
            return (__x.__m_iter_ - __y.__m_iter_) * __block_size
                 + (__x.__ptr_ - *__x.__m_iter_)
                 - (__y.__ptr_ - *__y.__m_iter_);
        return 0;
    }

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

    _LIBCPP_HIDE_FROM_ABI friend
        bool operator==(const __deque_iterator& __x, const __deque_iterator& __y)
        {return __x.__ptr_ == __y.__ptr_;}

    _LIBCPP_HIDE_FROM_ABI friend
        bool operator!=(const __deque_iterator& __x, const __deque_iterator& __y)
        {return !(__x == __y);}

    _LIBCPP_HIDE_FROM_ABI friend
        bool operator<(const __deque_iterator& __x, const __deque_iterator& __y)
        {return __x.__m_iter_ < __y.__m_iter_ ||
               (__x.__m_iter_ == __y.__m_iter_ && __x.__ptr_ < __y.__ptr_);}

    _LIBCPP_HIDE_FROM_ABI friend
        bool operator>(const __deque_iterator& __x, const __deque_iterator& __y)
        {return __y < __x;}

    _LIBCPP_HIDE_FROM_ABI friend
        bool operator<=(const __deque_iterator& __x, const __deque_iterator& __y)
        {return !(__y < __x);}

    _LIBCPP_HIDE_FROM_ABI friend
        bool operator>=(const __deque_iterator& __x, const __deque_iterator& __y)
        {return !(__x < __y);}

private:
    _LIBCPP_HIDE_FROM_ABI explicit __deque_iterator(__map_iterator __m, pointer __p) _NOEXCEPT
        : __m_iter_(__m), __ptr_(__p) {}

    template <class _Tp, class _Ap> friend class _LIBCPP_TEMPLATE_VIS deque;
    template <class _Vp, class _Pp, class _Rp, class _MP, class _Dp, _Dp>
        friend class _LIBCPP_TEMPLATE_VIS __deque_iterator;

    template <class _RAIter,
              class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
    friend
    __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
    copy(_RAIter __f,
         _RAIter __l,
         __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
         typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type*);

    template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
              class _OutputIterator>
    friend
    _OutputIterator
    copy(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
         __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
         _OutputIterator __r);

    template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
              class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
    friend
    __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
    copy(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
         __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
         __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r);

    template <class _RAIter,
              class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
    friend
    __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
    copy_backward(_RAIter __f,
                  _RAIter __l,
                  __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
                  typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type*);

    template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
              class _OutputIterator>
    friend
    _OutputIterator
    copy_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
                  __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
                  _OutputIterator __r);

    template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
              class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
    friend
    __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
    copy_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
                  __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
                  __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r);

    template <class _RAIter,
              class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
    friend
    __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
    move(_RAIter __f,
         _RAIter __l,
         __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
         typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type*);

    template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
              class _OutputIterator>
    friend
    _OutputIterator
    move(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
         __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
         _OutputIterator __r);

    template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
              class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
    friend
    __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
    move(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
         __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
         __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r);

    template <class _RAIter,
              class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
    friend
    __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
    move_backward(_RAIter __f,
                  _RAIter __l,
                  __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
                  typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type*);

    template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
              class _OutputIterator>
    friend
    _OutputIterator
    move_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
                  __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
                  _OutputIterator __r);

    template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
              class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
    friend
    __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
    move_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
                  __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
                  __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r);
};

template <class _ValueType, class _Pointer, class _Reference, class _MapPointer,
          class _DiffType, _DiffType _BlockSize>
const _DiffType __deque_iterator<_ValueType, _Pointer, _Reference, _MapPointer,
                                 _DiffType, _BlockSize>::__block_size =
    __deque_block_size<_ValueType, _DiffType>::value;

// copy

template <class _RAIter,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
copy(_RAIter __f,
     _RAIter __l,
     __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
     typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type*)
{
    typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::difference_type difference_type;
    typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::pointer pointer;
    const difference_type __block_size = __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::__block_size;
    while (__f != __l)
    {
        pointer __rb = __r.__ptr_;
        pointer __re = *__r.__m_iter_ + __block_size;
        difference_type __bs = __re - __rb;
        difference_type __n = __l - __f;
        _RAIter __m = __l;
        if (__n > __bs)
        {
            __n = __bs;
            __m = __f + __n;
        }
        _VSTD::copy(__f, __m, __rb);
        __f = __m;
        __r += __n;
    }
    return __r;
}

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _OutputIterator>
_LIBCPP_HIDE_FROM_ABI _OutputIterator
copy(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
     __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
     _OutputIterator __r)
{
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
    const difference_type __block_size = __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::__block_size;
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        pointer __fb = __f.__ptr_;
        pointer __fe = *__f.__m_iter_ + __block_size;
        difference_type __bs = __fe - __fb;
        if (__bs > __n)
        {
            __bs = __n;
            __fe = __fb + __bs;
        }
        __r = _VSTD::copy(__fb, __fe, __r);
        __n -= __bs;
        __f += __bs;
    }
    return __r;
}

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
copy(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
     __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
     __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r)
{
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
    const difference_type __block_size = __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::__block_size;
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        pointer __fb = __f.__ptr_;
        pointer __fe = *__f.__m_iter_ + __block_size;
        difference_type __bs = __fe - __fb;
        if (__bs > __n)
        {
            __bs = __n;
            __fe = __fb + __bs;
        }
        __r = _VSTD::copy(__fb, __fe, __r);
        __n -= __bs;
        __f += __bs;
    }
    return __r;
}

// copy_backward

template <class _RAIter,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
copy_backward(_RAIter __f,
              _RAIter __l,
              __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
              typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type*)
{
    typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::difference_type difference_type;
    typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::pointer pointer;
    while (__f != __l)
    {
        __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __rp = _VSTD::prev(__r);
        pointer __rb = *__rp.__m_iter_;
        pointer __re = __rp.__ptr_ + 1;
        difference_type __bs = __re - __rb;
        difference_type __n = __l - __f;
        _RAIter __m = __f;
        if (__n > __bs)
        {
            __n = __bs;
            __m = __l - __n;
        }
        _VSTD::copy_backward(__m, __l, __re);
        __l = __m;
        __r -= __n;
    }
    return __r;
}

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _OutputIterator>
_LIBCPP_HIDE_FROM_ABI _OutputIterator
copy_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
              __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
              _OutputIterator __r)
{
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        --__l;
        pointer __lb = *__l.__m_iter_;
        pointer __le = __l.__ptr_ + 1;
        difference_type __bs = __le - __lb;
        if (__bs > __n)
        {
            __bs = __n;
            __lb = __le - __bs;
        }
        __r = _VSTD::copy_backward(__lb, __le, __r);
        __n -= __bs;
        __l -= __bs - 1;
    }
    return __r;
}

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
copy_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
              __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
              __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r)
{
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        --__l;
        pointer __lb = *__l.__m_iter_;
        pointer __le = __l.__ptr_ + 1;
        difference_type __bs = __le - __lb;
        if (__bs > __n)
        {
            __bs = __n;
            __lb = __le - __bs;
        }
        __r = _VSTD::copy_backward(__lb, __le, __r);
        __n -= __bs;
        __l -= __bs - 1;
    }
    return __r;
}

// move

template <class _RAIter,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
move(_RAIter __f,
     _RAIter __l,
     __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
     typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type*)
{
    typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::difference_type difference_type;
    typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::pointer pointer;
    const difference_type __block_size = __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::__block_size;
    while (__f != __l)
    {
        pointer __rb = __r.__ptr_;
        pointer __re = *__r.__m_iter_ + __block_size;
        difference_type __bs = __re - __rb;
        difference_type __n = __l - __f;
        _RAIter __m = __l;
        if (__n > __bs)
        {
            __n = __bs;
            __m = __f + __n;
        }
        _VSTD::move(__f, __m, __rb);
        __f = __m;
        __r += __n;
    }
    return __r;
}

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _OutputIterator>
_LIBCPP_HIDE_FROM_ABI _OutputIterator
move(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
     __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
     _OutputIterator __r)
{
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
    const difference_type __block_size = __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::__block_size;
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        pointer __fb = __f.__ptr_;
        pointer __fe = *__f.__m_iter_ + __block_size;
        difference_type __bs = __fe - __fb;
        if (__bs > __n)
        {
            __bs = __n;
            __fe = __fb + __bs;
        }
        __r = _VSTD::move(__fb, __fe, __r);
        __n -= __bs;
        __f += __bs;
    }
    return __r;
}

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
move(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
     __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
     __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r)
{
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
    const difference_type __block_size = __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::__block_size;
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        pointer __fb = __f.__ptr_;
        pointer __fe = *__f.__m_iter_ + __block_size;
        difference_type __bs = __fe - __fb;
        if (__bs > __n)
        {
            __bs = __n;
            __fe = __fb + __bs;
        }
        __r = _VSTD::move(__fb, __fe, __r);
        __n -= __bs;
        __f += __bs;
    }
    return __r;
}

// move_backward

template <class _RAIter,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
move_backward(_RAIter __f,
              _RAIter __l,
              __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r,
              typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type*)
{
    typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::difference_type difference_type;
    typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::pointer pointer;
    while (__f != __l)
    {
        __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __rp = _VSTD::prev(__r);
        pointer __rb = *__rp.__m_iter_;
        pointer __re = __rp.__ptr_ + 1;
        difference_type __bs = __re - __rb;
        difference_type __n = __l - __f;
        _RAIter __m = __f;
        if (__n > __bs)
        {
            __n = __bs;
            __m = __l - __n;
        }
        _VSTD::move_backward(__m, __l, __re);
        __l = __m;
        __r -= __n;
    }
    return __r;
}

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _OutputIterator>
_LIBCPP_HIDE_FROM_ABI _OutputIterator
move_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
              __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
              _OutputIterator __r)
{
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        --__l;
        pointer __lb = *__l.__m_iter_;
        pointer __le = __l.__ptr_ + 1;
        difference_type __bs = __le - __lb;
        if (__bs > __n)
        {
            __bs = __n;
            __lb = __le - __bs;
        }
        __r = _VSTD::move_backward(__lb, __le, __r);
        __n -= __bs;
        __l -= __bs - 1;
    }
    return __r;
}

template <class _V1, class _P1, class _R1, class _M1, class _D1, _D1 _B1,
          class _V2, class _P2, class _R2, class _M2, class _D2, _D2 _B2>
_LIBCPP_HIDE_FROM_ABI __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>
move_backward(__deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __f,
              __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
              __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r)
{
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
    typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        --__l;
        pointer __lb = *__l.__m_iter_;
        pointer __le = __l.__ptr_ + 1;
        difference_type __bs = __le - __lb;
        if (__bs > __n)
        {
            __bs = __n;
            __lb = __le - __bs;
        }
        __r = _VSTD::move_backward(__lb, __le, __r);
        __n -= __bs;
        __l -= __bs - 1;
    }
    return __r;
}

template <class _Tp, class _Allocator /*= allocator<_Tp>*/>
class _LIBCPP_TEMPLATE_VIS deque
{
public:
    // types:

  using value_type = _Tp;

  static_assert((is_same<typename _Allocator::value_type, value_type>::value),
                "Allocator::value_type must be same type as value_type");

  using allocator_type = _Allocator;
  using __alloc_traits = allocator_traits<allocator_type>;

  using size_type       = typename __alloc_traits::size_type;
  using difference_type = typename __alloc_traits::difference_type;

  using pointer       = typename __alloc_traits::pointer;
  using const_pointer = typename __alloc_traits::const_pointer;

  using __pointer_allocator       = __rebind_alloc<__alloc_traits, pointer>;
  using __const_pointer_allocator = __rebind_alloc<__alloc_traits, const_pointer>;
  using __map                     = __split_buffer<pointer, __pointer_allocator>;
  using __map_alloc_traits        = allocator_traits<__pointer_allocator>;
  using __map_pointer             = typename __map_alloc_traits::pointer;
  using __map_const_pointer       = typename allocator_traits<__const_pointer_allocator>::const_pointer;

  using reference       = value_type&;
  using const_reference = const value_type&;

  using iterator = __deque_iterator<value_type, pointer, reference, __map_pointer, difference_type>;
  using const_iterator =
      __deque_iterator<value_type, const_pointer, const_reference, __map_const_pointer, difference_type>;
  using reverse_iterator       = std::reverse_iterator<iterator>;
  using const_reverse_iterator = std::reverse_iterator<const_iterator>;

  static_assert(is_same<allocator_type, __rebind_alloc<__alloc_traits, value_type> >::value,
                "[allocator.requirements] states that rebinding an allocator to the same type should result in the "
                "original allocator");
  static_assert(is_nothrow_default_constructible<allocator_type>::value ==
                    is_nothrow_default_constructible<__pointer_allocator>::value,
                "rebinding an allocator should not change excpetion guarantees");
  static_assert(is_nothrow_move_constructible<allocator_type>::value ==
                    is_nothrow_move_constructible<typename __map::allocator_type>::value,
                "rebinding an allocator should not change excpetion guarantees");

private:
  struct __deque_block_range {
    explicit _LIBCPP_HIDE_FROM_ABI
    __deque_block_range(pointer __b, pointer __e) _NOEXCEPT : __begin_(__b), __end_(__e) {}
    const pointer __begin_;
    const pointer __end_;
  };

  struct __deque_range {
    iterator __pos_;
    const iterator __end_;

    _LIBCPP_HIDE_FROM_ABI __deque_range(iterator __pos, iterator __e) _NOEXCEPT
      : __pos_(__pos), __end_(__e) {}

    explicit _LIBCPP_HIDE_FROM_ABI operator bool() const _NOEXCEPT {
      return __pos_ != __end_;
    }

    _LIBCPP_HIDE_FROM_ABI __deque_range begin() const {
      return *this;
    }

    _LIBCPP_HIDE_FROM_ABI __deque_range end() const {
      return __deque_range(__end_, __end_);
    }
    _LIBCPP_HIDE_FROM_ABI __deque_block_range operator*() const _NOEXCEPT {
        if (__pos_.__m_iter_ == __end_.__m_iter_) {
        return __deque_block_range(__pos_.__ptr_, __end_.__ptr_);
      }
      return __deque_block_range(__pos_.__ptr_, *__pos_.__m_iter_ + __block_size);
    }

    _LIBCPP_HIDE_FROM_ABI __deque_range& operator++() _NOEXCEPT {
      if (__pos_.__m_iter_ == __end_.__m_iter_) {
        __pos_ = __end_;
      } else {
        ++__pos_.__m_iter_;
        __pos_.__ptr_ = *__pos_.__m_iter_;
      }
      return *this;
    }


    _LIBCPP_HIDE_FROM_ABI friend bool operator==(__deque_range const& __lhs, __deque_range const& __rhs) {
      return __lhs.__pos_ == __rhs.__pos_;
    }
    _LIBCPP_HIDE_FROM_ABI friend bool operator!=(__deque_range const& __lhs, __deque_range const& __rhs) {
      return !(__lhs == __rhs);
    }
  };

  struct _ConstructTransaction {
    _LIBCPP_HIDE_FROM_ABI _ConstructTransaction(deque* __db, __deque_block_range& __r)
      : __pos_(__r.__begin_), __end_(__r.__end_), __begin_(__r.__begin_), __base_(__db) {}


    _LIBCPP_HIDE_FROM_ABI ~_ConstructTransaction() {
      __base_->__size() += (__pos_ - __begin_);
    }

    pointer __pos_;
    const pointer __end_;
  private:
    const pointer __begin_;
    deque* const __base_;
  };

  static const difference_type __block_size;

  __map __map_;
  size_type __start_;
  __compressed_pair<size_type, allocator_type> __size_;

public:

    // construct/copy/destroy:
    _LIBCPP_HIDE_FROM_ABI
    deque() _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value)
        : __start_(0), __size_(0, __default_init_tag()) {}

    _LIBCPP_HIDE_FROM_ABI ~deque() {
      clear();
      typename __map::iterator __i = __map_.begin();
      typename __map::iterator __e = __map_.end();
      for (; __i != __e; ++__i)
          __alloc_traits::deallocate(__alloc(), *__i, __block_size);
    }

    _LIBCPP_HIDE_FROM_ABI explicit deque(const allocator_type& __a)
        : __map_(__pointer_allocator(__a)), __start_(0), __size_(0, __a) {}

    explicit _LIBCPP_HIDE_FROM_ABI deque(size_type __n);
#if _LIBCPP_STD_VER > 11
    explicit _LIBCPP_HIDE_FROM_ABI deque(size_type __n, const _Allocator& __a);
#endif
    _LIBCPP_HIDE_FROM_ABI deque(size_type __n, const value_type& __v);

    template <class = __enable_if_t<__is_allocator<_Allocator>::value> >
    _LIBCPP_HIDE_FROM_ABI deque(size_type __n, const value_type& __v, const allocator_type& __a)
        : __map_(__pointer_allocator(__a)), __start_(0), __size_(0, __a)
    {
        if (__n > 0)
            __append(__n, __v);
    }

    template <class _InputIter>
    _LIBCPP_HIDE_FROM_ABI deque(_InputIter __f, _InputIter __l,
              typename enable_if<__is_cpp17_input_iterator<_InputIter>::value>::type* = 0);
    template <class _InputIter>
    _LIBCPP_HIDE_FROM_ABI deque(_InputIter __f, _InputIter __l, const allocator_type& __a,
              typename enable_if<__is_cpp17_input_iterator<_InputIter>::value>::type* = 0);
    _LIBCPP_HIDE_FROM_ABI deque(const deque& __c);
    _LIBCPP_HIDE_FROM_ABI deque(const deque& __c, const __type_identity_t<allocator_type>& __a);

    _LIBCPP_HIDE_FROM_ABI deque& operator=(const deque& __c);

#ifndef _LIBCPP_CXX03_LANG
    _LIBCPP_HIDE_FROM_ABI deque(initializer_list<value_type> __il);
    _LIBCPP_HIDE_FROM_ABI deque(initializer_list<value_type> __il, const allocator_type& __a);

    _LIBCPP_HIDE_FROM_ABI
    deque& operator=(initializer_list<value_type> __il) {assign(__il); return *this;}

    _LIBCPP_HIDE_FROM_ABI
    deque(deque&& __c) _NOEXCEPT_(is_nothrow_move_constructible<allocator_type>::value);
    _LIBCPP_HIDE_FROM_ABI
    deque(deque&& __c, const __type_identity_t<allocator_type>& __a);
    _LIBCPP_HIDE_FROM_ABI
    deque& operator=(deque&& __c)
        _NOEXCEPT_(__alloc_traits::propagate_on_container_move_assignment::value &&
                   is_nothrow_move_assignable<allocator_type>::value);

    _LIBCPP_HIDE_FROM_ABI
    void assign(initializer_list<value_type> __il) {assign(__il.begin(), __il.end());}
#endif // _LIBCPP_CXX03_LANG

    template <class _InputIter>
    _LIBCPP_HIDE_FROM_ABI void assign(_InputIter __f, _InputIter __l,
                    typename enable_if<__is_cpp17_input_iterator<_InputIter>::value &&
                                      !__is_cpp17_random_access_iterator<_InputIter>::value>::type* = 0);
    template <class _RAIter>
    _LIBCPP_HIDE_FROM_ABI void assign(_RAIter __f, _RAIter __l,
                    typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type* = 0);
    _LIBCPP_HIDE_FROM_ABI void assign(size_type __n, const value_type& __v);

    _LIBCPP_HIDE_FROM_ABI
    allocator_type get_allocator() const _NOEXCEPT;
  _LIBCPP_HIDE_FROM_ABI allocator_type& __alloc() _NOEXCEPT { return __size_.second(); }
  _LIBCPP_HIDE_FROM_ABI const allocator_type& __alloc() const _NOEXCEPT { return __size_.second(); }

  // iterators:

  _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT {
      __map_pointer __mp = __map_.begin() + __start_ / __block_size;
      return iterator(__mp, __map_.empty() ? 0 : *__mp + __start_ % __block_size);
  }

  _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT {
      __map_const_pointer __mp =
          static_cast<__map_const_pointer>(__map_.begin() + __start_ / __block_size);
      return const_iterator(__mp, __map_.empty() ? 0 : *__mp + __start_ % __block_size);
  }

  _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT {
      size_type __p      = size() + __start_;
      __map_pointer __mp = __map_.begin() + __p / __block_size;
      return iterator(__mp, __map_.empty() ? 0 : *__mp + __p % __block_size);
  }

  _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT {
      size_type __p            = size() + __start_;
      __map_const_pointer __mp = static_cast<__map_const_pointer>(__map_.begin() + __p / __block_size);
      return const_iterator(__mp, __map_.empty() ? 0 : *__mp + __p % __block_size);
  }

    _LIBCPP_HIDE_FROM_ABI
    reverse_iterator       rbegin() _NOEXCEPT
        {return       reverse_iterator(end());}
    _LIBCPP_HIDE_FROM_ABI
    const_reverse_iterator rbegin() const _NOEXCEPT
        {return const_reverse_iterator(end());}
    _LIBCPP_HIDE_FROM_ABI
    reverse_iterator       rend() _NOEXCEPT
        {return       reverse_iterator(begin());}
    _LIBCPP_HIDE_FROM_ABI
    const_reverse_iterator rend()   const _NOEXCEPT
        {return const_reverse_iterator(begin());}

    _LIBCPP_HIDE_FROM_ABI
    const_iterator         cbegin()  const _NOEXCEPT
        {return begin();}
    _LIBCPP_HIDE_FROM_ABI
    const_iterator         cend()    const _NOEXCEPT
        {return end();}
    _LIBCPP_HIDE_FROM_ABI
    const_reverse_iterator crbegin() const _NOEXCEPT
        {return const_reverse_iterator(end());}
    _LIBCPP_HIDE_FROM_ABI
    const_reverse_iterator crend()   const _NOEXCEPT
        {return const_reverse_iterator(begin());}

    // capacity:
    _LIBCPP_HIDE_FROM_ABI
    size_type size() const _NOEXCEPT {return __size();}

  _LIBCPP_HIDE_FROM_ABI size_type& __size() _NOEXCEPT { return __size_.first(); }
  _LIBCPP_HIDE_FROM_ABI const size_type& __size() const _NOEXCEPT { return __size_.first(); }

    _LIBCPP_HIDE_FROM_ABI
    size_type max_size() const _NOEXCEPT
        {return _VSTD::min<size_type>(
            __alloc_traits::max_size(__alloc()),
            numeric_limits<difference_type>::max());}
    _LIBCPP_HIDE_FROM_ABI void resize(size_type __n);
    _LIBCPP_HIDE_FROM_ABI void resize(size_type __n, const value_type& __v);
    _LIBCPP_HIDE_FROM_ABI void shrink_to_fit() _NOEXCEPT;
    _LIBCPP_NODISCARD_AFTER_CXX17 _LIBCPP_HIDE_FROM_ABI
    bool empty() const _NOEXCEPT {return size() == 0;}

    // element access:
    _LIBCPP_HIDE_FROM_ABI
    reference operator[](size_type __i) _NOEXCEPT;
    _LIBCPP_HIDE_FROM_ABI
    const_reference operator[](size_type __i) const _NOEXCEPT;
    _LIBCPP_HIDE_FROM_ABI
    reference at(size_type __i);
    _LIBCPP_HIDE_FROM_ABI
    const_reference at(size_type __i) const;
    _LIBCPP_HIDE_FROM_ABI
    reference front() _NOEXCEPT;
    _LIBCPP_HIDE_FROM_ABI
    const_reference front() const _NOEXCEPT;
    _LIBCPP_HIDE_FROM_ABI
    reference back() _NOEXCEPT;
    _LIBCPP_HIDE_FROM_ABI
    const_reference back() const _NOEXCEPT;

    // 23.2.2.3 modifiers:
    _LIBCPP_HIDE_FROM_ABI void push_front(const value_type& __v);
    _LIBCPP_HIDE_FROM_ABI void push_back(const value_type& __v);
#ifndef _LIBCPP_CXX03_LANG
#if _LIBCPP_STD_VER > 14
    template <class... _Args> _LIBCPP_HIDE_FROM_ABI reference emplace_front(_Args&&... __args);
    template <class... _Args> _LIBCPP_HIDE_FROM_ABI reference emplace_back (_Args&&... __args);
#else
    template <class... _Args> _LIBCPP_HIDE_FROM_ABI void      emplace_front(_Args&&... __args);
    template <class... _Args> _LIBCPP_HIDE_FROM_ABI void      emplace_back (_Args&&... __args);
#endif
    template <class... _Args> _LIBCPP_HIDE_FROM_ABI iterator emplace(const_iterator __p, _Args&&... __args);

    _LIBCPP_HIDE_FROM_ABI void push_front(value_type&& __v);
    _LIBCPP_HIDE_FROM_ABI void push_back(value_type&& __v);
    _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __p, value_type&& __v);

    _LIBCPP_HIDE_FROM_ABI
    iterator insert(const_iterator __p, initializer_list<value_type> __il)
        {return insert(__p, __il.begin(), __il.end());}
#endif // _LIBCPP_CXX03_LANG
    _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __p, const value_type& __v);
    _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __p, size_type __n, const value_type& __v);
    template <class _InputIter>
    _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __p, _InputIter __f, _InputIter __l,
                         typename enable_if<__is_exactly_cpp17_input_iterator<_InputIter>::value>::type* = 0);
    template <class _ForwardIterator>
    _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __p, _ForwardIterator __f, _ForwardIterator __l,
                        typename enable_if<__is_exactly_cpp17_forward_iterator<_ForwardIterator>::value>::type* = 0);
    template <class _BiIter>
    _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __p, _BiIter __f, _BiIter __l,
                         typename enable_if<__is_cpp17_bidirectional_iterator<_BiIter>::value>::type* = 0);

    _LIBCPP_HIDE_FROM_ABI void pop_front();
    _LIBCPP_HIDE_FROM_ABI void pop_back();
    _LIBCPP_HIDE_FROM_ABI iterator erase(const_iterator __p);
    _LIBCPP_HIDE_FROM_ABI iterator erase(const_iterator __f, const_iterator __l);

    _LIBCPP_HIDE_FROM_ABI
    void swap(deque& __c)
#if _LIBCPP_STD_VER >= 14
        _NOEXCEPT;
#else
        _NOEXCEPT_(!__alloc_traits::propagate_on_container_swap::value ||
                   __is_nothrow_swappable<allocator_type>::value);
#endif
    _LIBCPP_HIDE_FROM_ABI
    void clear() _NOEXCEPT;

    _LIBCPP_HIDE_FROM_ABI
    bool __invariants() const {
        if (!__map_.__invariants())
            return false;
        if (__map_.size() >= size_type(-1) / __block_size)
            return false;
        for (typename __map::const_iterator __i = __map_.begin(), __e = __map_.end();
            __i != __e; ++__i)
            if (*__i == nullptr)
                return false;
        if (__map_.size() != 0)
        {
            if (size() >= __map_.size() * __block_size)
                return false;
            if (__start_ >= __map_.size() * __block_size - size())
                return false;
        }
        else
        {
            if (size() != 0)
                return false;
            if (__start_ != 0)
                return false;
        }
        return true;
    }

    _LIBCPP_HIDE_FROM_ABI
    void __move_assign_alloc(deque& __c)
        _NOEXCEPT_(!__alloc_traits::propagate_on_container_move_assignment::value ||
                   is_nothrow_move_assignable<allocator_type>::value)
        {__move_assign_alloc(__c, integral_constant<bool,
                      __alloc_traits::propagate_on_container_move_assignment::value>());}

    _LIBCPP_HIDE_FROM_ABI
    void __move_assign_alloc(deque& __c, true_type)
        _NOEXCEPT_(is_nothrow_move_assignable<allocator_type>::value)
        {
            __alloc() = _VSTD::move(__c.__alloc());
        }

    _LIBCPP_HIDE_FROM_ABI
    void __move_assign_alloc(deque&, false_type) _NOEXCEPT
        {}

    _LIBCPP_HIDE_FROM_ABI
    void __move_assign(deque& __c)
        _NOEXCEPT_(__alloc_traits::propagate_on_container_move_assignment::value &&
                   is_nothrow_move_assignable<allocator_type>::value)
    {
        __map_ = _VSTD::move(__c.__map_);
        __start_ = __c.__start_;
        __size() = __c.size();
        __move_assign_alloc(__c);
        __c.__start_ = __c.__size() = 0;
    }

    _LIBCPP_HIDE_FROM_ABI
    static size_type __recommend_blocks(size_type __n)
    {
        return __n / __block_size + (__n % __block_size != 0);
    }
    _LIBCPP_HIDE_FROM_ABI
    size_type __capacity() const
    {
        return __map_.size() == 0 ? 0 : __map_.size() * __block_size - 1;
    }
    _LIBCPP_HIDE_FROM_ABI
    size_type __block_count() const
    {
        return __map_.size();
    }

    _LIBCPP_HIDE_FROM_ABI
    size_type __front_spare() const
    {
        return __start_;
    }
    _LIBCPP_HIDE_FROM_ABI
    size_type __front_spare_blocks() const {
      return __front_spare() / __block_size;
    }
    _LIBCPP_HIDE_FROM_ABI
    size_type __back_spare() const
    {
        return __capacity() - (__start_ + size());
    }
    _LIBCPP_HIDE_FROM_ABI
    size_type __back_spare_blocks() const {
      return __back_spare() / __block_size;
    }

 private:
    _LIBCPP_HIDE_FROM_ABI
    bool __maybe_remove_front_spare(bool __keep_one = true) {
      if (__front_spare_blocks() >= 2 || (!__keep_one && __front_spare_blocks())) {
        __alloc_traits::deallocate(__alloc(), __map_.front(),
                                   __block_size);
        __map_.pop_front();
        __start_ -= __block_size;
        return true;
      }
      return false;
    }

    _LIBCPP_HIDE_FROM_ABI
    bool __maybe_remove_back_spare(bool __keep_one = true) {
      if (__back_spare_blocks() >= 2 || (!__keep_one && __back_spare_blocks())) {
        __alloc_traits::deallocate(__alloc(), __map_.back(),
                                   __block_size);
        __map_.pop_back();
        return true;
      }
      return false;
    }

    template <class _InpIter>
    _LIBCPP_HIDE_FROM_ABI void __append(_InpIter __f, _InpIter __l,
                 typename enable_if<__is_exactly_cpp17_input_iterator<_InpIter>::value>::type* = 0);
    template <class _ForIter>
    _LIBCPP_HIDE_FROM_ABI void __append(_ForIter __f, _ForIter __l,
                      typename enable_if<__is_cpp17_forward_iterator<_ForIter>::value>::type* = 0);
    _LIBCPP_HIDE_FROM_ABI void __append(size_type __n);
    _LIBCPP_HIDE_FROM_ABI void __append(size_type __n, const value_type& __v);
    _LIBCPP_HIDE_FROM_ABI void __erase_to_end(const_iterator __f);
    _LIBCPP_HIDE_FROM_ABI void __add_front_capacity();
    _LIBCPP_HIDE_FROM_ABI void __add_front_capacity(size_type __n);
    _LIBCPP_HIDE_FROM_ABI void __add_back_capacity();
    _LIBCPP_HIDE_FROM_ABI void __add_back_capacity(size_type __n);
    _LIBCPP_HIDE_FROM_ABI iterator __move_and_check(iterator __f, iterator __l, iterator __r,
                              const_pointer& __vt);
    _LIBCPP_HIDE_FROM_ABI iterator __move_backward_and_check(iterator __f, iterator __l, iterator __r,
                                       const_pointer& __vt);
    _LIBCPP_HIDE_FROM_ABI void __move_construct_and_check(iterator __f, iterator __l,
                                    iterator __r, const_pointer& __vt);
    _LIBCPP_HIDE_FROM_ABI void __move_construct_backward_and_check(iterator __f, iterator __l,
                                             iterator __r, const_pointer& __vt);

    _LIBCPP_HIDE_FROM_ABI
    void __copy_assign_alloc(const deque& __c)
        {__copy_assign_alloc(__c, integral_constant<bool,
                      __alloc_traits::propagate_on_container_copy_assignment::value>());}

    _LIBCPP_HIDE_FROM_ABI
    void __copy_assign_alloc(const deque& __c, true_type)
        {
            if (__alloc() != __c.__alloc())
            {
                clear();
                shrink_to_fit();
            }
            __alloc() = __c.__alloc();
            __map_.__alloc() = __c.__map_.__alloc();
        }

    _LIBCPP_HIDE_FROM_ABI
    void __copy_assign_alloc(const deque&, false_type)
        {}

    _LIBCPP_HIDE_FROM_ABI void __move_assign(deque& __c, true_type)
        _NOEXCEPT_(is_nothrow_move_assignable<allocator_type>::value);
    _LIBCPP_HIDE_FROM_ABI void __move_assign(deque& __c, false_type);
};

template <class _Tp, class _Alloc>
_LIBCPP_CONSTEXPR const typename allocator_traits<_Alloc>::difference_type deque<_Tp, _Alloc>::__block_size =
    __deque_block_size<value_type, difference_type>::value;

#if _LIBCPP_STD_VER >= 17
template<class _InputIterator,
         class _Alloc = allocator<__iter_value_type<_InputIterator>>,
         class = enable_if_t<__is_cpp17_input_iterator<_InputIterator>::value>,
         class = enable_if_t<__is_allocator<_Alloc>::value>
         >
deque(_InputIterator, _InputIterator)
  -> deque<__iter_value_type<_InputIterator>, _Alloc>;

template<class _InputIterator,
         class _Alloc,
         class = enable_if_t<__is_cpp17_input_iterator<_InputIterator>::value>,
         class = enable_if_t<__is_allocator<_Alloc>::value>
         >
deque(_InputIterator, _InputIterator, _Alloc)
  -> deque<__iter_value_type<_InputIterator>, _Alloc>;
#endif

template <class _Tp, class _Allocator>
deque<_Tp, _Allocator>::deque(size_type __n)
    : __start_(0), __size_(0, __default_init_tag())
{
    if (__n > 0)
        __append(__n);
}

#if _LIBCPP_STD_VER > 11
template <class _Tp, class _Allocator>
deque<_Tp, _Allocator>::deque(size_type __n, const _Allocator& __a)
    : __map_(__pointer_allocator(__a)), __start_(0), __size_(0, __a)
{
    if (__n > 0)
        __append(__n);
}
#endif

template <class _Tp, class _Allocator>
deque<_Tp, _Allocator>::deque(size_type __n, const value_type& __v)
    : __start_(0), __size_(0, __default_init_tag())
{
    if (__n > 0)
        __append(__n, __v);
}

template <class _Tp, class _Allocator>
template <class _InputIter>
deque<_Tp, _Allocator>::deque(_InputIter __f, _InputIter __l,
              typename enable_if<__is_cpp17_input_iterator<_InputIter>::value>::type*)
    : __start_(0), __size_(0, __default_init_tag())
{
    __append(__f, __l);
}

template <class _Tp, class _Allocator>
template <class _InputIter>
deque<_Tp, _Allocator>::deque(_InputIter __f, _InputIter __l, const allocator_type& __a,
              typename enable_if<__is_cpp17_input_iterator<_InputIter>::value>::type*)
    : __map_(__pointer_allocator(__a)), __start_(0), __size_(0, __a)
{
    __append(__f, __l);
}

template <class _Tp, class _Allocator>
deque<_Tp, _Allocator>::deque(const deque& __c)
    : __map_(__pointer_allocator(__alloc_traits::select_on_container_copy_construction(__c.__alloc()))),
      __start_(0),
      __size_(0, __map_.__alloc())
{
    __append(__c.begin(), __c.end());
}

template <class _Tp, class _Allocator>
deque<_Tp, _Allocator>::deque(const deque& __c, const __type_identity_t<allocator_type>& __a)
    : __map_(__pointer_allocator(__a)), __start_(0), __size_(0, __a)
{
    __append(__c.begin(), __c.end());
}

template <class _Tp, class _Allocator>
deque<_Tp, _Allocator>&
deque<_Tp, _Allocator>::operator=(const deque& __c)
{
    if (this != _VSTD::addressof(__c))
    {
        __copy_assign_alloc(__c);
        assign(__c.begin(), __c.end());
    }
    return *this;
}

#ifndef _LIBCPP_CXX03_LANG

template <class _Tp, class _Allocator>
deque<_Tp, _Allocator>::deque(initializer_list<value_type> __il)
    : __start_(0), __size_(0, __default_init_tag())
{
    __append(__il.begin(), __il.end());
}

template <class _Tp, class _Allocator>
deque<_Tp, _Allocator>::deque(initializer_list<value_type> __il, const allocator_type& __a)
    : __map_(__pointer_allocator(__a)), __start_(0), __size_(0, __a)
{
    __append(__il.begin(), __il.end());
}

template <class _Tp, class _Allocator>
inline
deque<_Tp, _Allocator>::deque(deque&& __c)
    _NOEXCEPT_(is_nothrow_move_constructible<allocator_type>::value)
    : __map_(std::move(__c.__map_)), __start_(std::move(__c.__start_)), __size_(std::move(__c.__size_))
{
  __c.__start_ = 0;
  __c.__size() = 0;
}

template <class _Tp, class _Allocator>
inline
deque<_Tp, _Allocator>::deque(deque&& __c, const __type_identity_t<allocator_type>& __a)
    : __map_(std::move(__c.__map_), __pointer_allocator(__a)),
      __start_(std::move(__c.__start_)),
      __size_(std::move(__c.__size()), __a)
{
    if (__a == __c.__alloc())
    {
        __c.__start_ = 0;
        __c.__size() = 0;
    }
    else
    {
        __map_.clear();
        __start_ = 0;
        __size() = 0;
        typedef move_iterator<iterator> _Ip;
        assign(_Ip(__c.begin()), _Ip(__c.end()));
    }
}

template <class _Tp, class _Allocator>
inline
deque<_Tp, _Allocator>&
deque<_Tp, _Allocator>::operator=(deque&& __c)
        _NOEXCEPT_(__alloc_traits::propagate_on_container_move_assignment::value &&
                   is_nothrow_move_assignable<allocator_type>::value)
{
    __move_assign(__c, integral_constant<bool,
          __alloc_traits::propagate_on_container_move_assignment::value>());
    return *this;
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::__move_assign(deque& __c, false_type)
{
    if (__alloc() != __c.__alloc())
    {
        typedef move_iterator<iterator> _Ip;
        assign(_Ip(__c.begin()), _Ip(__c.end()));
    }
    else
        __move_assign(__c, true_type());
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::__move_assign(deque& __c, true_type)
    _NOEXCEPT_(is_nothrow_move_assignable<allocator_type>::value)
{
    clear();
    shrink_to_fit();
    __move_assign(__c);
}

#endif // _LIBCPP_CXX03_LANG

template <class _Tp, class _Allocator>
template <class _InputIter>
void
deque<_Tp, _Allocator>::assign(_InputIter __f, _InputIter __l,
                               typename enable_if<__is_cpp17_input_iterator<_InputIter>::value &&
                                                 !__is_cpp17_random_access_iterator<_InputIter>::value>::type*)
{
    iterator __i = begin();
    iterator __e = end();
    for (; __f != __l && __i != __e; ++__f, (void) ++__i)
        *__i = *__f;
    if (__f != __l)
        __append(__f, __l);
    else
        __erase_to_end(__i);
}

template <class _Tp, class _Allocator>
template <class _RAIter>
void
deque<_Tp, _Allocator>::assign(_RAIter __f, _RAIter __l,
                               typename enable_if<__is_cpp17_random_access_iterator<_RAIter>::value>::type*)
{
    if (static_cast<size_type>(__l - __f) > size())
    {
        _RAIter __m = __f + size();
        _VSTD::copy(__f, __m, begin());
        __append(__m, __l);
    }
    else
        __erase_to_end(_VSTD::copy(__f, __l, begin()));
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::assign(size_type __n, const value_type& __v)
{
    if (__n > size())
    {
        _VSTD::fill_n(begin(), size(), __v);
        __n -= size();
        __append(__n, __v);
    }
    else
        __erase_to_end(_VSTD::fill_n(begin(), __n, __v));
}

template <class _Tp, class _Allocator>
inline
_Allocator
deque<_Tp, _Allocator>::get_allocator() const _NOEXCEPT
{
    return __alloc();
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::resize(size_type __n)
{
    if (__n > size())
        __append(__n - size());
    else if (__n < size())
        __erase_to_end(begin() + __n);
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::resize(size_type __n, const value_type& __v)
{
    if (__n > size())
        __append(__n - size(), __v);
    else if (__n < size())
        __erase_to_end(begin() + __n);
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::shrink_to_fit() _NOEXCEPT
{
    allocator_type& __a = __alloc();
    if (empty())
    {
        while (__map_.size() > 0)
        {
            __alloc_traits::deallocate(__a, __map_.back(), __block_size);
            __map_.pop_back();
        }
        __start_ = 0;
    }
    else
    {
      __maybe_remove_front_spare(/*__keep_one=*/false);
      __maybe_remove_back_spare(/*__keep_one=*/false);
    }
    __map_.shrink_to_fit();
}

template <class _Tp, class _Allocator>
inline
typename deque<_Tp, _Allocator>::reference
deque<_Tp, _Allocator>::operator[](size_type __i) _NOEXCEPT
{
    size_type __p = __start_ + __i;
    return *(*(__map_.begin() + __p / __block_size) + __p % __block_size);
}

template <class _Tp, class _Allocator>
inline
typename deque<_Tp, _Allocator>::const_reference
deque<_Tp, _Allocator>::operator[](size_type __i) const _NOEXCEPT
{
    size_type __p = __start_ + __i;
    return *(*(__map_.begin() + __p / __block_size) + __p % __block_size);
}

template <class _Tp, class _Allocator>
inline
typename deque<_Tp, _Allocator>::reference
deque<_Tp, _Allocator>::at(size_type __i)
{
    if (__i >= size())
        _VSTD::__throw_out_of_range("deque");
    size_type __p = __start_ + __i;
    return *(*(__map_.begin() + __p / __block_size) + __p % __block_size);
}

template <class _Tp, class _Allocator>
inline
typename deque<_Tp, _Allocator>::const_reference
deque<_Tp, _Allocator>::at(size_type __i) const
{
    if (__i >= size())
        _VSTD::__throw_out_of_range("deque");
    size_type __p = __start_ + __i;
    return *(*(__map_.begin() + __p / __block_size) + __p % __block_size);
}

template <class _Tp, class _Allocator>
inline
typename deque<_Tp, _Allocator>::reference
deque<_Tp, _Allocator>::front() _NOEXCEPT
{
    return *(*(__map_.begin() + __start_ / __block_size)
                                    + __start_ % __block_size);
}

template <class _Tp, class _Allocator>
inline
typename deque<_Tp, _Allocator>::const_reference
deque<_Tp, _Allocator>::front() const _NOEXCEPT
{
    return *(*(__map_.begin() + __start_ / __block_size)
                                      + __start_ % __block_size);
}

template <class _Tp, class _Allocator>
inline
typename deque<_Tp, _Allocator>::reference
deque<_Tp, _Allocator>::back() _NOEXCEPT
{
    size_type __p = size() + __start_ - 1;
    return *(*(__map_.begin() + __p / __block_size) + __p % __block_size);
}

template <class _Tp, class _Allocator>
inline
typename deque<_Tp, _Allocator>::const_reference
deque<_Tp, _Allocator>::back() const _NOEXCEPT
{
    size_type __p = size() + __start_ - 1;
    return *(*(__map_.begin() + __p / __block_size) + __p % __block_size);
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::push_back(const value_type& __v)
{
    allocator_type& __a = __alloc();
    if (__back_spare() == 0)
        __add_back_capacity();
    // __back_spare() >= 1
    __alloc_traits::construct(__a, _VSTD::addressof(*end()), __v);
    ++__size();
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::push_front(const value_type& __v)
{
    allocator_type& __a = __alloc();
    if (__front_spare() == 0)
        __add_front_capacity();
    // __front_spare() >= 1
    __alloc_traits::construct(__a, _VSTD::addressof(*--begin()), __v);
    --__start_;
    ++__size();
}

#ifndef _LIBCPP_CXX03_LANG
template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::push_back(value_type&& __v)
{
    allocator_type& __a = __alloc();
    if (__back_spare() == 0)
        __add_back_capacity();
    // __back_spare() >= 1
    __alloc_traits::construct(__a, _VSTD::addressof(*end()), _VSTD::move(__v));
    ++__size();
}

template <class _Tp, class _Allocator>
template <class... _Args>
#if _LIBCPP_STD_VER > 14
typename deque<_Tp, _Allocator>::reference
#else
void
#endif
deque<_Tp, _Allocator>::emplace_back(_Args&&... __args)
{
    allocator_type& __a = __alloc();
    if (__back_spare() == 0)
        __add_back_capacity();
    // __back_spare() >= 1
    __alloc_traits::construct(__a, _VSTD::addressof(*end()),
                              _VSTD::forward<_Args>(__args)...);
    ++__size();
#if _LIBCPP_STD_VER > 14
    return *--end();
#endif
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::push_front(value_type&& __v)
{
    allocator_type& __a = __alloc();
    if (__front_spare() == 0)
        __add_front_capacity();
    // __front_spare() >= 1
    __alloc_traits::construct(__a, _VSTD::addressof(*--begin()), _VSTD::move(__v));
    --__start_;
    ++__size();
}


template <class _Tp, class _Allocator>
template <class... _Args>
#if _LIBCPP_STD_VER > 14
typename deque<_Tp, _Allocator>::reference
#else
void
#endif
deque<_Tp, _Allocator>::emplace_front(_Args&&... __args)
{
    allocator_type& __a = __alloc();
    if (__front_spare() == 0)
        __add_front_capacity();
    // __front_spare() >= 1
    __alloc_traits::construct(__a, _VSTD::addressof(*--begin()), _VSTD::forward<_Args>(__args)...);
    --__start_;
    ++__size();
#if _LIBCPP_STD_VER > 14
    return *begin();
#endif
}

template <class _Tp, class _Allocator>
typename deque<_Tp, _Allocator>::iterator
deque<_Tp, _Allocator>::insert(const_iterator __p, value_type&& __v)
{
    size_type __pos = __p - begin();
    size_type __to_end = size() - __pos;
    allocator_type& __a = __alloc();
    if (__pos < __to_end)
    {   // insert by shifting things backward
        if (__front_spare() == 0)
            __add_front_capacity();
        // __front_spare() >= 1
        if (__pos == 0)
        {
            __alloc_traits::construct(__a, _VSTD::addressof(*--begin()), _VSTD::move(__v));
            --__start_;
            ++__size();
        }
        else
        {
            iterator __b = begin();
            iterator __bm1 = _VSTD::prev(__b);
            __alloc_traits::construct(__a, _VSTD::addressof(*__bm1), _VSTD::move(*__b));
            --__start_;
            ++__size();
            if (__pos > 1)
                __b = _VSTD::move(_VSTD::next(__b), __b + __pos, __b);
            *__b = _VSTD::move(__v);
        }
    }
    else
    {   // insert by shifting things forward
        if (__back_spare() == 0)
            __add_back_capacity();
        // __back_capacity >= 1
        size_type __de = size() - __pos;
        if (__de == 0)
        {
            __alloc_traits::construct(__a, _VSTD::addressof(*end()), _VSTD::move(__v));
            ++__size();
        }
        else
        {
            iterator __e = end();
            iterator __em1 = _VSTD::prev(__e);
            __alloc_traits::construct(__a, _VSTD::addressof(*__e), _VSTD::move(*__em1));
            ++__size();
            if (__de > 1)
                __e = _VSTD::move_backward(__e - __de, __em1, __e);
            *--__e = _VSTD::move(__v);
        }
    }
    return begin() + __pos;
}

template <class _Tp, class _Allocator>
template <class... _Args>
typename deque<_Tp, _Allocator>::iterator
deque<_Tp, _Allocator>::emplace(const_iterator __p, _Args&&... __args)
{
    size_type __pos = __p - begin();
    size_type __to_end = size() - __pos;
    allocator_type& __a = __alloc();
    if (__pos < __to_end)
    {   // insert by shifting things backward
        if (__front_spare() == 0)
            __add_front_capacity();
        // __front_spare() >= 1
        if (__pos == 0)
        {
            __alloc_traits::construct(__a, _VSTD::addressof(*--begin()), _VSTD::forward<_Args>(__args)...);
            --__start_;
            ++__size();
        }
        else
        {
            __temp_value<value_type, _Allocator> __tmp(__alloc(), _VSTD::forward<_Args>(__args)...);
            iterator __b = begin();
            iterator __bm1 = _VSTD::prev(__b);
            __alloc_traits::construct(__a, _VSTD::addressof(*__bm1), _VSTD::move(*__b));
            --__start_;
            ++__size();
            if (__pos > 1)
                __b = _VSTD::move(_VSTD::next(__b), __b + __pos, __b);
            *__b = _VSTD::move(__tmp.get());
        }
    }
    else
    {   // insert by shifting things forward
        if (__back_spare() == 0)
            __add_back_capacity();
        // __back_capacity >= 1
        size_type __de = size() - __pos;
        if (__de == 0)
        {
            __alloc_traits::construct(__a, _VSTD::addressof(*end()), _VSTD::forward<_Args>(__args)...);
            ++__size();
        }
        else
        {
            __temp_value<value_type, _Allocator> __tmp(__alloc(), _VSTD::forward<_Args>(__args)...);
            iterator __e = end();
            iterator __em1 = _VSTD::prev(__e);
            __alloc_traits::construct(__a, _VSTD::addressof(*__e), _VSTD::move(*__em1));
            ++__size();
            if (__de > 1)
                __e = _VSTD::move_backward(__e - __de, __em1, __e);
            *--__e = _VSTD::move(__tmp.get());
        }
    }
    return begin() + __pos;
}

#endif // _LIBCPP_CXX03_LANG


template <class _Tp, class _Allocator>
typename deque<_Tp, _Allocator>::iterator
deque<_Tp, _Allocator>::insert(const_iterator __p, const value_type& __v)
{
    size_type __pos = __p - begin();
    size_type __to_end = size() - __pos;
    allocator_type& __a = __alloc();
    if (__pos < __to_end)
    {   // insert by shifting things backward
        if (__front_spare() == 0)
            __add_front_capacity();
        // __front_spare() >= 1
        if (__pos == 0)
        {
            __alloc_traits::construct(__a, _VSTD::addressof(*--begin()), __v);
            --__start_;
            ++__size();
        }
        else
        {
            const_pointer __vt = pointer_traits<const_pointer>::pointer_to(__v);
            iterator __b = begin();
            iterator __bm1 = _VSTD::prev(__b);
            if (__vt == pointer_traits<const_pointer>::pointer_to(*__b))
                __vt = pointer_traits<const_pointer>::pointer_to(*__bm1);
            __alloc_traits::construct(__a, _VSTD::addressof(*__bm1), _VSTD::move(*__b));
            --__start_;
            ++__size();
            if (__pos > 1)
                __b = __move_and_check(_VSTD::next(__b), __b + __pos, __b, __vt);
            *__b = *__vt;
        }
    }
    else
    {   // insert by shifting things forward
        if (__back_spare() == 0)
            __add_back_capacity();
        // __back_capacity >= 1
        size_type __de = size() - __pos;
        if (__de == 0)
        {
            __alloc_traits::construct(__a, _VSTD::addressof(*end()), __v);
            ++__size();
        }
        else
        {
            const_pointer __vt = pointer_traits<const_pointer>::pointer_to(__v);
            iterator __e = end();
            iterator __em1 = _VSTD::prev(__e);
            if (__vt == pointer_traits<const_pointer>::pointer_to(*__em1))
                __vt = pointer_traits<const_pointer>::pointer_to(*__e);
            __alloc_traits::construct(__a, _VSTD::addressof(*__e), _VSTD::move(*__em1));
            ++__size();
            if (__de > 1)
                __e = __move_backward_and_check(__e - __de, __em1, __e, __vt);
            *--__e = *__vt;
        }
    }
    return begin() + __pos;
}

template <class _Tp, class _Allocator>
typename deque<_Tp, _Allocator>::iterator
deque<_Tp, _Allocator>::insert(const_iterator __p, size_type __n, const value_type& __v)
{
    size_type __pos = __p - begin();
    size_type __to_end = __size() - __pos;
    allocator_type& __a = __alloc();
    if (__pos < __to_end)
    {   // insert by shifting things backward
        if (__n > __front_spare())
            __add_front_capacity(__n - __front_spare());
        // __n <= __front_spare()
        iterator __old_begin = begin();
        iterator __i = __old_begin;
        if (__n > __pos)
        {
            for (size_type __m = __n - __pos; __m; --__m, --__start_, ++__size())
                __alloc_traits::construct(__a, _VSTD::addressof(*--__i), __v);
            __n = __pos;
        }
        if (__n > 0)
        {
            const_pointer __vt = pointer_traits<const_pointer>::pointer_to(__v);
            iterator __obn = __old_begin + __n;
            __move_construct_backward_and_check(__old_begin, __obn, __i, __vt);
            if (__n < __pos)
                __old_begin = __move_and_check(__obn, __old_begin + __pos, __old_begin, __vt);
            _VSTD::fill_n(__old_begin, __n, *__vt);
        }
    }
    else
    {   // insert by shifting things forward
        size_type __back_capacity = __back_spare();
        if (__n > __back_capacity)
            __add_back_capacity(__n - __back_capacity);
        // __n <= __back_capacity
        iterator __old_end = end();
        iterator __i = __old_end;
        size_type __de = size() - __pos;
        if (__n > __de)
        {
            for (size_type __m = __n - __de; __m; --__m, (void) ++__i, ++__size())
                __alloc_traits::construct(__a, _VSTD::addressof(*__i), __v);
            __n = __de;
        }
        if (__n > 0)
        {
            const_pointer __vt = pointer_traits<const_pointer>::pointer_to(__v);
            iterator __oen = __old_end - __n;
            __move_construct_and_check(__oen, __old_end, __i, __vt);
            if (__n < __de)
                __old_end = __move_backward_and_check(__old_end - __de, __oen, __old_end, __vt);
            _VSTD::fill_n(__old_end - __n, __n, *__vt);
        }
    }
    return begin() + __pos;
}

template <class _Tp, class _Allocator>
template <class _InputIter>
typename deque<_Tp, _Allocator>::iterator
deque<_Tp, _Allocator>::insert(const_iterator __p, _InputIter __f, _InputIter __l,
                               typename enable_if<__is_exactly_cpp17_input_iterator<_InputIter>::value>::type*)
{
    __split_buffer<value_type, allocator_type&> __buf(__alloc());
    __buf.__construct_at_end(__f, __l);
    typedef typename __split_buffer<value_type, allocator_type&>::iterator __bi;
    return insert(__p, move_iterator<__bi>(__buf.begin()), move_iterator<__bi>(__buf.end()));
}

template <class _Tp, class _Allocator>
template <class _ForwardIterator>
typename deque<_Tp, _Allocator>::iterator
deque<_Tp, _Allocator>::insert(const_iterator __p, _ForwardIterator __f, _ForwardIterator __l,
                               typename enable_if<__is_exactly_cpp17_forward_iterator<_ForwardIterator>::value>::type*)
{
    size_type __n = _VSTD::distance(__f, __l);
    __split_buffer<value_type, allocator_type&> __buf(__n, 0, __alloc());
    __buf.__construct_at_end(__f, __l);
    typedef typename __split_buffer<value_type, allocator_type&>::iterator __fwd;
    return insert(__p, move_iterator<__fwd>(__buf.begin()), move_iterator<__fwd>(__buf.end()));
}

template <class _Tp, class _Allocator>
template <class _BiIter>
typename deque<_Tp, _Allocator>::iterator
deque<_Tp, _Allocator>::insert(const_iterator __p, _BiIter __f, _BiIter __l,
                               typename enable_if<__is_cpp17_bidirectional_iterator<_BiIter>::value>::type*)
{
    size_type __n = _VSTD::distance(__f, __l);
    size_type __pos = __p - begin();
    size_type __to_end = size() - __pos;
    allocator_type& __a = __alloc();
    if (__pos < __to_end)
    {   // insert by shifting things backward
        if (__n > __front_spare())
            __add_front_capacity(__n - __front_spare());
        // __n <= __front_spare()
        iterator __old_begin = begin();
        iterator __i = __old_begin;
        _BiIter __m = __f;
        if (__n > __pos)
        {
            __m = __pos < __n / 2 ? _VSTD::prev(__l, __pos) : _VSTD::next(__f, __n - __pos);
            for (_BiIter __j = __m; __j != __f; --__start_, ++__size())
                __alloc_traits::construct(__a, _VSTD::addressof(*--__i), *--__j);
            __n = __pos;
        }
        if (__n > 0)
        {
            iterator __obn = __old_begin + __n;
            for (iterator __j = __obn; __j != __old_begin;)
            {
                __alloc_traits::construct(__a, _VSTD::addressof(*--__i), _VSTD::move(*--__j));
                --__start_;
                ++__size();
            }
            if (__n < __pos)
                __old_begin = _VSTD::move(__obn, __old_begin + __pos, __old_begin);
            _VSTD::copy(__m, __l, __old_begin);
        }
    }
    else
    {   // insert by shifting things forward
        size_type __back_capacity = __back_spare();
        if (__n > __back_capacity)
            __add_back_capacity(__n - __back_capacity);
        // __n <= __back_capacity
        iterator __old_end = end();
        iterator __i = __old_end;
        _BiIter __m = __l;
        size_type __de = size() - __pos;
        if (__n > __de)
        {
            __m = __de < __n / 2 ? _VSTD::next(__f, __de) : _VSTD::prev(__l, __n - __de);
            for (_BiIter __j = __m; __j != __l; ++__i, (void) ++__j, ++__size())
                __alloc_traits::construct(__a, _VSTD::addressof(*__i), *__j);
            __n = __de;
        }
        if (__n > 0)
        {
            iterator __oen = __old_end - __n;
            for (iterator __j = __oen; __j != __old_end; ++__i, (void) ++__j, ++__size())
                __alloc_traits::construct(__a, _VSTD::addressof(*__i), _VSTD::move(*__j));
            if (__n < __de)
                __old_end = _VSTD::move_backward(__old_end - __de, __oen, __old_end);
            _VSTD::copy_backward(__f, __m, __old_end);
        }
    }
    return begin() + __pos;
}

template <class _Tp, class _Allocator>
template <class _InpIter>
void
deque<_Tp, _Allocator>::__append(_InpIter __f, _InpIter __l,
                                 typename enable_if<__is_exactly_cpp17_input_iterator<_InpIter>::value>::type*)
{
    for (; __f != __l; ++__f)
#ifdef _LIBCPP_CXX03_LANG
        push_back(*__f);
#else
        emplace_back(*__f);
#endif
}

template <class _Tp, class _Allocator>
template <class _ForIter>
void
deque<_Tp, _Allocator>::__append(_ForIter __f, _ForIter __l,
                                 typename enable_if<__is_cpp17_forward_iterator<_ForIter>::value>::type*)
{
    size_type __n = _VSTD::distance(__f, __l);
    allocator_type& __a = __alloc();
    size_type __back_capacity = __back_spare();
    if (__n > __back_capacity)
        __add_back_capacity(__n - __back_capacity);
    // __n <= __back_capacity
    for (__deque_block_range __br : __deque_range(end(), end() + __n)) {
      _ConstructTransaction __tx(this, __br);
      for (; __tx.__pos_ != __tx.__end_; ++__tx.__pos_, (void)++__f) {
        __alloc_traits::construct(__a, _VSTD::__to_address(__tx.__pos_), *__f);
      }
    }
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::__append(size_type __n)
{
    allocator_type& __a = __alloc();
    size_type __back_capacity = __back_spare();
    if (__n > __back_capacity)
        __add_back_capacity(__n - __back_capacity);
    // __n <= __back_capacity
    for (__deque_block_range __br : __deque_range(end(), end() + __n)) {
      _ConstructTransaction __tx(this, __br);
      for (; __tx.__pos_ != __tx.__end_; ++__tx.__pos_) {
        __alloc_traits::construct(__a, _VSTD::__to_address(__tx.__pos_));
      }
    }
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::__append(size_type __n, const value_type& __v)
{
    allocator_type& __a = __alloc();
    size_type __back_capacity = __back_spare();
    if (__n > __back_capacity)
        __add_back_capacity(__n - __back_capacity);
    // __n <= __back_capacity
    for (__deque_block_range __br : __deque_range(end(), end() + __n)) {
      _ConstructTransaction __tx(this, __br);
      for (; __tx.__pos_ != __tx.__end_; ++__tx.__pos_) {
        __alloc_traits::construct(__a, _VSTD::__to_address(__tx.__pos_), __v);
      }
    }

}

// Create front capacity for one block of elements.
// Strong guarantee.  Either do it or don't touch anything.
template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::__add_front_capacity()
{
    allocator_type& __a = __alloc();
    if (__back_spare() >= __block_size)
    {
        __start_ += __block_size;
        pointer __pt = __map_.back();
        __map_.pop_back();
        __map_.push_front(__pt);
    }
    // Else if __map_.size() < __map_.capacity() then we need to allocate 1 buffer
    else if (__map_.size() < __map_.capacity())
    {   // we can put the new buffer into the map, but don't shift things around
        // until all buffers are allocated.  If we throw, we don't need to fix
        // anything up (any added buffers are undetectible)
        if (__map_.__front_spare() > 0)
            __map_.push_front(__alloc_traits::allocate(__a, __block_size));
        else
        {
            __map_.push_back(__alloc_traits::allocate(__a, __block_size));
            // Done allocating, reorder capacity
            pointer __pt = __map_.back();
            __map_.pop_back();
            __map_.push_front(__pt);
        }
        __start_ = __map_.size() == 1 ?
                               __block_size / 2 :
                               __start_ + __block_size;
    }
    // Else need to allocate 1 buffer, *and* we need to reallocate __map_.
    else
    {
        __split_buffer<pointer, __pointer_allocator&>
            __buf(max<size_type>(2 * __map_.capacity(), 1),
                  0, __map_.__alloc());

        typedef __allocator_destructor<_Allocator> _Dp;
        unique_ptr<pointer, _Dp> __hold(
            __alloc_traits::allocate(__a, __block_size),
                _Dp(__a, __block_size));
        __buf.push_back(__hold.get());
        __hold.release();

        for (__map_pointer __i = __map_.begin();
                __i != __map_.end(); ++__i)
            __buf.push_back(*__i);
        _VSTD::swap(__map_.__first_, __buf.__first_);
        _VSTD::swap(__map_.__begin_, __buf.__begin_);
        _VSTD::swap(__map_.__end_, __buf.__end_);
        _VSTD::swap(__map_.__end_cap(), __buf.__end_cap());
        __start_ = __map_.size() == 1 ?
                               __block_size / 2 :
                               __start_ + __block_size;
    }
}

// Create front capacity for __n elements.
// Strong guarantee.  Either do it or don't touch anything.
template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::__add_front_capacity(size_type __n)
{
    allocator_type& __a = __alloc();
    size_type __nb = __recommend_blocks(__n + __map_.empty());
    // Number of unused blocks at back:
    size_type __back_capacity = __back_spare() / __block_size;
    __back_capacity = _VSTD::min(__back_capacity, __nb);  // don't take more than you need
    __nb -= __back_capacity;  // number of blocks need to allocate
    // If __nb == 0, then we have sufficient capacity.
    if (__nb == 0)
    {
        __start_ += __block_size * __back_capacity;
        for (; __back_capacity > 0; --__back_capacity)
        {
            pointer __pt = __map_.back();
            __map_.pop_back();
            __map_.push_front(__pt);
        }
    }
    // Else if __nb <= __map_.capacity() - __map_.size() then we need to allocate __nb buffers
    else if (__nb <= __map_.capacity() - __map_.size())
    {   // we can put the new buffers into the map, but don't shift things around
        // until all buffers are allocated.  If we throw, we don't need to fix
        // anything up (any added buffers are undetectible)
        for (; __nb > 0; --__nb, __start_ += __block_size - (__map_.size() == 1))
        {
            if (__map_.__front_spare() == 0)
                break;
            __map_.push_front(__alloc_traits::allocate(__a, __block_size));
        }
        for (; __nb > 0; --__nb, ++__back_capacity)
            __map_.push_back(__alloc_traits::allocate(__a, __block_size));
        // Done allocating, reorder capacity
        __start_ += __back_capacity * __block_size;
        for (; __back_capacity > 0; --__back_capacity)
        {
            pointer __pt = __map_.back();
            __map_.pop_back();
            __map_.push_front(__pt);
        }
    }
    // Else need to allocate __nb buffers, *and* we need to reallocate __map_.
    else
    {
        size_type __ds = (__nb + __back_capacity) * __block_size - __map_.empty();
        __split_buffer<pointer, __pointer_allocator&>
            __buf(max<size_type>(2* __map_.capacity(),
                                 __nb + __map_.size()),
                  0, __map_.__alloc());
#ifndef _LIBCPP_NO_EXCEPTIONS
        try
        {
#endif // _LIBCPP_NO_EXCEPTIONS
            for (; __nb > 0; --__nb)
                __buf.push_back(__alloc_traits::allocate(__a, __block_size));
#ifndef _LIBCPP_NO_EXCEPTIONS
        }
        catch (...)
        {
            for (__map_pointer __i = __buf.begin();
                    __i != __buf.end(); ++__i)
                __alloc_traits::deallocate(__a, *__i, __block_size);
            throw;
        }
#endif // _LIBCPP_NO_EXCEPTIONS
        for (; __back_capacity > 0; --__back_capacity)
        {
            __buf.push_back(__map_.back());
            __map_.pop_back();
        }
        for (__map_pointer __i = __map_.begin();
                __i != __map_.end(); ++__i)
            __buf.push_back(*__i);
        _VSTD::swap(__map_.__first_, __buf.__first_);
        _VSTD::swap(__map_.__begin_, __buf.__begin_);
        _VSTD::swap(__map_.__end_, __buf.__end_);
        _VSTD::swap(__map_.__end_cap(), __buf.__end_cap());
        __start_ += __ds;
    }
}

// Create back capacity for one block of elements.
// Strong guarantee.  Either do it or don't touch anything.
template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::__add_back_capacity()
{
    allocator_type& __a = __alloc();
    if (__front_spare() >= __block_size)
    {
        __start_ -= __block_size;
        pointer __pt = __map_.front();
        __map_.pop_front();
        __map_.push_back(__pt);
    }
    // Else if __nb <= __map_.capacity() - __map_.size() then we need to allocate __nb buffers
    else if (__map_.size() < __map_.capacity())
    {   // we can put the new buffer into the map, but don't shift things around
        // until it is allocated.  If we throw, we don't need to fix
        // anything up (any added buffers are undetectible)
        if (__map_.__back_spare() != 0)
            __map_.push_back(__alloc_traits::allocate(__a, __block_size));
        else
        {
            __map_.push_front(__alloc_traits::allocate(__a, __block_size));
            // Done allocating, reorder capacity
            pointer __pt = __map_.front();
            __map_.pop_front();
            __map_.push_back(__pt);
        }
    }
    // Else need to allocate 1 buffer, *and* we need to reallocate __map_.
    else
    {
        __split_buffer<pointer, __pointer_allocator&>
            __buf(max<size_type>(2* __map_.capacity(), 1),
                  __map_.size(),
                  __map_.__alloc());

        typedef __allocator_destructor<_Allocator> _Dp;
        unique_ptr<pointer, _Dp> __hold(
            __alloc_traits::allocate(__a, __block_size),
                _Dp(__a, __block_size));
        __buf.push_back(__hold.get());
        __hold.release();

        for (__map_pointer __i = __map_.end();
                __i != __map_.begin();)
            __buf.push_front(*--__i);
        _VSTD::swap(__map_.__first_, __buf.__first_);
        _VSTD::swap(__map_.__begin_, __buf.__begin_);
        _VSTD::swap(__map_.__end_, __buf.__end_);
        _VSTD::swap(__map_.__end_cap(), __buf.__end_cap());
    }
}

// Create back capacity for __n elements.
// Strong guarantee.  Either do it or don't touch anything.
template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::__add_back_capacity(size_type __n)
{
    allocator_type& __a = __alloc();
    size_type __nb = __recommend_blocks(__n + __map_.empty());
    // Number of unused blocks at front:
    size_type __front_capacity = __front_spare() / __block_size;
    __front_capacity = _VSTD::min(__front_capacity, __nb);  // don't take more than you need
    __nb -= __front_capacity;  // number of blocks need to allocate
    // If __nb == 0, then we have sufficient capacity.
    if (__nb == 0)
    {
        __start_ -= __block_size * __front_capacity;
        for (; __front_capacity > 0; --__front_capacity)
        {
            pointer __pt = __map_.front();
            __map_.pop_front();
            __map_.push_back(__pt);
        }
    }
    // Else if __nb <= __map_.capacity() - __map_.size() then we need to allocate __nb buffers
    else if (__nb <= __map_.capacity() - __map_.size())
    {   // we can put the new buffers into the map, but don't shift things around
        // until all buffers are allocated.  If we throw, we don't need to fix
        // anything up (any added buffers are undetectible)
        for (; __nb > 0; --__nb)
        {
            if (__map_.__back_spare() == 0)
                break;
            __map_.push_back(__alloc_traits::allocate(__a, __block_size));
        }
        for (; __nb > 0; --__nb, ++__front_capacity, __start_ +=
                                 __block_size - (__map_.size() == 1))
            __map_.push_front(__alloc_traits::allocate(__a, __block_size));
        // Done allocating, reorder capacity
        __start_ -= __block_size * __front_capacity;
        for (; __front_capacity > 0; --__front_capacity)
        {
            pointer __pt = __map_.front();
            __map_.pop_front();
            __map_.push_back(__pt);
        }
    }
    // Else need to allocate __nb buffers, *and* we need to reallocate __map_.
    else
    {
        size_type __ds = __front_capacity * __block_size;
        __split_buffer<pointer, __pointer_allocator&>
            __buf(max<size_type>(2* __map_.capacity(),
                                 __nb + __map_.size()),
                  __map_.size() - __front_capacity,
                  __map_.__alloc());
#ifndef _LIBCPP_NO_EXCEPTIONS
        try
        {
#endif // _LIBCPP_NO_EXCEPTIONS
            for (; __nb > 0; --__nb)
                __buf.push_back(__alloc_traits::allocate(__a, __block_size));
#ifndef _LIBCPP_NO_EXCEPTIONS
        }
        catch (...)
        {
            for (__map_pointer __i = __buf.begin();
                    __i != __buf.end(); ++__i)
                __alloc_traits::deallocate(__a, *__i, __block_size);
            throw;
        }
#endif // _LIBCPP_NO_EXCEPTIONS
        for (; __front_capacity > 0; --__front_capacity)
        {
            __buf.push_back(__map_.front());
            __map_.pop_front();
        }
        for (__map_pointer __i = __map_.end();
                __i != __map_.begin();)
            __buf.push_front(*--__i);
        _VSTD::swap(__map_.__first_, __buf.__first_);
        _VSTD::swap(__map_.__begin_, __buf.__begin_);
        _VSTD::swap(__map_.__end_, __buf.__end_);
        _VSTD::swap(__map_.__end_cap(), __buf.__end_cap());
        __start_ -= __ds;
    }
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::pop_front()
{
    allocator_type& __a = __alloc();
    __alloc_traits::destroy(__a, _VSTD::__to_address(*(__map_.begin() +
                                                    __start_ / __block_size) +
                                                    __start_ % __block_size));
    --__size();
    ++__start_;
    __maybe_remove_front_spare();
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::pop_back()
{
    _LIBCPP_ASSERT(!empty(), "deque::pop_back called on an empty deque");
    allocator_type& __a = __alloc();
    size_type __p = size() + __start_ - 1;
    __alloc_traits::destroy(__a, _VSTD::__to_address(*(__map_.begin() +
                                                    __p / __block_size) +
                                                    __p % __block_size));
    --__size();
    __maybe_remove_back_spare();
}

// move assign [__f, __l) to [__r, __r + (__l-__f)).
// If __vt points into [__f, __l), then subtract (__f - __r) from __vt.
template <class _Tp, class _Allocator>
typename deque<_Tp, _Allocator>::iterator
deque<_Tp, _Allocator>::__move_and_check(iterator __f, iterator __l, iterator __r,
                                         const_pointer& __vt)
{
    // as if
    //   for (; __f != __l; ++__f, ++__r)
    //       *__r = _VSTD::move(*__f);
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        pointer __fb = __f.__ptr_;
        pointer __fe = *__f.__m_iter_ + __block_size;
        difference_type __bs = __fe - __fb;
        if (__bs > __n)
        {
            __bs = __n;
            __fe = __fb + __bs;
        }
        if (__fb <= __vt && __vt < __fe)
            __vt = (const_iterator(static_cast<__map_const_pointer>(__f.__m_iter_), __vt) -= __f - __r).__ptr_;
        __r = _VSTD::move(__fb, __fe, __r);
        __n -= __bs;
        __f += __bs;
    }
    return __r;
}

// move assign [__f, __l) to [__r - (__l-__f), __r) backwards.
// If __vt points into [__f, __l), then add (__r - __l) to __vt.
template <class _Tp, class _Allocator>
typename deque<_Tp, _Allocator>::iterator
deque<_Tp, _Allocator>::__move_backward_and_check(iterator __f, iterator __l, iterator __r,
                                                  const_pointer& __vt)
{
    // as if
    //   while (__f != __l)
    //       *--__r = _VSTD::move(*--__l);
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        --__l;
        pointer __lb = *__l.__m_iter_;
        pointer __le = __l.__ptr_ + 1;
        difference_type __bs = __le - __lb;
        if (__bs > __n)
        {
            __bs = __n;
            __lb = __le - __bs;
        }
        if (__lb <= __vt && __vt < __le)
            __vt = (const_iterator(static_cast<__map_const_pointer>(__l.__m_iter_), __vt) += __r - __l - 1).__ptr_;
        __r = _VSTD::move_backward(__lb, __le, __r);
        __n -= __bs;
        __l -= __bs - 1;
    }
    return __r;
}

// move construct [__f, __l) to [__r, __r + (__l-__f)).
// If __vt points into [__f, __l), then add (__r - __f) to __vt.
template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::__move_construct_and_check(iterator __f, iterator __l,
                                                   iterator __r, const_pointer& __vt)
{
    allocator_type& __a = __alloc();
    // as if
    //   for (; __f != __l; ++__r, ++__f, ++__size())
    //       __alloc_traits::construct(__a, _VSTD::addressof(*__r), _VSTD::move(*__f));
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        pointer __fb = __f.__ptr_;
        pointer __fe = *__f.__m_iter_ + __block_size;
        difference_type __bs = __fe - __fb;
        if (__bs > __n)
        {
            __bs = __n;
            __fe = __fb + __bs;
        }
        if (__fb <= __vt && __vt < __fe)
            __vt = (const_iterator(static_cast<__map_const_pointer>(__f.__m_iter_), __vt) += __r - __f).__ptr_;
        for (; __fb != __fe; ++__fb, ++__r, ++__size())
            __alloc_traits::construct(__a, _VSTD::addressof(*__r), _VSTD::move(*__fb));
        __n -= __bs;
        __f += __bs;
    }
}

// move construct [__f, __l) to [__r - (__l-__f), __r) backwards.
// If __vt points into [__f, __l), then subtract (__l - __r) from __vt.
template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::__move_construct_backward_and_check(iterator __f, iterator __l,
                                                            iterator __r, const_pointer& __vt)
{
    allocator_type& __a = __alloc();
    // as if
    //   for (iterator __j = __l; __j != __f;)
    //   {
    //       __alloc_traitsconstruct(__a, _VSTD::addressof(*--__r), _VSTD::move(*--__j));
    //       --__start_;
    //       ++__size();
    //   }
    difference_type __n = __l - __f;
    while (__n > 0)
    {
        --__l;
        pointer __lb = *__l.__m_iter_;
        pointer __le = __l.__ptr_ + 1;
        difference_type __bs = __le - __lb;
        if (__bs > __n)
        {
            __bs = __n;
            __lb = __le - __bs;
        }
        if (__lb <= __vt && __vt < __le)
            __vt = (const_iterator(static_cast<__map_const_pointer>(__l.__m_iter_), __vt) -= __l - __r + 1).__ptr_;
        while (__le != __lb)
        {
            __alloc_traits::construct(__a, _VSTD::addressof(*--__r), _VSTD::move(*--__le));
            --__start_;
            ++__size();
        }
        __n -= __bs;
        __l -= __bs - 1;
    }
}

template <class _Tp, class _Allocator>
typename deque<_Tp, _Allocator>::iterator
deque<_Tp, _Allocator>::erase(const_iterator __f)
{
    iterator __b = begin();
    difference_type __pos = __f - __b;
    iterator __p = __b + __pos;
    allocator_type& __a = __alloc();
    if (static_cast<size_t>(__pos) <= (size() - 1) / 2)
    {   // erase from front
        _VSTD::move_backward(__b, __p, _VSTD::next(__p));
        __alloc_traits::destroy(__a, _VSTD::addressof(*__b));
        --__size();
        ++__start_;
        __maybe_remove_front_spare();
    }
    else
    {   // erase from back
        iterator __i = _VSTD::move(_VSTD::next(__p), end(), __p);
        __alloc_traits::destroy(__a, _VSTD::addressof(*__i));
        --__size();
        __maybe_remove_back_spare();
    }
    return begin() + __pos;
}

template <class _Tp, class _Allocator>
typename deque<_Tp, _Allocator>::iterator
deque<_Tp, _Allocator>::erase(const_iterator __f, const_iterator __l)
{
    difference_type __n = __l - __f;
    iterator __b = begin();
    difference_type __pos = __f - __b;
    iterator __p = __b + __pos;
    if (__n > 0)
    {
        allocator_type& __a = __alloc();
        if (static_cast<size_t>(__pos) <= (size() - __n) / 2)
        {   // erase from front
            iterator __i = _VSTD::move_backward(__b, __p, __p + __n);
            for (; __b != __i; ++__b)
                __alloc_traits::destroy(__a, _VSTD::addressof(*__b));
            __size() -= __n;
            __start_ += __n;
            while (__maybe_remove_front_spare()) {
            }
        }
        else
        {   // erase from back
            iterator __i = _VSTD::move(__p + __n, end(), __p);
            for (iterator __e = end(); __i != __e; ++__i)
                __alloc_traits::destroy(__a, _VSTD::addressof(*__i));
            __size() -= __n;
            while (__maybe_remove_back_spare()) {
            }
        }
    }
    return begin() + __pos;
}

template <class _Tp, class _Allocator>
void
deque<_Tp, _Allocator>::__erase_to_end(const_iterator __f)
{
    iterator __e = end();
    difference_type __n = __e - __f;
    if (__n > 0)
    {
        allocator_type& __a = __alloc();
        iterator __b = begin();
        difference_type __pos = __f - __b;
        for (iterator __p = __b + __pos; __p != __e; ++__p)
            __alloc_traits::destroy(__a, _VSTD::addressof(*__p));
        __size() -= __n;
        while (__maybe_remove_back_spare()) {
        }
    }
}

template <class _Tp, class _Allocator>
inline
void
deque<_Tp, _Allocator>::swap(deque& __c)
#if _LIBCPP_STD_VER >= 14
        _NOEXCEPT
#else
        _NOEXCEPT_(!__alloc_traits::propagate_on_container_swap::value ||
                    __is_nothrow_swappable<allocator_type>::value)
#endif
{
    __map_.swap(__c.__map_);
    _VSTD::swap(__start_, __c.__start_);
    _VSTD::swap(__size(), __c.__size());
    _VSTD::__swap_allocator(__alloc(), __c.__alloc());
}

template <class _Tp, class _Allocator>
inline
void
deque<_Tp, _Allocator>::clear() _NOEXCEPT
{
    allocator_type& __a = __alloc();
    for (iterator __i = begin(), __e = end(); __i != __e; ++__i)
        __alloc_traits::destroy(__a, _VSTD::addressof(*__i));
    __size() = 0;
    while (__map_.size() > 2)
    {
        __alloc_traits::deallocate(__a, __map_.front(), __block_size);
        __map_.pop_front();
    }
    switch (__map_.size())
    {
    case 1:
        __start_ = __block_size / 2;
        break;
    case 2:
        __start_ = __block_size;
        break;
    }
}

template <class _Tp, class _Allocator>
inline _LIBCPP_HIDE_FROM_ABI
bool
operator==(const deque<_Tp, _Allocator>& __x, const deque<_Tp, _Allocator>& __y)
{
    const typename deque<_Tp, _Allocator>::size_type __sz = __x.size();
    return __sz == __y.size() && _VSTD::equal(__x.begin(), __x.end(), __y.begin());
}

template <class _Tp, class _Allocator>
inline _LIBCPP_HIDE_FROM_ABI
bool
operator!=(const deque<_Tp, _Allocator>& __x, const deque<_Tp, _Allocator>& __y)
{
    return !(__x == __y);
}

template <class _Tp, class _Allocator>
inline _LIBCPP_HIDE_FROM_ABI
bool
operator< (const deque<_Tp, _Allocator>& __x, const deque<_Tp, _Allocator>& __y)
{
    return _VSTD::lexicographical_compare(__x.begin(), __x.end(), __y.begin(), __y.end());
}

template <class _Tp, class _Allocator>
inline _LIBCPP_HIDE_FROM_ABI
bool
operator> (const deque<_Tp, _Allocator>& __x, const deque<_Tp, _Allocator>& __y)
{
    return __y < __x;
}

template <class _Tp, class _Allocator>
inline _LIBCPP_HIDE_FROM_ABI
bool
operator>=(const deque<_Tp, _Allocator>& __x, const deque<_Tp, _Allocator>& __y)
{
    return !(__x < __y);
}

template <class _Tp, class _Allocator>
inline _LIBCPP_HIDE_FROM_ABI
bool
operator<=(const deque<_Tp, _Allocator>& __x, const deque<_Tp, _Allocator>& __y)
{
    return !(__y < __x);
}

template <class _Tp, class _Allocator>
inline _LIBCPP_HIDE_FROM_ABI
void
swap(deque<_Tp, _Allocator>& __x, deque<_Tp, _Allocator>& __y)
    _NOEXCEPT_(_NOEXCEPT_(__x.swap(__y)))
{
    __x.swap(__y);
}

#if _LIBCPP_STD_VER > 17
template <class _Tp, class _Allocator, class _Up>
inline _LIBCPP_HIDE_FROM_ABI typename deque<_Tp, _Allocator>::size_type
erase(deque<_Tp, _Allocator>& __c, const _Up& __v) {
  auto __old_size = __c.size();
  __c.erase(_VSTD::remove(__c.begin(), __c.end(), __v), __c.end());
  return __old_size - __c.size();
}

template <class _Tp, class _Allocator, class _Predicate>
inline _LIBCPP_HIDE_FROM_ABI typename deque<_Tp, _Allocator>::size_type
erase_if(deque<_Tp, _Allocator>& __c, _Predicate __pred) {
  auto __old_size = __c.size();
  __c.erase(_VSTD::remove_if(__c.begin(), __c.end(), __pred), __c.end());
  return __old_size - __c.size();
}

template <>
inline constexpr bool __format::__enable_insertable<std::deque<char>> = true;
#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
template <>
inline constexpr bool __format::__enable_insertable<std::deque<wchar_t>> = true;
#endif

#endif // _LIBCPP_STD_VER > 17

_LIBCPP_END_NAMESPACE_STD

#if _LIBCPP_STD_VER > 14
_LIBCPP_BEGIN_NAMESPACE_STD
namespace pmr {
template <class _ValueT>
using deque = std::deque<_ValueT, polymorphic_allocator<_ValueT>>;
} // namespace pmr
_LIBCPP_END_NAMESPACE_STD
#endif

_LIBCPP_POP_MACROS

#if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
#  include <algorithm>
#  include <atomic>
#  include <concepts>
#  include <functional>
#  include <iosfwd>
#  include <iterator>
#  include <typeinfo>
#endif

#endif // _LIBCPP_DEQUE
