// -*- 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___HASH_TABLE
#define _LIBCPP___HASH_TABLE

#include <__algorithm/max.h>
#include <__algorithm/min.h>
#include <__assert>
#include <__bit/countl.h>
#include <__config>
#include <__debug>
#include <__functional/hash.h>
#include <__iterator/iterator_traits.h>
#include <__memory/addressof.h>
#include <__memory/allocator_traits.h>
#include <__memory/compressed_pair.h>
#include <__memory/pointer_traits.h>
#include <__memory/swap_allocator.h>
#include <__memory/unique_ptr.h>
#include <__type_traits/can_extract_key.h>
#include <__utility/forward.h>
#include <__utility/move.h>
#include <__utility/pair.h>
#include <__utility/swap.h>
#include <cmath>
#include <cstring>
#include <initializer_list>
#include <type_traits>

#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 _Key, class _Tp>
struct __hash_value_type;

template <class _Tp>
struct __is_hash_value_type_imp : false_type {};

template <class _Key, class _Value>
struct __is_hash_value_type_imp<__hash_value_type<_Key, _Value> > : true_type {};

template <class ..._Args>
struct __is_hash_value_type : false_type {};

template <class _One>
struct __is_hash_value_type<_One> : __is_hash_value_type_imp<__remove_cvref_t<_One> > {};

_LIBCPP_FUNC_VIS
size_t __next_prime(size_t __n);

template <class _NodePtr>
struct __hash_node_base
{
    typedef typename pointer_traits<_NodePtr>::element_type __node_type;
    typedef __hash_node_base __first_node;
    typedef __rebind_pointer_t<_NodePtr, __first_node> __node_base_pointer;
    typedef _NodePtr __node_pointer;

#if defined(_LIBCPP_ABI_FIX_UNORDERED_NODE_POINTER_UB)
  typedef __node_base_pointer __next_pointer;
#else
    typedef __conditional_t<is_pointer<__node_pointer>::value, __node_base_pointer, __node_pointer> __next_pointer;
#endif

    __next_pointer    __next_;

    _LIBCPP_INLINE_VISIBILITY
    __next_pointer __ptr() _NOEXCEPT {
        return static_cast<__next_pointer>(
            pointer_traits<__node_base_pointer>::pointer_to(*this));
    }

    _LIBCPP_INLINE_VISIBILITY
    __node_pointer __upcast() _NOEXCEPT {
        return static_cast<__node_pointer>(
            pointer_traits<__node_base_pointer>::pointer_to(*this));
    }

    _LIBCPP_INLINE_VISIBILITY
    size_t __hash() const _NOEXCEPT {
        return static_cast<__node_type const&>(*this).__hash_;
    }

    _LIBCPP_INLINE_VISIBILITY __hash_node_base() _NOEXCEPT : __next_(nullptr) {}
};

template <class _Tp, class _VoidPtr>
struct _LIBCPP_STANDALONE_DEBUG __hash_node
    : public __hash_node_base
             <
                 __rebind_pointer_t<_VoidPtr, __hash_node<_Tp, _VoidPtr> >
             >
{
    typedef _Tp __node_value_type;

    size_t            __hash_;
    __node_value_type __value_;
};

inline _LIBCPP_INLINE_VISIBILITY
bool
__is_hash_power2(size_t __bc)
{
    return __bc > 2 && !(__bc & (__bc - 1));
}

inline _LIBCPP_INLINE_VISIBILITY
size_t
__constrain_hash(size_t __h, size_t __bc)
{
    return !(__bc & (__bc - 1)) ? __h & (__bc - 1) :
        (__h < __bc ? __h : __h % __bc);
}

inline _LIBCPP_INLINE_VISIBILITY
size_t
__next_hash_pow2(size_t __n)
{
    return __n < 2 ? __n : (size_t(1) << (numeric_limits<size_t>::digits - __libcpp_clz(__n-1)));
}


template <class _Tp, class _Hash, class _Equal, class _Alloc> class __hash_table;

template <class _NodePtr>      class _LIBCPP_TEMPLATE_VIS __hash_iterator;
template <class _ConstNodePtr> class _LIBCPP_TEMPLATE_VIS __hash_const_iterator;
template <class _NodePtr>      class _LIBCPP_TEMPLATE_VIS __hash_local_iterator;
template <class _ConstNodePtr> class _LIBCPP_TEMPLATE_VIS __hash_const_local_iterator;
template <class _HashIterator> class _LIBCPP_TEMPLATE_VIS __hash_map_iterator;
template <class _HashIterator> class _LIBCPP_TEMPLATE_VIS __hash_map_const_iterator;

template <class _Tp>
struct __hash_key_value_types {
  static_assert(!is_reference<_Tp>::value && !is_const<_Tp>::value, "");
  typedef _Tp key_type;
  typedef _Tp __node_value_type;
  typedef _Tp __container_value_type;
  static const bool __is_map = false;

  _LIBCPP_INLINE_VISIBILITY
  static key_type const& __get_key(_Tp const& __v) {
    return __v;
  }
  _LIBCPP_INLINE_VISIBILITY
  static __container_value_type const& __get_value(__node_value_type const& __v) {
    return __v;
  }
  _LIBCPP_INLINE_VISIBILITY
  static __container_value_type* __get_ptr(__node_value_type& __n) {
    return _VSTD::addressof(__n);
  }
  _LIBCPP_INLINE_VISIBILITY
  static __container_value_type&& __move(__node_value_type& __v) {
    return _VSTD::move(__v);
  }
};

template <class _Key, class _Tp>
struct __hash_key_value_types<__hash_value_type<_Key, _Tp> > {
  typedef _Key                                         key_type;
  typedef _Tp                                          mapped_type;
  typedef __hash_value_type<_Key, _Tp>                 __node_value_type;
  typedef pair<const _Key, _Tp>                        __container_value_type;
  typedef __container_value_type                       __map_value_type;
  static const bool __is_map = true;

  _LIBCPP_INLINE_VISIBILITY
  static key_type const& __get_key(__container_value_type const& __v) {
    return __v.first;
  }

  template <class _Up>
  _LIBCPP_INLINE_VISIBILITY
  static __enable_if_t<__is_same_uncvref<_Up, __node_value_type>::value, __container_value_type const&>
  __get_value(_Up& __t) {
    return __t.__get_value();
  }

  template <class _Up>
  _LIBCPP_INLINE_VISIBILITY
  static __enable_if_t<__is_same_uncvref<_Up, __container_value_type>::value, __container_value_type const&>
  __get_value(_Up& __t) {
    return __t;
  }

  _LIBCPP_INLINE_VISIBILITY
  static __container_value_type* __get_ptr(__node_value_type& __n) {
    return _VSTD::addressof(__n.__get_value());
  }
  _LIBCPP_INLINE_VISIBILITY
  static pair<key_type&&, mapped_type&&> __move(__node_value_type& __v) {
    return __v.__move();
  }
};

template <class _Tp, class _AllocPtr, class _KVTypes = __hash_key_value_types<_Tp>,
          bool = _KVTypes::__is_map>
struct __hash_map_pointer_types {};

template <class _Tp, class _AllocPtr, class _KVTypes>
struct __hash_map_pointer_types<_Tp, _AllocPtr, _KVTypes, true> {
  typedef typename _KVTypes::__map_value_type   _Mv;
  typedef __rebind_pointer_t<_AllocPtr, _Mv>
                                                       __map_value_type_pointer;
  typedef __rebind_pointer_t<_AllocPtr, const _Mv>
                                                 __const_map_value_type_pointer;
};

template <class _NodePtr, class _NodeT = typename pointer_traits<_NodePtr>::element_type>
struct __hash_node_types;

template <class _NodePtr, class _Tp, class _VoidPtr>
struct __hash_node_types<_NodePtr, __hash_node<_Tp, _VoidPtr> >
    : public __hash_key_value_types<_Tp>, __hash_map_pointer_types<_Tp, _VoidPtr>

{
  typedef __hash_key_value_types<_Tp>           __base;

public:
  typedef ptrdiff_t difference_type;
  typedef size_t size_type;

  typedef __rebind_pointer_t<_NodePtr, void>       __void_pointer;

  typedef typename pointer_traits<_NodePtr>::element_type       __node_type;
  typedef _NodePtr                                              __node_pointer;

  typedef __hash_node_base<__node_pointer>                      __node_base_type;
  typedef __rebind_pointer_t<_NodePtr, __node_base_type>
                                                             __node_base_pointer;

  typedef typename __node_base_type::__next_pointer          __next_pointer;

  typedef _Tp                                                 __node_value_type;
  typedef __rebind_pointer_t<_VoidPtr, __node_value_type>
                                                      __node_value_type_pointer;
  typedef __rebind_pointer_t<_VoidPtr, const __node_value_type>
                                                __const_node_value_type_pointer;

private:
    static_assert(!is_const<__node_type>::value,
                "_NodePtr should never be a pointer to const");
    static_assert((is_same<typename pointer_traits<_VoidPtr>::element_type, void>::value),
                  "_VoidPtr does not point to unqualified void type");
    static_assert((is_same<__rebind_pointer_t<_VoidPtr, __node_type>,
                          _NodePtr>::value), "_VoidPtr does not rebind to _NodePtr.");
};

template <class _HashIterator>
struct __hash_node_types_from_iterator;
template <class _NodePtr>
struct __hash_node_types_from_iterator<__hash_iterator<_NodePtr> > : __hash_node_types<_NodePtr> {};
template <class _NodePtr>
struct __hash_node_types_from_iterator<__hash_const_iterator<_NodePtr> > : __hash_node_types<_NodePtr> {};
template <class _NodePtr>
struct __hash_node_types_from_iterator<__hash_local_iterator<_NodePtr> > : __hash_node_types<_NodePtr> {};
template <class _NodePtr>
struct __hash_node_types_from_iterator<__hash_const_local_iterator<_NodePtr> > : __hash_node_types<_NodePtr> {};


template <class _NodeValueTp, class _VoidPtr>
struct __make_hash_node_types {
  typedef __hash_node<_NodeValueTp, _VoidPtr> _NodeTp;
  typedef __rebind_pointer_t<_VoidPtr, _NodeTp> _NodePtr;
  typedef __hash_node_types<_NodePtr> type;
};

template <class _NodePtr>
class _LIBCPP_TEMPLATE_VIS __hash_iterator
{
    typedef __hash_node_types<_NodePtr> _NodeTypes;
    typedef _NodePtr                            __node_pointer;
    typedef typename _NodeTypes::__next_pointer __next_pointer;

    __next_pointer            __node_;

public:
    typedef forward_iterator_tag                           iterator_category;
    typedef typename _NodeTypes::__node_value_type         value_type;
    typedef typename _NodeTypes::difference_type           difference_type;
    typedef value_type&                                    reference;
    typedef typename _NodeTypes::__node_value_type_pointer pointer;

    _LIBCPP_INLINE_VISIBILITY __hash_iterator() _NOEXCEPT : __node_(nullptr) {
        _VSTD::__debug_db_insert_i(this);
    }

#ifdef _LIBCPP_ENABLE_DEBUG_MODE
    _LIBCPP_INLINE_VISIBILITY
    __hash_iterator(const __hash_iterator& __i)
        : __node_(__i.__node_)
    {
        __get_db()->__iterator_copy(this, _VSTD::addressof(__i));
    }

    _LIBCPP_INLINE_VISIBILITY
    ~__hash_iterator()
    {
        __get_db()->__erase_i(this);
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_iterator& operator=(const __hash_iterator& __i)
    {
        if (this != _VSTD::addressof(__i))
        {
            __get_db()->__iterator_copy(this, _VSTD::addressof(__i));
            __node_ = __i.__node_;
        }
        return *this;
    }
#endif // _LIBCPP_ENABLE_DEBUG_MODE

    _LIBCPP_INLINE_VISIBILITY
    reference operator*() const {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                             "Attempted to dereference a non-dereferenceable unordered container iterator");
        return __node_->__upcast()->__value_;
    }

    _LIBCPP_INLINE_VISIBILITY
    pointer operator->() const {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                           "Attempted to dereference a non-dereferenceable unordered container iterator");
        return pointer_traits<pointer>::pointer_to(__node_->__upcast()->__value_);
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_iterator& operator++() {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                       "Attempted to increment a non-incrementable unordered container iterator");
        __node_ = __node_->__next_;
        return *this;
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_iterator operator++(int)
    {
        __hash_iterator __t(*this);
        ++(*this);
        return __t;
    }

    friend _LIBCPP_INLINE_VISIBILITY
    bool operator==(const __hash_iterator& __x, const __hash_iterator& __y)
    {
        return __x.__node_ == __y.__node_;
    }
    friend _LIBCPP_INLINE_VISIBILITY
    bool operator!=(const __hash_iterator& __x, const __hash_iterator& __y)
        {return !(__x == __y);}

private:
    _LIBCPP_INLINE_VISIBILITY
    explicit __hash_iterator(__next_pointer __node, const void* __c) _NOEXCEPT
        : __node_(__node)
        {
            (void)__c;
#ifdef _LIBCPP_ENABLE_DEBUG_MODE
            __get_db()->__insert_ic(this, __c);
#endif
        }
    template <class, class, class, class> friend class __hash_table;
    template <class> friend class _LIBCPP_TEMPLATE_VIS __hash_const_iterator;
    template <class> friend class _LIBCPP_TEMPLATE_VIS __hash_map_iterator;
    template <class, class, class, class, class> friend class _LIBCPP_TEMPLATE_VIS unordered_map;
    template <class, class, class, class, class> friend class _LIBCPP_TEMPLATE_VIS unordered_multimap;
};

template <class _NodePtr>
class _LIBCPP_TEMPLATE_VIS __hash_const_iterator
{
    static_assert(!is_const<typename pointer_traits<_NodePtr>::element_type>::value, "");
    typedef __hash_node_types<_NodePtr> _NodeTypes;
    typedef _NodePtr                            __node_pointer;
    typedef typename _NodeTypes::__next_pointer __next_pointer;

    __next_pointer __node_;

public:
    typedef __hash_iterator<_NodePtr> __non_const_iterator;

    typedef forward_iterator_tag                                 iterator_category;
    typedef typename _NodeTypes::__node_value_type               value_type;
    typedef typename _NodeTypes::difference_type                 difference_type;
    typedef const value_type&                                    reference;
    typedef typename _NodeTypes::__const_node_value_type_pointer pointer;


    _LIBCPP_INLINE_VISIBILITY __hash_const_iterator() _NOEXCEPT : __node_(nullptr) {
        _VSTD::__debug_db_insert_i(this);
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_const_iterator(const __non_const_iterator& __x) _NOEXCEPT
        : __node_(__x.__node_)
    {
#ifdef _LIBCPP_ENABLE_DEBUG_MODE
        __get_db()->__iterator_copy(this, _VSTD::addressof(__x));
#endif
    }

#ifdef _LIBCPP_ENABLE_DEBUG_MODE
    _LIBCPP_INLINE_VISIBILITY
    __hash_const_iterator(const __hash_const_iterator& __i)
        : __node_(__i.__node_)
    {
        __get_db()->__iterator_copy(this, _VSTD::addressof(__i));
    }

    _LIBCPP_INLINE_VISIBILITY
    ~__hash_const_iterator()
    {
        __get_db()->__erase_i(this);
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_const_iterator& operator=(const __hash_const_iterator& __i)
    {
        if (this != _VSTD::addressof(__i))
        {
            __get_db()->__iterator_copy(this, _VSTD::addressof(__i));
            __node_ = __i.__node_;
        }
        return *this;
    }
#endif // _LIBCPP_ENABLE_DEBUG_MODE

    _LIBCPP_INLINE_VISIBILITY
    reference operator*() const {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                           "Attempted to dereference a non-dereferenceable unordered container const_iterator");
        return __node_->__upcast()->__value_;
    }
    _LIBCPP_INLINE_VISIBILITY
    pointer operator->() const {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                           "Attempted to dereference a non-dereferenceable unordered container const_iterator");
        return pointer_traits<pointer>::pointer_to(__node_->__upcast()->__value_);
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_const_iterator& operator++() {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                             "Attempted to increment a non-incrementable unordered container const_iterator");
        __node_ = __node_->__next_;
        return *this;
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_const_iterator operator++(int)
    {
        __hash_const_iterator __t(*this);
        ++(*this);
        return __t;
    }

    friend _LIBCPP_INLINE_VISIBILITY
    bool operator==(const __hash_const_iterator& __x, const __hash_const_iterator& __y)
    {
        return __x.__node_ == __y.__node_;
    }
    friend _LIBCPP_INLINE_VISIBILITY
    bool operator!=(const __hash_const_iterator& __x, const __hash_const_iterator& __y)
        {return !(__x == __y);}

private:
    _LIBCPP_INLINE_VISIBILITY
    explicit __hash_const_iterator(__next_pointer __node, const void* __c) _NOEXCEPT
        : __node_(__node)
        {
            (void)__c;
#ifdef _LIBCPP_ENABLE_DEBUG_MODE
            __get_db()->__insert_ic(this, __c);
#endif
        }
    template <class, class, class, class> friend class __hash_table;
    template <class> friend class _LIBCPP_TEMPLATE_VIS __hash_map_const_iterator;
    template <class, class, class, class, class> friend class _LIBCPP_TEMPLATE_VIS unordered_map;
    template <class, class, class, class, class> friend class _LIBCPP_TEMPLATE_VIS unordered_multimap;
};

template <class _NodePtr>
class _LIBCPP_TEMPLATE_VIS __hash_local_iterator
{
    typedef __hash_node_types<_NodePtr> _NodeTypes;
    typedef _NodePtr                            __node_pointer;
    typedef typename _NodeTypes::__next_pointer __next_pointer;

    __next_pointer         __node_;
    size_t                 __bucket_;
    size_t                 __bucket_count_;

public:
    typedef forward_iterator_tag                                iterator_category;
    typedef typename _NodeTypes::__node_value_type              value_type;
    typedef typename _NodeTypes::difference_type                difference_type;
    typedef value_type&                                         reference;
    typedef typename _NodeTypes::__node_value_type_pointer      pointer;

    _LIBCPP_INLINE_VISIBILITY __hash_local_iterator() _NOEXCEPT : __node_(nullptr) {
        _VSTD::__debug_db_insert_i(this);
    }

#ifdef _LIBCPP_ENABLE_DEBUG_MODE
    _LIBCPP_INLINE_VISIBILITY
    __hash_local_iterator(const __hash_local_iterator& __i)
        : __node_(__i.__node_),
          __bucket_(__i.__bucket_),
          __bucket_count_(__i.__bucket_count_)
    {
        __get_db()->__iterator_copy(this, _VSTD::addressof(__i));
    }

    _LIBCPP_INLINE_VISIBILITY
    ~__hash_local_iterator()
    {
        __get_db()->__erase_i(this);
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_local_iterator& operator=(const __hash_local_iterator& __i)
    {
        if (this != _VSTD::addressof(__i))
        {
            __get_db()->__iterator_copy(this, _VSTD::addressof(__i));
            __node_ = __i.__node_;
            __bucket_ = __i.__bucket_;
            __bucket_count_ = __i.__bucket_count_;
        }
        return *this;
    }
#endif // _LIBCPP_ENABLE_DEBUG_MODE

    _LIBCPP_INLINE_VISIBILITY
    reference operator*() const {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                           "Attempted to dereference a non-dereferenceable unordered container local_iterator");
        return __node_->__upcast()->__value_;
    }

    _LIBCPP_INLINE_VISIBILITY
    pointer operator->() const {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                             "Attempted to dereference a non-dereferenceable unordered container local_iterator");
        return pointer_traits<pointer>::pointer_to(__node_->__upcast()->__value_);
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_local_iterator& operator++() {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                       "Attempted to increment a non-incrementable unordered container local_iterator");
        __node_ = __node_->__next_;
        if (__node_ != nullptr && std::__constrain_hash(__node_->__hash(), __bucket_count_) != __bucket_)
            __node_ = nullptr;
        return *this;
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_local_iterator operator++(int)
    {
        __hash_local_iterator __t(*this);
        ++(*this);
        return __t;
    }

    friend _LIBCPP_INLINE_VISIBILITY
    bool operator==(const __hash_local_iterator& __x, const __hash_local_iterator& __y)
    {
        return __x.__node_ == __y.__node_;
    }
    friend _LIBCPP_INLINE_VISIBILITY
    bool operator!=(const __hash_local_iterator& __x, const __hash_local_iterator& __y)
        {return !(__x == __y);}

private:
    _LIBCPP_INLINE_VISIBILITY
    explicit __hash_local_iterator(__next_pointer __node, size_t __bucket,
                                   size_t __bucket_count, const void* __c) _NOEXCEPT
        : __node_(__node),
          __bucket_(__bucket),
          __bucket_count_(__bucket_count)
        {
            (void)__c;
#ifdef _LIBCPP_ENABLE_DEBUG_MODE
            __get_db()->__insert_ic(this, __c);
#endif
            if (__node_ != nullptr)
                __node_ = __node_->__next_;
        }
    template <class, class, class, class> friend class __hash_table;
    template <class> friend class _LIBCPP_TEMPLATE_VIS __hash_const_local_iterator;
    template <class> friend class _LIBCPP_TEMPLATE_VIS __hash_map_iterator;
};

template <class _ConstNodePtr>
class _LIBCPP_TEMPLATE_VIS __hash_const_local_iterator
{
    typedef __hash_node_types<_ConstNodePtr> _NodeTypes;
    typedef _ConstNodePtr                       __node_pointer;
    typedef typename _NodeTypes::__next_pointer __next_pointer;

    __next_pointer         __node_;
    size_t                 __bucket_;
    size_t                 __bucket_count_;

    typedef pointer_traits<__node_pointer>          __pointer_traits;
    typedef typename __pointer_traits::element_type __node;
    typedef __remove_const_t<__node>                  __non_const_node;
    typedef __rebind_pointer_t<__node_pointer, __non_const_node>
        __non_const_node_pointer;
public:
    typedef __hash_local_iterator<__non_const_node_pointer>
                                                    __non_const_iterator;

    typedef forward_iterator_tag                                 iterator_category;
    typedef typename _NodeTypes::__node_value_type               value_type;
    typedef typename _NodeTypes::difference_type                 difference_type;
    typedef const value_type&                                    reference;
    typedef typename _NodeTypes::__const_node_value_type_pointer pointer;


    _LIBCPP_INLINE_VISIBILITY __hash_const_local_iterator() _NOEXCEPT : __node_(nullptr) {
        _VSTD::__debug_db_insert_i(this);
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_const_local_iterator(const __non_const_iterator& __x) _NOEXCEPT
        : __node_(__x.__node_),
          __bucket_(__x.__bucket_),
          __bucket_count_(__x.__bucket_count_)
    {
#ifdef _LIBCPP_ENABLE_DEBUG_MODE
        __get_db()->__iterator_copy(this, _VSTD::addressof(__x));
#endif
    }

#ifdef _LIBCPP_ENABLE_DEBUG_MODE
    _LIBCPP_INLINE_VISIBILITY
    __hash_const_local_iterator(const __hash_const_local_iterator& __i)
        : __node_(__i.__node_),
          __bucket_(__i.__bucket_),
          __bucket_count_(__i.__bucket_count_)
    {
        __get_db()->__iterator_copy(this, _VSTD::addressof(__i));
    }

    _LIBCPP_INLINE_VISIBILITY
    ~__hash_const_local_iterator()
    {
        __get_db()->__erase_i(this);
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_const_local_iterator& operator=(const __hash_const_local_iterator& __i)
    {
        if (this != _VSTD::addressof(__i))
        {
            __get_db()->__iterator_copy(this, _VSTD::addressof(__i));
            __node_ = __i.__node_;
            __bucket_ = __i.__bucket_;
            __bucket_count_ = __i.__bucket_count_;
        }
        return *this;
    }
#endif // _LIBCPP_ENABLE_DEBUG_MODE

    _LIBCPP_INLINE_VISIBILITY
    reference operator*() const {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                           "Attempted to dereference a non-dereferenceable unordered container const_local_iterator");
        return __node_->__upcast()->__value_;
    }

    _LIBCPP_INLINE_VISIBILITY
    pointer operator->() const {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                           "Attempted to dereference a non-dereferenceable unordered container const_local_iterator");
        return pointer_traits<pointer>::pointer_to(__node_->__upcast()->__value_);
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_const_local_iterator& operator++() {
        _LIBCPP_DEBUG_ASSERT(__get_const_db()->__dereferenceable(this),
                       "Attempted to increment a non-incrementable unordered container const_local_iterator");
        __node_ = __node_->__next_;
        if (__node_ != nullptr && std::__constrain_hash(__node_->__hash(), __bucket_count_) != __bucket_)
            __node_ = nullptr;
        return *this;
    }

    _LIBCPP_INLINE_VISIBILITY
    __hash_const_local_iterator operator++(int)
    {
        __hash_const_local_iterator __t(*this);
        ++(*this);
        return __t;
    }

    friend _LIBCPP_INLINE_VISIBILITY
    bool operator==(const __hash_const_local_iterator& __x, const __hash_const_local_iterator& __y)
    {
        return __x.__node_ == __y.__node_;
    }
    friend _LIBCPP_INLINE_VISIBILITY
    bool operator!=(const __hash_const_local_iterator& __x, const __hash_const_local_iterator& __y)
        {return !(__x == __y);}

private:
    _LIBCPP_INLINE_VISIBILITY
    explicit __hash_const_local_iterator(__next_pointer __node_ptr, size_t __bucket,
                                         size_t __bucket_count, const void* __c) _NOEXCEPT
        : __node_(__node_ptr),
          __bucket_(__bucket),
          __bucket_count_(__bucket_count)
        {
            (void)__c;
#ifdef _LIBCPP_ENABLE_DEBUG_MODE
            __get_db()->__insert_ic(this, __c);
#endif
            if (__node_ != nullptr)
                __node_ = __node_->__next_;
        }
    template <class, class, class, class> friend class __hash_table;
    template <class> friend class _LIBCPP_TEMPLATE_VIS __hash_map_const_iterator;
};

template <class _Alloc>
class __bucket_list_deallocator
{
    typedef _Alloc                                          allocator_type;
    typedef allocator_traits<allocator_type>                __alloc_traits;
    typedef typename __alloc_traits::size_type              size_type;

    __compressed_pair<size_type, allocator_type> __data_;
public:
    typedef typename __alloc_traits::pointer pointer;

    _LIBCPP_INLINE_VISIBILITY
    __bucket_list_deallocator()
        _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value)
        : __data_(0, __default_init_tag()) {}

    _LIBCPP_INLINE_VISIBILITY
    __bucket_list_deallocator(const allocator_type& __a, size_type __size)
        _NOEXCEPT_(is_nothrow_copy_constructible<allocator_type>::value)
        : __data_(__size, __a) {}

    _LIBCPP_INLINE_VISIBILITY
    __bucket_list_deallocator(__bucket_list_deallocator&& __x)
        _NOEXCEPT_(is_nothrow_move_constructible<allocator_type>::value)
        : __data_(_VSTD::move(__x.__data_))
    {
        __x.size() = 0;
    }

    _LIBCPP_INLINE_VISIBILITY
    size_type& size() _NOEXCEPT {return __data_.first();}
    _LIBCPP_INLINE_VISIBILITY
    size_type  size() const _NOEXCEPT {return __data_.first();}

    _LIBCPP_INLINE_VISIBILITY
    allocator_type& __alloc() _NOEXCEPT {return __data_.second();}
    _LIBCPP_INLINE_VISIBILITY
    const allocator_type& __alloc() const _NOEXCEPT {return __data_.second();}

    _LIBCPP_INLINE_VISIBILITY
    void operator()(pointer __p) _NOEXCEPT
    {
        __alloc_traits::deallocate(__alloc(), __p, size());
    }
};

template <class _Alloc> class __hash_map_node_destructor;

template <class _Alloc>
class __hash_node_destructor
{
    typedef _Alloc                                          allocator_type;
    typedef allocator_traits<allocator_type>                __alloc_traits;

public:
    typedef typename __alloc_traits::pointer                pointer;
private:
    typedef __hash_node_types<pointer> _NodeTypes;

    allocator_type& __na_;

public:
    bool __value_constructed;

    __hash_node_destructor(__hash_node_destructor const&) = default;
    __hash_node_destructor& operator=(const __hash_node_destructor&) = delete;


    _LIBCPP_INLINE_VISIBILITY
    explicit __hash_node_destructor(allocator_type& __na,
                                    bool __constructed = false) _NOEXCEPT
        : __na_(__na),
          __value_constructed(__constructed)
        {}

    _LIBCPP_INLINE_VISIBILITY
    void operator()(pointer __p) _NOEXCEPT
    {
        if (__value_constructed)
            __alloc_traits::destroy(__na_, _NodeTypes::__get_ptr(__p->__value_));
        if (__p)
            __alloc_traits::deallocate(__na_, __p, 1);
    }

    template <class> friend class __hash_map_node_destructor;
};

#if _LIBCPP_STD_VER > 14
template <class _NodeType, class _Alloc>
struct __generic_container_node_destructor;

template <class _Tp, class _VoidPtr, class _Alloc>
struct __generic_container_node_destructor<__hash_node<_Tp, _VoidPtr>, _Alloc>
    : __hash_node_destructor<_Alloc>
{
    using __hash_node_destructor<_Alloc>::__hash_node_destructor;
};
#endif

template <class _Key, class _Hash, class _Equal>
struct __enforce_unordered_container_requirements {
#ifndef _LIBCPP_CXX03_LANG
    static_assert(__check_hash_requirements<_Key, _Hash>::value,
    "the specified hash does not meet the Hash requirements");
    static_assert(is_copy_constructible<_Equal>::value,
    "the specified comparator is required to be copy constructible");
#endif
    typedef int type;
};

template <class _Key, class _Hash, class _Equal>
#ifndef _LIBCPP_CXX03_LANG
    _LIBCPP_DIAGNOSE_WARNING(!__invokable<_Equal const&, _Key const&, _Key const&>::value,
    "the specified comparator type does not provide a viable const call operator")
    _LIBCPP_DIAGNOSE_WARNING(!__invokable<_Hash const&, _Key const&>::value,
    "the specified hash functor does not provide a viable const call operator")
#endif
typename __enforce_unordered_container_requirements<_Key, _Hash, _Equal>::type
__diagnose_unordered_container_requirements(int);

// This dummy overload is used so that the compiler won't emit a spurious
// "no matching function for call to __diagnose_unordered_xxx" diagnostic
// when the overload above causes a hard error.
template <class _Key, class _Hash, class _Equal>
int __diagnose_unordered_container_requirements(void*);

template <class _Tp, class _Hash, class _Equal, class _Alloc>
class __hash_table
{
public:
    typedef _Tp    value_type;
    typedef _Hash  hasher;
    typedef _Equal key_equal;
    typedef _Alloc allocator_type;

private:
    typedef allocator_traits<allocator_type> __alloc_traits;
    typedef typename
      __make_hash_node_types<value_type, typename __alloc_traits::void_pointer>::type
                                                                     _NodeTypes;
public:

    typedef typename _NodeTypes::__node_value_type           __node_value_type;
    typedef typename _NodeTypes::__container_value_type      __container_value_type;
    typedef typename _NodeTypes::key_type                    key_type;
    typedef value_type&                              reference;
    typedef const value_type&                        const_reference;
    typedef typename __alloc_traits::pointer         pointer;
    typedef typename __alloc_traits::const_pointer   const_pointer;
#ifndef _LIBCPP_ABI_FIX_UNORDERED_CONTAINER_SIZE_TYPE
    typedef typename __alloc_traits::size_type       size_type;
#else
    typedef typename _NodeTypes::size_type           size_type;
#endif
    typedef typename _NodeTypes::difference_type     difference_type;
public:
    // Create __node

    typedef typename _NodeTypes::__node_type __node;
    typedef __rebind_alloc<__alloc_traits, __node>   __node_allocator;
    typedef allocator_traits<__node_allocator>       __node_traits;
    typedef typename _NodeTypes::__void_pointer      __void_pointer;
    typedef typename _NodeTypes::__node_pointer      __node_pointer;
    typedef typename _NodeTypes::__node_pointer      __node_const_pointer;
    typedef typename _NodeTypes::__node_base_type    __first_node;
    typedef typename _NodeTypes::__node_base_pointer __node_base_pointer;
    typedef typename _NodeTypes::__next_pointer      __next_pointer;

private:
    // check for sane allocator pointer rebinding semantics. Rebinding the
    // allocator for a new pointer type should be exactly the same as rebinding
    // the pointer using 'pointer_traits'.
    static_assert((is_same<__node_pointer, typename __node_traits::pointer>::value),
                  "Allocator does not rebind pointers in a sane manner.");
    typedef __rebind_alloc<__node_traits, __first_node> __node_base_allocator;
    typedef allocator_traits<__node_base_allocator> __node_base_traits;
    static_assert((is_same<__node_base_pointer, typename __node_base_traits::pointer>::value),
                 "Allocator does not rebind pointers in a sane manner.");

private:

    typedef __rebind_alloc<__node_traits, __next_pointer>  __pointer_allocator;
    typedef __bucket_list_deallocator<__pointer_allocator> __bucket_list_deleter;
    typedef unique_ptr<__next_pointer[], __bucket_list_deleter> __bucket_list;
    typedef allocator_traits<__pointer_allocator>          __pointer_alloc_traits;
    typedef typename __bucket_list_deleter::pointer       __node_pointer_pointer;

    // --- Member data begin ---
    __bucket_list                                         __bucket_list_;
    __compressed_pair<__first_node, __node_allocator>     __p1_;
    __compressed_pair<size_type, hasher>                  __p2_;
    __compressed_pair<float, key_equal>                   __p3_;
    // --- Member data end ---

    _LIBCPP_INLINE_VISIBILITY
    size_type& size() _NOEXCEPT {return __p2_.first();}
public:
    _LIBCPP_INLINE_VISIBILITY
    size_type  size() const _NOEXCEPT {return __p2_.first();}

    _LIBCPP_INLINE_VISIBILITY
    hasher& hash_function() _NOEXCEPT {return __p2_.second();}
    _LIBCPP_INLINE_VISIBILITY
    const hasher& hash_function() const _NOEXCEPT {return __p2_.second();}

    _LIBCPP_INLINE_VISIBILITY
    float& max_load_factor() _NOEXCEPT {return __p3_.first();}
    _LIBCPP_INLINE_VISIBILITY
    float  max_load_factor() const _NOEXCEPT {return __p3_.first();}

    _LIBCPP_INLINE_VISIBILITY
    key_equal& key_eq() _NOEXCEPT {return __p3_.second();}
    _LIBCPP_INLINE_VISIBILITY
    const key_equal& key_eq() const _NOEXCEPT {return __p3_.second();}

    _LIBCPP_INLINE_VISIBILITY
    __node_allocator& __node_alloc() _NOEXCEPT {return __p1_.second();}
    _LIBCPP_INLINE_VISIBILITY
    const __node_allocator& __node_alloc() const _NOEXCEPT
        {return __p1_.second();}

public:
    typedef __hash_iterator<__node_pointer>                   iterator;
    typedef __hash_const_iterator<__node_pointer>             const_iterator;
    typedef __hash_local_iterator<__node_pointer>             local_iterator;
    typedef __hash_const_local_iterator<__node_pointer>       const_local_iterator;

    _LIBCPP_INLINE_VISIBILITY
    __hash_table()
        _NOEXCEPT_(
            is_nothrow_default_constructible<__bucket_list>::value &&
            is_nothrow_default_constructible<__first_node>::value &&
            is_nothrow_default_constructible<__node_allocator>::value &&
            is_nothrow_default_constructible<hasher>::value &&
            is_nothrow_default_constructible<key_equal>::value);
    _LIBCPP_INLINE_VISIBILITY
    __hash_table(const hasher& __hf, const key_equal& __eql);
    __hash_table(const hasher& __hf, const key_equal& __eql,
                 const allocator_type& __a);
    explicit __hash_table(const allocator_type& __a);
    __hash_table(const __hash_table& __u);
    __hash_table(const __hash_table& __u, const allocator_type& __a);
    __hash_table(__hash_table&& __u)
        _NOEXCEPT_(
            is_nothrow_move_constructible<__bucket_list>::value &&
            is_nothrow_move_constructible<__first_node>::value &&
            is_nothrow_move_constructible<__node_allocator>::value &&
            is_nothrow_move_constructible<hasher>::value &&
            is_nothrow_move_constructible<key_equal>::value);
    __hash_table(__hash_table&& __u, const allocator_type& __a);
    ~__hash_table();

    __hash_table& operator=(const __hash_table& __u);
    _LIBCPP_INLINE_VISIBILITY
    __hash_table& operator=(__hash_table&& __u)
        _NOEXCEPT_(
            __node_traits::propagate_on_container_move_assignment::value &&
            is_nothrow_move_assignable<__node_allocator>::value &&
            is_nothrow_move_assignable<hasher>::value &&
            is_nothrow_move_assignable<key_equal>::value);
    template <class _InputIterator>
        void __assign_unique(_InputIterator __first, _InputIterator __last);
    template <class _InputIterator>
        void __assign_multi(_InputIterator __first, _InputIterator __last);

    _LIBCPP_INLINE_VISIBILITY
    size_type max_size() const _NOEXCEPT
    {
        return _VSTD::min<size_type>(
            __node_traits::max_size(__node_alloc()),
            numeric_limits<difference_type >::max()
        );
    }

private:
    _LIBCPP_INLINE_VISIBILITY
    __next_pointer __node_insert_multi_prepare(size_t __cp_hash,
                                               value_type& __cp_val);
    _LIBCPP_INLINE_VISIBILITY
    void __node_insert_multi_perform(__node_pointer __cp,
                                     __next_pointer __pn) _NOEXCEPT;

    _LIBCPP_INLINE_VISIBILITY
    __next_pointer __node_insert_unique_prepare(size_t __nd_hash,
                                                value_type& __nd_val);
    _LIBCPP_INLINE_VISIBILITY
    void __node_insert_unique_perform(__node_pointer __ptr) _NOEXCEPT;

public:
    _LIBCPP_INLINE_VISIBILITY
    pair<iterator, bool> __node_insert_unique(__node_pointer __nd);
    _LIBCPP_INLINE_VISIBILITY
    iterator             __node_insert_multi(__node_pointer __nd);
    _LIBCPP_INLINE_VISIBILITY
    iterator             __node_insert_multi(const_iterator __p,
                                             __node_pointer __nd);

    template <class _Key, class ..._Args>
    _LIBCPP_INLINE_VISIBILITY
    pair<iterator, bool> __emplace_unique_key_args(_Key const& __k, _Args&&... __args);

    template <class... _Args>
    _LIBCPP_INLINE_VISIBILITY
    pair<iterator, bool> __emplace_unique_impl(_Args&&... __args);

    template <class _Pp>
    _LIBCPP_INLINE_VISIBILITY
    pair<iterator, bool> __emplace_unique(_Pp&& __x) {
      return __emplace_unique_extract_key(_VSTD::forward<_Pp>(__x),
                                          __can_extract_key<_Pp, key_type>());
    }

    template <class _First, class _Second>
    _LIBCPP_INLINE_VISIBILITY
    __enable_if_t<__can_extract_map_key<_First, key_type, __container_value_type>::value, pair<iterator, bool> >
    __emplace_unique(_First&& __f, _Second&& __s) {
        return __emplace_unique_key_args(__f, _VSTD::forward<_First>(__f),
                                              _VSTD::forward<_Second>(__s));
    }

    template <class... _Args>
    _LIBCPP_INLINE_VISIBILITY
    pair<iterator, bool> __emplace_unique(_Args&&... __args) {
      return __emplace_unique_impl(_VSTD::forward<_Args>(__args)...);
    }

    template <class _Pp>
    _LIBCPP_INLINE_VISIBILITY
    pair<iterator, bool>
    __emplace_unique_extract_key(_Pp&& __x, __extract_key_fail_tag) {
      return __emplace_unique_impl(_VSTD::forward<_Pp>(__x));
    }
    template <class _Pp>
    _LIBCPP_INLINE_VISIBILITY
    pair<iterator, bool>
    __emplace_unique_extract_key(_Pp&& __x, __extract_key_self_tag) {
      return __emplace_unique_key_args(__x, _VSTD::forward<_Pp>(__x));
    }
    template <class _Pp>
    _LIBCPP_INLINE_VISIBILITY
    pair<iterator, bool>
    __emplace_unique_extract_key(_Pp&& __x, __extract_key_first_tag) {
      return __emplace_unique_key_args(__x.first, _VSTD::forward<_Pp>(__x));
    }

    template <class... _Args>
    _LIBCPP_INLINE_VISIBILITY
    iterator __emplace_multi(_Args&&... __args);
    template <class... _Args>
    _LIBCPP_INLINE_VISIBILITY
    iterator __emplace_hint_multi(const_iterator __p, _Args&&... __args);


    _LIBCPP_INLINE_VISIBILITY
    pair<iterator, bool>
    __insert_unique(__container_value_type&& __x) {
      return __emplace_unique_key_args(_NodeTypes::__get_key(__x), _VSTD::move(__x));
    }

    template <class _Pp, class = __enable_if_t<!__is_same_uncvref<_Pp, __container_value_type>::value> >
    _LIBCPP_INLINE_VISIBILITY
    pair<iterator, bool> __insert_unique(_Pp&& __x) {
      return __emplace_unique(_VSTD::forward<_Pp>(__x));
    }

    template <class _Pp>
    _LIBCPP_INLINE_VISIBILITY
    iterator __insert_multi(_Pp&& __x) {
      return __emplace_multi(_VSTD::forward<_Pp>(__x));
    }

    template <class _Pp>
    _LIBCPP_INLINE_VISIBILITY
    iterator __insert_multi(const_iterator __p, _Pp&& __x) {
        return __emplace_hint_multi(__p, _VSTD::forward<_Pp>(__x));
    }

    _LIBCPP_INLINE_VISIBILITY
    pair<iterator, bool> __insert_unique(const __container_value_type& __x) {
        return __emplace_unique_key_args(_NodeTypes::__get_key(__x), __x);
    }

#if _LIBCPP_STD_VER > 14
    template <class _NodeHandle, class _InsertReturnType>
    _LIBCPP_INLINE_VISIBILITY
    _InsertReturnType __node_handle_insert_unique(_NodeHandle&& __nh);
    template <class _NodeHandle>
    _LIBCPP_INLINE_VISIBILITY
    iterator __node_handle_insert_unique(const_iterator __hint,
                                         _NodeHandle&& __nh);
    template <class _Table>
    _LIBCPP_INLINE_VISIBILITY
    void __node_handle_merge_unique(_Table& __source);

    template <class _NodeHandle>
    _LIBCPP_INLINE_VISIBILITY
    iterator __node_handle_insert_multi(_NodeHandle&& __nh);
    template <class _NodeHandle>
    _LIBCPP_INLINE_VISIBILITY
    iterator __node_handle_insert_multi(const_iterator __hint, _NodeHandle&& __nh);
    template <class _Table>
    _LIBCPP_INLINE_VISIBILITY
    void __node_handle_merge_multi(_Table& __source);

    template <class _NodeHandle>
    _LIBCPP_INLINE_VISIBILITY
    _NodeHandle __node_handle_extract(key_type const& __key);
    template <class _NodeHandle>
    _LIBCPP_INLINE_VISIBILITY
    _NodeHandle __node_handle_extract(const_iterator __it);
#endif

    void clear() _NOEXCEPT;
    _LIBCPP_INLINE_VISIBILITY void __rehash_unique(size_type __n) { __rehash<true>(__n); }
    _LIBCPP_INLINE_VISIBILITY void __rehash_multi(size_type __n) { __rehash<false>(__n); }
    _LIBCPP_INLINE_VISIBILITY void __reserve_unique(size_type __n)
    {
        __rehash_unique(static_cast<size_type>(std::ceil(__n / max_load_factor())));
    }
    _LIBCPP_INLINE_VISIBILITY void __reserve_multi(size_type __n)
    {
        __rehash_multi(static_cast<size_type>(std::ceil(__n / max_load_factor())));
    }

    _LIBCPP_INLINE_VISIBILITY
    size_type bucket_count() const _NOEXCEPT
    {
        return __bucket_list_.get_deleter().size();
    }

    _LIBCPP_INLINE_VISIBILITY
    iterator       begin() _NOEXCEPT;
    _LIBCPP_INLINE_VISIBILITY
    iterator       end() _NOEXCEPT;
    _LIBCPP_INLINE_VISIBILITY
    const_iterator begin() const _NOEXCEPT;
    _LIBCPP_INLINE_VISIBILITY
    const_iterator end() const _NOEXCEPT;

    template <class _Key>
        _LIBCPP_INLINE_VISIBILITY
        size_type bucket(const _Key& __k) const
        {
            _LIBCPP_ASSERT(bucket_count() > 0,
                "unordered container::bucket(key) called when bucket_count() == 0");
            return std::__constrain_hash(hash_function()(__k), bucket_count());
        }

    template <class _Key>
        iterator       find(const _Key& __x);
    template <class _Key>
        const_iterator find(const _Key& __x) const;

    typedef __hash_node_destructor<__node_allocator> _Dp;
    typedef unique_ptr<__node, _Dp> __node_holder;

    iterator erase(const_iterator __p);
    iterator erase(const_iterator __first, const_iterator __last);
    template <class _Key>
        size_type __erase_unique(const _Key& __k);
    template <class _Key>
        size_type __erase_multi(const _Key& __k);
    __node_holder remove(const_iterator __p) _NOEXCEPT;

    template <class _Key>
        _LIBCPP_INLINE_VISIBILITY
        size_type __count_unique(const _Key& __k) const;
    template <class _Key>
        size_type __count_multi(const _Key& __k) const;

    template <class _Key>
        pair<iterator, iterator>
        __equal_range_unique(const _Key& __k);
    template <class _Key>
        pair<const_iterator, const_iterator>
        __equal_range_unique(const _Key& __k) const;

    template <class _Key>
        pair<iterator, iterator>
        __equal_range_multi(const _Key& __k);
    template <class _Key>
        pair<const_iterator, const_iterator>
        __equal_range_multi(const _Key& __k) const;

    void swap(__hash_table& __u)
#if _LIBCPP_STD_VER <= 11
        _NOEXCEPT_(
            __is_nothrow_swappable<hasher>::value && __is_nothrow_swappable<key_equal>::value
            && (!allocator_traits<__pointer_allocator>::propagate_on_container_swap::value
                  || __is_nothrow_swappable<__pointer_allocator>::value)
            && (!__node_traits::propagate_on_container_swap::value
                  || __is_nothrow_swappable<__node_allocator>::value)
            );
#else
     _NOEXCEPT_(__is_nothrow_swappable<hasher>::value && __is_nothrow_swappable<key_equal>::value);
#endif

    _LIBCPP_INLINE_VISIBILITY
    size_type max_bucket_count() const _NOEXCEPT
        {return max_size(); }
    size_type bucket_size(size_type __n) const;
    _LIBCPP_INLINE_VISIBILITY float load_factor() const _NOEXCEPT
    {
        size_type __bc = bucket_count();
        return __bc != 0 ? (float)size() / __bc : 0.f;
    }
    _LIBCPP_INLINE_VISIBILITY void max_load_factor(float __mlf) _NOEXCEPT
    {
        _LIBCPP_ASSERT(__mlf > 0,
            "unordered container::max_load_factor(lf) called with lf <= 0");
        max_load_factor() = _VSTD::max(__mlf, load_factor());
    }

    _LIBCPP_INLINE_VISIBILITY
    local_iterator
    begin(size_type __n)
    {
        _LIBCPP_ASSERT(__n < bucket_count(),
            "unordered container::begin(n) called with n >= bucket_count()");
        return local_iterator(__bucket_list_[__n], __n, bucket_count(), this);
    }

    _LIBCPP_INLINE_VISIBILITY
    local_iterator
    end(size_type __n)
    {
        _LIBCPP_ASSERT(__n < bucket_count(),
            "unordered container::end(n) called with n >= bucket_count()");
        return local_iterator(nullptr, __n, bucket_count(), this);
    }

    _LIBCPP_INLINE_VISIBILITY
    const_local_iterator
    cbegin(size_type __n) const
    {
        _LIBCPP_ASSERT(__n < bucket_count(),
            "unordered container::cbegin(n) called with n >= bucket_count()");
        return const_local_iterator(__bucket_list_[__n], __n, bucket_count(), this);
    }

    _LIBCPP_INLINE_VISIBILITY
    const_local_iterator
    cend(size_type __n) const
    {
        _LIBCPP_ASSERT(__n < bucket_count(),
            "unordered container::cend(n) called with n >= bucket_count()");
        return const_local_iterator(nullptr, __n, bucket_count(), this);
    }

#ifdef _LIBCPP_ENABLE_DEBUG_MODE

    bool __dereferenceable(const const_iterator* __i) const;
    bool __decrementable(const const_iterator* __i) const;
    bool __addable(const const_iterator* __i, ptrdiff_t __n) const;
    bool __subscriptable(const const_iterator* __i, ptrdiff_t __n) const;

#endif // _LIBCPP_ENABLE_DEBUG_MODE

private:
    template <bool _UniqueKeys> void __rehash(size_type __n);
    template <bool _UniqueKeys> void __do_rehash(size_type __n);

    template <class ..._Args>
    __node_holder __construct_node(_Args&& ...__args);

    template <class _First, class ..._Rest>
    __node_holder __construct_node_hash(size_t __hash, _First&& __f, _Rest&&... __rest);


    _LIBCPP_INLINE_VISIBILITY
    void __copy_assign_alloc(const __hash_table& __u)
        {__copy_assign_alloc(__u, integral_constant<bool,
             __node_traits::propagate_on_container_copy_assignment::value>());}
    void __copy_assign_alloc(const __hash_table& __u, true_type);
    _LIBCPP_INLINE_VISIBILITY
        void __copy_assign_alloc(const __hash_table&, false_type) {}

    void __move_assign(__hash_table& __u, false_type);
    void __move_assign(__hash_table& __u, true_type)
        _NOEXCEPT_(
            is_nothrow_move_assignable<__node_allocator>::value &&
            is_nothrow_move_assignable<hasher>::value &&
            is_nothrow_move_assignable<key_equal>::value);
    _LIBCPP_INLINE_VISIBILITY
    void __move_assign_alloc(__hash_table& __u)
        _NOEXCEPT_(
            !__node_traits::propagate_on_container_move_assignment::value ||
            (is_nothrow_move_assignable<__pointer_allocator>::value &&
             is_nothrow_move_assignable<__node_allocator>::value))
        {__move_assign_alloc(__u, integral_constant<bool,
             __node_traits::propagate_on_container_move_assignment::value>());}
    _LIBCPP_INLINE_VISIBILITY
    void __move_assign_alloc(__hash_table& __u, true_type)
        _NOEXCEPT_(
            is_nothrow_move_assignable<__pointer_allocator>::value &&
            is_nothrow_move_assignable<__node_allocator>::value)
    {
        __bucket_list_.get_deleter().__alloc() =
                _VSTD::move(__u.__bucket_list_.get_deleter().__alloc());
        __node_alloc() = _VSTD::move(__u.__node_alloc());
    }
    _LIBCPP_INLINE_VISIBILITY
        void __move_assign_alloc(__hash_table&, false_type) _NOEXCEPT {}

    void __deallocate_node(__next_pointer __np) _NOEXCEPT;
    __next_pointer __detach() _NOEXCEPT;

    template <class, class, class, class, class> friend class _LIBCPP_TEMPLATE_VIS unordered_map;
    template <class, class, class, class, class> friend class _LIBCPP_TEMPLATE_VIS unordered_multimap;
};

template <class _Tp, class _Hash, class _Equal, class _Alloc>
inline
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__hash_table()
    _NOEXCEPT_(
        is_nothrow_default_constructible<__bucket_list>::value &&
        is_nothrow_default_constructible<__first_node>::value &&
        is_nothrow_default_constructible<__node_allocator>::value &&
        is_nothrow_default_constructible<hasher>::value &&
        is_nothrow_default_constructible<key_equal>::value)
    : __p2_(0, __default_init_tag()),
      __p3_(1.0f, __default_init_tag())
{
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
inline
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__hash_table(const hasher& __hf,
                                                       const key_equal& __eql)
    : __bucket_list_(nullptr, __bucket_list_deleter()),
      __p1_(),
      __p2_(0, __hf),
      __p3_(1.0f, __eql)
{
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__hash_table(const hasher& __hf,
                                                       const key_equal& __eql,
                                                       const allocator_type& __a)
    : __bucket_list_(nullptr, __bucket_list_deleter(__pointer_allocator(__a), 0)),
      __p1_(__default_init_tag(), __node_allocator(__a)),
      __p2_(0, __hf),
      __p3_(1.0f, __eql)
{
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__hash_table(const allocator_type& __a)
    : __bucket_list_(nullptr, __bucket_list_deleter(__pointer_allocator(__a), 0)),
      __p1_(__default_init_tag(), __node_allocator(__a)),
      __p2_(0, __default_init_tag()),
      __p3_(1.0f, __default_init_tag())
{
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__hash_table(const __hash_table& __u)
    : __bucket_list_(nullptr,
          __bucket_list_deleter(allocator_traits<__pointer_allocator>::
              select_on_container_copy_construction(
                  __u.__bucket_list_.get_deleter().__alloc()), 0)),
      __p1_(__default_init_tag(), allocator_traits<__node_allocator>::
          select_on_container_copy_construction(__u.__node_alloc())),
      __p2_(0, __u.hash_function()),
      __p3_(__u.__p3_)
{
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__hash_table(const __hash_table& __u,
                                                       const allocator_type& __a)
    : __bucket_list_(nullptr, __bucket_list_deleter(__pointer_allocator(__a), 0)),
      __p1_(__default_init_tag(), __node_allocator(__a)),
      __p2_(0, __u.hash_function()),
      __p3_(__u.__p3_)
{
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__hash_table(__hash_table&& __u)
        _NOEXCEPT_(
            is_nothrow_move_constructible<__bucket_list>::value &&
            is_nothrow_move_constructible<__first_node>::value &&
            is_nothrow_move_constructible<__node_allocator>::value &&
            is_nothrow_move_constructible<hasher>::value &&
            is_nothrow_move_constructible<key_equal>::value)
    : __bucket_list_(_VSTD::move(__u.__bucket_list_)),
      __p1_(_VSTD::move(__u.__p1_)),
      __p2_(_VSTD::move(__u.__p2_)),
      __p3_(_VSTD::move(__u.__p3_))
{
    if (size() > 0)
    {
        __bucket_list_[std::__constrain_hash(__p1_.first().__next_->__hash(), bucket_count())] =
            __p1_.first().__ptr();
        __u.__p1_.first().__next_ = nullptr;
        __u.size() = 0;
    }
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__hash_table(__hash_table&& __u,
                                                       const allocator_type& __a)
    : __bucket_list_(nullptr, __bucket_list_deleter(__pointer_allocator(__a), 0)),
      __p1_(__default_init_tag(), __node_allocator(__a)),
      __p2_(0, _VSTD::move(__u.hash_function())),
      __p3_(_VSTD::move(__u.__p3_))
{
    if (__a == allocator_type(__u.__node_alloc()))
    {
        __bucket_list_.reset(__u.__bucket_list_.release());
        __bucket_list_.get_deleter().size() = __u.__bucket_list_.get_deleter().size();
        __u.__bucket_list_.get_deleter().size() = 0;
        if (__u.size() > 0)
        {
            __p1_.first().__next_ = __u.__p1_.first().__next_;
            __u.__p1_.first().__next_ = nullptr;
            __bucket_list_[std::__constrain_hash(__p1_.first().__next_->__hash(), bucket_count())] =
                __p1_.first().__ptr();
            size() = __u.size();
            __u.size() = 0;
        }
    }
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::~__hash_table()
{
#if defined(_LIBCPP_CXX03_LANG)
    static_assert((is_copy_constructible<key_equal>::value),
                 "Predicate must be copy-constructible.");
    static_assert((is_copy_constructible<hasher>::value),
                 "Hasher must be copy-constructible.");
#endif

    __deallocate_node(__p1_.first().__next_);
    std::__debug_db_erase_c(this);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__copy_assign_alloc(
        const __hash_table& __u, true_type)
{
    if (__node_alloc() != __u.__node_alloc())
    {
        clear();
        __bucket_list_.reset();
        __bucket_list_.get_deleter().size() = 0;
    }
    __bucket_list_.get_deleter().__alloc() = __u.__bucket_list_.get_deleter().__alloc();
    __node_alloc() = __u.__node_alloc();
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
__hash_table<_Tp, _Hash, _Equal, _Alloc>&
__hash_table<_Tp, _Hash, _Equal, _Alloc>::operator=(const __hash_table& __u)
{
    if (this != _VSTD::addressof(__u))
    {
        __copy_assign_alloc(__u);
        hash_function() = __u.hash_function();
        key_eq() = __u.key_eq();
        max_load_factor() = __u.max_load_factor();
        __assign_multi(__u.begin(), __u.end());
    }
    return *this;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__deallocate_node(__next_pointer __np)
    _NOEXCEPT
{
    __node_allocator& __na = __node_alloc();
    while (__np != nullptr)
    {
        __next_pointer __next = __np->__next_;
#ifdef _LIBCPP_ENABLE_DEBUG_MODE
        __c_node* __c = __get_db()->__find_c_and_lock(this);
        for (__i_node** __p = __c->end_; __p != __c->beg_; )
        {
            --__p;
            iterator* __i = static_cast<iterator*>((*__p)->__i_);
            if (__i->__node_ == __np)
            {
                (*__p)->__c_ = nullptr;
                if (--__c->end_ != __p)
                    _VSTD::memmove(__p, __p+1, (__c->end_ - __p)*sizeof(__i_node*));
            }
        }
        __get_db()->unlock();
#endif
        __node_pointer __real_np = __np->__upcast();
        __node_traits::destroy(__na, _NodeTypes::__get_ptr(__real_np->__value_));
        __node_traits::deallocate(__na, __real_np, 1);
        __np = __next;
    }
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::__next_pointer
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__detach() _NOEXCEPT
{
    size_type __bc = bucket_count();
    for (size_type __i = 0; __i < __bc; ++__i)
        __bucket_list_[__i] = nullptr;
    size() = 0;
    __next_pointer __cache = __p1_.first().__next_;
    __p1_.first().__next_ = nullptr;
    return __cache;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__move_assign(
        __hash_table& __u, true_type)
    _NOEXCEPT_(
        is_nothrow_move_assignable<__node_allocator>::value &&
        is_nothrow_move_assignable<hasher>::value &&
        is_nothrow_move_assignable<key_equal>::value)
{
    clear();
    __bucket_list_.reset(__u.__bucket_list_.release());
    __bucket_list_.get_deleter().size() = __u.__bucket_list_.get_deleter().size();
    __u.__bucket_list_.get_deleter().size() = 0;
    __move_assign_alloc(__u);
    size() = __u.size();
    hash_function() = _VSTD::move(__u.hash_function());
    max_load_factor() = __u.max_load_factor();
    key_eq() = _VSTD::move(__u.key_eq());
    __p1_.first().__next_ = __u.__p1_.first().__next_;
    if (size() > 0)
    {
        __bucket_list_[std::__constrain_hash(__p1_.first().__next_->__hash(), bucket_count())] =
            __p1_.first().__ptr();
        __u.__p1_.first().__next_ = nullptr;
        __u.size() = 0;
    }
    std::__debug_db_swap(this, std::addressof(__u));
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__move_assign(
        __hash_table& __u, false_type)
{
    if (__node_alloc() == __u.__node_alloc())
        __move_assign(__u, true_type());
    else
    {
        hash_function() = _VSTD::move(__u.hash_function());
        key_eq() = _VSTD::move(__u.key_eq());
        max_load_factor() = __u.max_load_factor();
        if (bucket_count() != 0)
        {
            __next_pointer __cache = __detach();
#ifndef _LIBCPP_NO_EXCEPTIONS
            try
            {
#endif // _LIBCPP_NO_EXCEPTIONS
                const_iterator __i = __u.begin();
                while (__cache != nullptr && __u.size() != 0)
                {
                    __cache->__upcast()->__value_ =
                        _VSTD::move(__u.remove(__i++)->__value_);
                    __next_pointer __next = __cache->__next_;
                    __node_insert_multi(__cache->__upcast());
                    __cache = __next;
                }
#ifndef _LIBCPP_NO_EXCEPTIONS
            }
            catch (...)
            {
                __deallocate_node(__cache);
                throw;
            }
#endif // _LIBCPP_NO_EXCEPTIONS
            __deallocate_node(__cache);
        }
        const_iterator __i = __u.begin();
        while (__u.size() != 0)
        {
            __node_holder __h = __construct_node(_NodeTypes::__move(__u.remove(__i++)->__value_));
            __node_insert_multi(__h.get());
            __h.release();
        }
    }
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
inline
__hash_table<_Tp, _Hash, _Equal, _Alloc>&
__hash_table<_Tp, _Hash, _Equal, _Alloc>::operator=(__hash_table&& __u)
    _NOEXCEPT_(
        __node_traits::propagate_on_container_move_assignment::value &&
        is_nothrow_move_assignable<__node_allocator>::value &&
        is_nothrow_move_assignable<hasher>::value &&
        is_nothrow_move_assignable<key_equal>::value)
{
    __move_assign(__u, integral_constant<bool,
                  __node_traits::propagate_on_container_move_assignment::value>());
    return *this;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _InputIterator>
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__assign_unique(_InputIterator __first,
                                                          _InputIterator __last)
{
    typedef iterator_traits<_InputIterator> _ITraits;
    typedef typename _ITraits::value_type _ItValueType;
    static_assert((is_same<_ItValueType, __container_value_type>::value),
                  "__assign_unique may only be called with the containers value type");

    if (bucket_count() != 0)
    {
        __next_pointer __cache = __detach();
#ifndef _LIBCPP_NO_EXCEPTIONS
        try
        {
#endif // _LIBCPP_NO_EXCEPTIONS
            for (; __cache != nullptr && __first != __last; ++__first)
            {
                __cache->__upcast()->__value_ = *__first;
                __next_pointer __next = __cache->__next_;
                __node_insert_unique(__cache->__upcast());
                __cache = __next;
            }
#ifndef _LIBCPP_NO_EXCEPTIONS
        }
        catch (...)
        {
            __deallocate_node(__cache);
            throw;
        }
#endif // _LIBCPP_NO_EXCEPTIONS
        __deallocate_node(__cache);
    }
    for (; __first != __last; ++__first)
        __insert_unique(*__first);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _InputIterator>
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__assign_multi(_InputIterator __first,
                                                         _InputIterator __last)
{
    typedef iterator_traits<_InputIterator> _ITraits;
    typedef typename _ITraits::value_type _ItValueType;
    static_assert((is_same<_ItValueType, __container_value_type>::value ||
                  is_same<_ItValueType, __node_value_type>::value),
                  "__assign_multi may only be called with the containers value type"
                  " or the nodes value type");
    if (bucket_count() != 0)
    {
        __next_pointer __cache = __detach();
#ifndef _LIBCPP_NO_EXCEPTIONS
        try
        {
#endif // _LIBCPP_NO_EXCEPTIONS
            for (; __cache != nullptr && __first != __last; ++__first)
            {
                __cache->__upcast()->__value_ = *__first;
                __next_pointer __next = __cache->__next_;
                __node_insert_multi(__cache->__upcast());
                __cache = __next;
            }
#ifndef _LIBCPP_NO_EXCEPTIONS
        }
        catch (...)
        {
            __deallocate_node(__cache);
            throw;
        }
#endif // _LIBCPP_NO_EXCEPTIONS
        __deallocate_node(__cache);
    }
    for (; __first != __last; ++__first)
        __insert_multi(_NodeTypes::__get_value(*__first));
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
inline
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::begin() _NOEXCEPT
{
    return iterator(__p1_.first().__next_, this);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
inline
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::end() _NOEXCEPT
{
    return iterator(nullptr, this);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
inline
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::const_iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::begin() const _NOEXCEPT
{
    return const_iterator(__p1_.first().__next_, this);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
inline
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::const_iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::end() const _NOEXCEPT
{
    return const_iterator(nullptr, this);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::clear() _NOEXCEPT
{
    if (size() > 0)
    {
        __deallocate_node(__p1_.first().__next_);
        __p1_.first().__next_ = nullptr;
        size_type __bc = bucket_count();
        for (size_type __i = 0; __i < __bc; ++__i)
            __bucket_list_[__i] = nullptr;
        size() = 0;
    }
}


// Prepare the container for an insertion of the value __value with the hash
// __hash. This does a lookup into the container to see if __value is already
// present, and performs a rehash if necessary. Returns a pointer to the
// existing element if it exists, otherwise nullptr.
//
// Note that this function does forward exceptions if key_eq() throws, and never
// mutates __value or actually inserts into the map.
template <class _Tp, class _Hash, class _Equal, class _Alloc>
_LIBCPP_INLINE_VISIBILITY
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::__next_pointer
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_insert_unique_prepare(
    size_t __hash, value_type& __value)
{
    size_type __bc = bucket_count();

    if (__bc != 0)
    {
        size_t __chash = std::__constrain_hash(__hash, __bc);
        __next_pointer __ndptr = __bucket_list_[__chash];
        if (__ndptr != nullptr)
        {
            for (__ndptr = __ndptr->__next_; __ndptr != nullptr &&
                                             std::__constrain_hash(__ndptr->__hash(), __bc) == __chash;
                                                     __ndptr = __ndptr->__next_)
            {
                if (key_eq()(__ndptr->__upcast()->__value_, __value))
                    return __ndptr;
            }
        }
    }
    if (size()+1 > __bc * max_load_factor() || __bc == 0)
    {
        __rehash_unique(_VSTD::max<size_type>(2 * __bc + !std::__is_hash_power2(__bc),
                                     size_type(std::ceil(float(size() + 1) / max_load_factor()))));
    }
    return nullptr;
}

// Insert the node __nd into the container by pushing it into the right bucket,
// and updating size(). Assumes that __nd->__hash is up-to-date, and that
// rehashing has already occurred and that no element with the same key exists
// in the map.
template <class _Tp, class _Hash, class _Equal, class _Alloc>
_LIBCPP_INLINE_VISIBILITY
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_insert_unique_perform(
    __node_pointer __nd) _NOEXCEPT
{
    size_type __bc = bucket_count();
    size_t __chash = std::__constrain_hash(__nd->__hash(), __bc);
    // insert_after __bucket_list_[__chash], or __first_node if bucket is null
    __next_pointer __pn = __bucket_list_[__chash];
    if (__pn == nullptr)
    {
        __pn =__p1_.first().__ptr();
        __nd->__next_ = __pn->__next_;
        __pn->__next_ = __nd->__ptr();
        // fix up __bucket_list_
        __bucket_list_[__chash] = __pn;
        if (__nd->__next_ != nullptr)
            __bucket_list_[std::__constrain_hash(__nd->__next_->__hash(), __bc)] = __nd->__ptr();
    }
    else
    {
        __nd->__next_ = __pn->__next_;
        __pn->__next_ = __nd->__ptr();
    }
    ++size();
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator, bool>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_insert_unique(__node_pointer __nd)
{
    __nd->__hash_ = hash_function()(__nd->__value_);
    __next_pointer __existing_node =
        __node_insert_unique_prepare(__nd->__hash(), __nd->__value_);

    // Insert the node, unless it already exists in the container.
    bool __inserted = false;
    if (__existing_node == nullptr)
    {
        __node_insert_unique_perform(__nd);
        __existing_node = __nd->__ptr();
        __inserted = true;
    }
    return pair<iterator, bool>(iterator(__existing_node, this), __inserted);
}

// Prepare the container for an insertion of the value __cp_val with the hash
// __cp_hash. This does a lookup into the container to see if __cp_value is
// already present, and performs a rehash if necessary. Returns a pointer to the
// last occurrence of __cp_val in the map.
//
// Note that this function does forward exceptions if key_eq() throws, and never
// mutates __value or actually inserts into the map.
template <class _Tp, class _Hash, class _Equal, class _Alloc>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::__next_pointer
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_insert_multi_prepare(
    size_t __cp_hash, value_type& __cp_val)
{
    size_type __bc = bucket_count();
    if (size()+1 > __bc * max_load_factor() || __bc == 0)
    {
        __rehash_multi(_VSTD::max<size_type>(2 * __bc + !std::__is_hash_power2(__bc),
                       size_type(std::ceil(float(size() + 1) / max_load_factor()))));
        __bc = bucket_count();
    }
    size_t __chash = std::__constrain_hash(__cp_hash, __bc);
    __next_pointer __pn = __bucket_list_[__chash];
    if (__pn != nullptr)
    {
        for (bool __found = false; __pn->__next_ != nullptr &&
                                   std::__constrain_hash(__pn->__next_->__hash(), __bc) == __chash;
                                                           __pn = __pn->__next_)
        {
            //      __found    key_eq()     action
            //      false       false       loop
            //      true        true        loop
            //      false       true        set __found to true
            //      true        false       break
            if (__found != (__pn->__next_->__hash() == __cp_hash &&
                            key_eq()(__pn->__next_->__upcast()->__value_, __cp_val)))
            {
                if (!__found)
                    __found = true;
                else
                    break;
            }
        }
    }
    return __pn;
}

// Insert the node __cp into the container after __pn (which is the last node in
// the bucket that compares equal to __cp). Rehashing, and checking for
// uniqueness has already been performed (in __node_insert_multi_prepare), so
// all we need to do is update the bucket and size(). Assumes that __cp->__hash
// is up-to-date.
template <class _Tp, class _Hash, class _Equal, class _Alloc>
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_insert_multi_perform(
    __node_pointer __cp, __next_pointer __pn) _NOEXCEPT
{
    size_type __bc = bucket_count();
    size_t __chash = std::__constrain_hash(__cp->__hash_, __bc);
    if (__pn == nullptr)
    {
        __pn =__p1_.first().__ptr();
        __cp->__next_ = __pn->__next_;
        __pn->__next_ = __cp->__ptr();
        // fix up __bucket_list_
        __bucket_list_[__chash] = __pn;
        if (__cp->__next_ != nullptr)
            __bucket_list_[std::__constrain_hash(__cp->__next_->__hash(), __bc)]
                = __cp->__ptr();
    }
    else
    {
        __cp->__next_ = __pn->__next_;
        __pn->__next_ = __cp->__ptr();
        if (__cp->__next_ != nullptr)
        {
            size_t __nhash = std::__constrain_hash(__cp->__next_->__hash(), __bc);
            if (__nhash != __chash)
                __bucket_list_[__nhash] = __cp->__ptr();
        }
    }
    ++size();
}


template <class _Tp, class _Hash, class _Equal, class _Alloc>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_insert_multi(__node_pointer __cp)
{
    __cp->__hash_ = hash_function()(__cp->__value_);
    __next_pointer __pn = __node_insert_multi_prepare(__cp->__hash(), __cp->__value_);
    __node_insert_multi_perform(__cp, __pn);

    return iterator(__cp->__ptr(), this);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_insert_multi(
        const_iterator __p, __node_pointer __cp)
{
    _LIBCPP_DEBUG_ASSERT(__get_const_db()->__find_c_from_i(_VSTD::addressof(__p)) == this,
                         "unordered container::emplace_hint(const_iterator, args...) called with an iterator not"
                         " referring to this unordered container");
    if (__p != end() && key_eq()(*__p, __cp->__value_))
    {
        __next_pointer __np = __p.__node_;
        __cp->__hash_ = __np->__hash();
        size_type __bc = bucket_count();
        if (size()+1 > __bc * max_load_factor() || __bc == 0)
        {
            __rehash_multi(_VSTD::max<size_type>(2 * __bc + !std::__is_hash_power2(__bc),
                           size_type(std::ceil(float(size() + 1) / max_load_factor()))));
            __bc = bucket_count();
        }
        size_t __chash = std::__constrain_hash(__cp->__hash_, __bc);
        __next_pointer __pp = __bucket_list_[__chash];
        while (__pp->__next_ != __np)
            __pp = __pp->__next_;
        __cp->__next_ = __np;
        __pp->__next_ = static_cast<__next_pointer>(__cp);
        ++size();
        return iterator(static_cast<__next_pointer>(__cp), this);
    }
    return __node_insert_multi(__cp);
}



template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Key, class ..._Args>
pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator, bool>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__emplace_unique_key_args(_Key const& __k, _Args&&... __args)
{

    size_t __hash = hash_function()(__k);
    size_type __bc = bucket_count();
    bool __inserted = false;
    __next_pointer __nd;
    size_t __chash;
    if (__bc != 0)
    {
        __chash = std::__constrain_hash(__hash, __bc);
        __nd = __bucket_list_[__chash];
        if (__nd != nullptr)
        {
            for (__nd = __nd->__next_; __nd != nullptr &&
                (__nd->__hash() == __hash || std::__constrain_hash(__nd->__hash(), __bc) == __chash);
                                                           __nd = __nd->__next_)
            {
                if (key_eq()(__nd->__upcast()->__value_, __k))
                    goto __done;
            }
        }
    }
    {
        __node_holder __h = __construct_node_hash(__hash, _VSTD::forward<_Args>(__args)...);
        if (size()+1 > __bc * max_load_factor() || __bc == 0)
        {
            __rehash_unique(_VSTD::max<size_type>(2 * __bc + !std::__is_hash_power2(__bc),
                           size_type(std::ceil(float(size() + 1) / max_load_factor()))));
            __bc = bucket_count();
            __chash = std::__constrain_hash(__hash, __bc);
        }
        // insert_after __bucket_list_[__chash], or __first_node if bucket is null
        __next_pointer __pn = __bucket_list_[__chash];
        if (__pn == nullptr)
        {
            __pn = __p1_.first().__ptr();
            __h->__next_ = __pn->__next_;
            __pn->__next_ = __h.get()->__ptr();
            // fix up __bucket_list_
            __bucket_list_[__chash] = __pn;
            if (__h->__next_ != nullptr)
                __bucket_list_[std::__constrain_hash(__h->__next_->__hash(), __bc)]
                    = __h.get()->__ptr();
        }
        else
        {
            __h->__next_ = __pn->__next_;
            __pn->__next_ = static_cast<__next_pointer>(__h.get());
        }
        __nd = static_cast<__next_pointer>(__h.release());
        // increment size
        ++size();
        __inserted = true;
    }
__done:
    return pair<iterator, bool>(iterator(__nd, this), __inserted);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class... _Args>
pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator, bool>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__emplace_unique_impl(_Args&&... __args)
{
    __node_holder __h = __construct_node(_VSTD::forward<_Args>(__args)...);
    pair<iterator, bool> __r = __node_insert_unique(__h.get());
    if (__r.second)
        __h.release();
    return __r;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class... _Args>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__emplace_multi(_Args&&... __args)
{
    __node_holder __h = __construct_node(_VSTD::forward<_Args>(__args)...);
    iterator __r = __node_insert_multi(__h.get());
    __h.release();
    return __r;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class... _Args>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__emplace_hint_multi(
        const_iterator __p, _Args&&... __args)
{
    _LIBCPP_DEBUG_ASSERT(__get_const_db()->__find_c_from_i(_VSTD::addressof(__p)) == this,
                         "unordered container::emplace_hint(const_iterator, args...) called with an iterator not"
                         " referring to this unordered container");
    __node_holder __h = __construct_node(_VSTD::forward<_Args>(__args)...);
    iterator __r = __node_insert_multi(__p, __h.get());
    __h.release();
    return __r;
}

#if _LIBCPP_STD_VER > 14
template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _NodeHandle, class _InsertReturnType>
_LIBCPP_INLINE_VISIBILITY
_InsertReturnType
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_handle_insert_unique(
    _NodeHandle&& __nh)
{
    if (__nh.empty())
        return _InsertReturnType{end(), false, _NodeHandle()};
    pair<iterator, bool> __result = __node_insert_unique(__nh.__ptr_);
    if (__result.second)
        __nh.__release_ptr();
    return _InsertReturnType{__result.first, __result.second, _VSTD::move(__nh)};
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _NodeHandle>
_LIBCPP_INLINE_VISIBILITY
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_handle_insert_unique(
    const_iterator, _NodeHandle&& __nh)
{
    if (__nh.empty())
        return end();
    pair<iterator, bool> __result = __node_insert_unique(__nh.__ptr_);
    if (__result.second)
        __nh.__release_ptr();
    return __result.first;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _NodeHandle>
_LIBCPP_INLINE_VISIBILITY
_NodeHandle
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_handle_extract(
    key_type const& __key)
{
    iterator __i = find(__key);
    if (__i == end())
        return _NodeHandle();
    return __node_handle_extract<_NodeHandle>(__i);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _NodeHandle>
_LIBCPP_INLINE_VISIBILITY
_NodeHandle
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_handle_extract(
    const_iterator __p)
{
    allocator_type __alloc(__node_alloc());
    return _NodeHandle(remove(__p).release(), __alloc);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Table>
_LIBCPP_INLINE_VISIBILITY
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_handle_merge_unique(
    _Table& __source)
{
    static_assert(is_same<__node, typename _Table::__node>::value, "");

    for (typename _Table::iterator __it = __source.begin();
         __it != __source.end();)
    {
        __node_pointer __src_ptr = __it.__node_->__upcast();
        size_t __hash = hash_function()(__src_ptr->__value_);
        __next_pointer __existing_node =
            __node_insert_unique_prepare(__hash, __src_ptr->__value_);
        auto __prev_iter = __it++;
        if (__existing_node == nullptr)
        {
            (void)__source.remove(__prev_iter).release();
            __src_ptr->__hash_ = __hash;
            __node_insert_unique_perform(__src_ptr);
        }
    }
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _NodeHandle>
_LIBCPP_INLINE_VISIBILITY
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_handle_insert_multi(
    _NodeHandle&& __nh)
{
    if (__nh.empty())
        return end();
    iterator __result = __node_insert_multi(__nh.__ptr_);
    __nh.__release_ptr();
    return __result;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _NodeHandle>
_LIBCPP_INLINE_VISIBILITY
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_handle_insert_multi(
    const_iterator __hint, _NodeHandle&& __nh)
{
    if (__nh.empty())
        return end();
    iterator __result = __node_insert_multi(__hint, __nh.__ptr_);
    __nh.__release_ptr();
    return __result;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Table>
_LIBCPP_INLINE_VISIBILITY
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_handle_merge_multi(
    _Table& __source)
{
    static_assert(is_same<typename _Table::__node, __node>::value, "");

    for (typename _Table::iterator __it = __source.begin();
         __it != __source.end();)
    {
        __node_pointer __src_ptr = __it.__node_->__upcast();
        size_t __src_hash = hash_function()(__src_ptr->__value_);
        __next_pointer __pn =
            __node_insert_multi_prepare(__src_hash, __src_ptr->__value_);
        (void)__source.remove(__it++).release();
        __src_ptr->__hash_ = __src_hash;
        __node_insert_multi_perform(__src_ptr, __pn);
    }
}
#endif // _LIBCPP_STD_VER > 14

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <bool _UniqueKeys>
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__rehash(size_type __n)
_LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK
{
    if (__n == 1)
        __n = 2;
    else if (__n & (__n - 1))
        __n = std::__next_prime(__n);
    size_type __bc = bucket_count();
    if (__n > __bc)
        __do_rehash<_UniqueKeys>(__n);
    else if (__n < __bc)
    {
        __n = _VSTD::max<size_type>
              (
                  __n,
                  std::__is_hash_power2(__bc) ? std::__next_hash_pow2(size_t(std::ceil(float(size()) / max_load_factor()))) :
                                           std::__next_prime(size_t(std::ceil(float(size()) / max_load_factor())))
              );
        if (__n < __bc)
            __do_rehash<_UniqueKeys>(__n);
    }
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <bool _UniqueKeys>
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__do_rehash(size_type __nbc)
{
    std::__debug_db_invalidate_all(this);
    __pointer_allocator& __npa = __bucket_list_.get_deleter().__alloc();
    __bucket_list_.reset(__nbc > 0 ?
                      __pointer_alloc_traits::allocate(__npa, __nbc) : nullptr);
    __bucket_list_.get_deleter().size() = __nbc;
    if (__nbc > 0)
    {
        for (size_type __i = 0; __i < __nbc; ++__i)
            __bucket_list_[__i] = nullptr;
        __next_pointer __pp = __p1_.first().__ptr();
        __next_pointer __cp = __pp->__next_;
        if (__cp != nullptr)
        {
            size_type __chash = std::__constrain_hash(__cp->__hash(), __nbc);
            __bucket_list_[__chash] = __pp;
            size_type __phash = __chash;
            for (__pp = __cp, void(), __cp = __cp->__next_; __cp != nullptr;
                                                           __cp = __pp->__next_)
            {
                __chash = std::__constrain_hash(__cp->__hash(), __nbc);
                if (__chash == __phash)
                    __pp = __cp;
                else
                {
                    if (__bucket_list_[__chash] == nullptr)
                    {
                        __bucket_list_[__chash] = __pp;
                        __pp = __cp;
                        __phash = __chash;
                    }
                    else
                    {
                        __next_pointer __np = __cp;
                        if _LIBCPP_CONSTEXPR_SINCE_CXX17 (!_UniqueKeys)
                        {
                            for (; __np->__next_ != nullptr &&
                                   key_eq()(__cp->__upcast()->__value_,
                                            __np->__next_->__upcast()->__value_);
                                                               __np = __np->__next_)
                                ;
                        }
                        __pp->__next_ = __np->__next_;
                        __np->__next_ = __bucket_list_[__chash]->__next_;
                        __bucket_list_[__chash]->__next_ = __cp;

                    }
                }
            }
        }
    }
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Key>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::find(const _Key& __k)
{
    size_t __hash = hash_function()(__k);
    size_type __bc = bucket_count();
    if (__bc != 0)
    {
        size_t __chash = std::__constrain_hash(__hash, __bc);
        __next_pointer __nd = __bucket_list_[__chash];
        if (__nd != nullptr)
        {
            for (__nd = __nd->__next_; __nd != nullptr &&
                (__nd->__hash() == __hash
                  || std::__constrain_hash(__nd->__hash(), __bc) == __chash);
                                                           __nd = __nd->__next_)
            {
                if ((__nd->__hash() == __hash)
                    && key_eq()(__nd->__upcast()->__value_, __k))
                    return iterator(__nd, this);
            }
        }
    }
    return end();
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Key>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::const_iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::find(const _Key& __k) const
{
    size_t __hash = hash_function()(__k);
    size_type __bc = bucket_count();
    if (__bc != 0)
    {
        size_t __chash = std::__constrain_hash(__hash, __bc);
        __next_pointer __nd = __bucket_list_[__chash];
        if (__nd != nullptr)
        {
            for (__nd = __nd->__next_; __nd != nullptr &&
                (__hash == __nd->__hash()
                    || std::__constrain_hash(__nd->__hash(), __bc) == __chash);
                                                           __nd = __nd->__next_)
            {
                if ((__nd->__hash() == __hash)
                    && key_eq()(__nd->__upcast()->__value_, __k))
                    return const_iterator(__nd, this);
            }
        }

    }
    return end();
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class ..._Args>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_holder
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__construct_node(_Args&& ...__args)
{
    static_assert(!__is_hash_value_type<_Args...>::value,
                  "Construct cannot be called with a hash value type");
    __node_allocator& __na = __node_alloc();
    __node_holder __h(__node_traits::allocate(__na, 1), _Dp(__na));
    __node_traits::construct(__na, _NodeTypes::__get_ptr(__h->__value_), _VSTD::forward<_Args>(__args)...);
    __h.get_deleter().__value_constructed = true;
    __h->__hash_ = hash_function()(__h->__value_);
    __h->__next_ = nullptr;
    return __h;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _First, class ..._Rest>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_holder
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__construct_node_hash(
    size_t __hash, _First&& __f, _Rest&& ...__rest)
{
    static_assert(!__is_hash_value_type<_First, _Rest...>::value,
                  "Construct cannot be called with a hash value type");
    __node_allocator& __na = __node_alloc();
    __node_holder __h(__node_traits::allocate(__na, 1), _Dp(__na));
    __node_traits::construct(__na, _NodeTypes::__get_ptr(__h->__value_),
                             _VSTD::forward<_First>(__f),
                             _VSTD::forward<_Rest>(__rest)...);
    __h.get_deleter().__value_constructed = true;
    __h->__hash_ = __hash;
    __h->__next_ = nullptr;
    return __h;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::erase(const_iterator __p)
{
    __next_pointer __np = __p.__node_;
    _LIBCPP_DEBUG_ASSERT(__get_const_db()->__find_c_from_i(_VSTD::addressof(__p)) == this,
                         "unordered container erase(iterator) called with an iterator not"
                         " referring to this container");
    _LIBCPP_ASSERT(__p != end(),
                   "unordered container erase(iterator) called with a non-dereferenceable iterator");
    iterator __r(__np, this);
    ++__r;
    remove(__p);
    return __r;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
__hash_table<_Tp, _Hash, _Equal, _Alloc>::erase(const_iterator __first,
                                                const_iterator __last)
{
    _LIBCPP_DEBUG_ASSERT(__get_const_db()->__find_c_from_i(_VSTD::addressof(__first)) == this,
                         "unordered container::erase(iterator, iterator) called with an iterator not"
                         " referring to this container");
    _LIBCPP_DEBUG_ASSERT(__get_const_db()->__find_c_from_i(_VSTD::addressof(__last)) == this,
                         "unordered container::erase(iterator, iterator) called with an iterator not"
                         " referring to this container");
    for (const_iterator __p = __first; __first != __last; __p = __first)
    {
        ++__first;
        erase(__p);
    }
    __next_pointer __np = __last.__node_;
    return iterator (__np, this);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Key>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::size_type
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__erase_unique(const _Key& __k)
{
    iterator __i = find(__k);
    if (__i == end())
        return 0;
    erase(__i);
    return 1;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Key>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::size_type
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__erase_multi(const _Key& __k)
{
    size_type __r = 0;
    iterator __i = find(__k);
    if (__i != end())
    {
        iterator __e = end();
        do
        {
            erase(__i++);
            ++__r;
        } while (__i != __e && key_eq()(*__i, __k));
    }
    return __r;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_holder
__hash_table<_Tp, _Hash, _Equal, _Alloc>::remove(const_iterator __p) _NOEXCEPT
{
    // current node
    __next_pointer __cn = __p.__node_;
    size_type __bc = bucket_count();
    size_t __chash = std::__constrain_hash(__cn->__hash(), __bc);
    // find previous node
    __next_pointer __pn = __bucket_list_[__chash];
    for (; __pn->__next_ != __cn; __pn = __pn->__next_)
        ;
    // Fix up __bucket_list_
        // if __pn is not in same bucket (before begin is not in same bucket) &&
        //    if __cn->__next_ is not in same bucket (nullptr is not in same bucket)
    if (__pn == __p1_.first().__ptr()
            || std::__constrain_hash(__pn->__hash(), __bc) != __chash)
    {
        if (__cn->__next_ == nullptr
            || std::__constrain_hash(__cn->__next_->__hash(), __bc) != __chash)
            __bucket_list_[__chash] = nullptr;
    }
        // if __cn->__next_ is not in same bucket (nullptr is in same bucket)
    if (__cn->__next_ != nullptr)
    {
        size_t __nhash = std::__constrain_hash(__cn->__next_->__hash(), __bc);
        if (__nhash != __chash)
            __bucket_list_[__nhash] = __pn;
    }
    // remove __cn
    __pn->__next_ = __cn->__next_;
    __cn->__next_ = nullptr;
    --size();
#ifdef _LIBCPP_ENABLE_DEBUG_MODE
    __c_node* __c = __get_db()->__find_c_and_lock(this);
    for (__i_node** __dp = __c->end_; __dp != __c->beg_; )
    {
        --__dp;
        iterator* __i = static_cast<iterator*>((*__dp)->__i_);
        if (__i->__node_ == __cn)
        {
            (*__dp)->__c_ = nullptr;
            if (--__c->end_ != __dp)
                _VSTD::memmove(__dp, __dp+1, (__c->end_ - __dp)*sizeof(__i_node*));
        }
    }
    __get_db()->unlock();
#endif
    return __node_holder(__cn->__upcast(), _Dp(__node_alloc(), true));
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Key>
inline
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::size_type
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__count_unique(const _Key& __k) const
{
    return static_cast<size_type>(find(__k) != end());
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Key>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::size_type
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__count_multi(const _Key& __k) const
{
    size_type __r = 0;
    const_iterator __i = find(__k);
    if (__i != end())
    {
        const_iterator __e = end();
        do
        {
            ++__i;
            ++__r;
        } while (__i != __e && key_eq()(*__i, __k));
    }
    return __r;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Key>
pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator,
     typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__equal_range_unique(
        const _Key& __k)
{
    iterator __i = find(__k);
    iterator __j = __i;
    if (__i != end())
        ++__j;
    return pair<iterator, iterator>(__i, __j);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Key>
pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::const_iterator,
     typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::const_iterator>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__equal_range_unique(
        const _Key& __k) const
{
    const_iterator __i = find(__k);
    const_iterator __j = __i;
    if (__i != end())
        ++__j;
    return pair<const_iterator, const_iterator>(__i, __j);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Key>
pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator,
     typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__equal_range_multi(
        const _Key& __k)
{
    iterator __i = find(__k);
    iterator __j = __i;
    if (__i != end())
    {
        iterator __e = end();
        do
        {
            ++__j;
        } while (__j != __e && key_eq()(*__j, __k));
    }
    return pair<iterator, iterator>(__i, __j);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _Key>
pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::const_iterator,
     typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::const_iterator>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__equal_range_multi(
        const _Key& __k) const
{
    const_iterator __i = find(__k);
    const_iterator __j = __i;
    if (__i != end())
    {
        const_iterator __e = end();
        do
        {
            ++__j;
        } while (__j != __e && key_eq()(*__j, __k));
    }
    return pair<const_iterator, const_iterator>(__i, __j);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
void
__hash_table<_Tp, _Hash, _Equal, _Alloc>::swap(__hash_table& __u)
#if _LIBCPP_STD_VER <= 11
    _NOEXCEPT_(
        __is_nothrow_swappable<hasher>::value && __is_nothrow_swappable<key_equal>::value
        && (!allocator_traits<__pointer_allocator>::propagate_on_container_swap::value
              || __is_nothrow_swappable<__pointer_allocator>::value)
        && (!__node_traits::propagate_on_container_swap::value
              || __is_nothrow_swappable<__node_allocator>::value)
            )
#else
  _NOEXCEPT_(__is_nothrow_swappable<hasher>::value && __is_nothrow_swappable<key_equal>::value)
#endif
{
    _LIBCPP_ASSERT(__node_traits::propagate_on_container_swap::value ||
                   this->__node_alloc() == __u.__node_alloc(),
                   "list::swap: Either propagate_on_container_swap must be true"
                   " or the allocators must compare equal");
    {
    __node_pointer_pointer __npp = __bucket_list_.release();
    __bucket_list_.reset(__u.__bucket_list_.release());
    __u.__bucket_list_.reset(__npp);
    }
    _VSTD::swap(__bucket_list_.get_deleter().size(), __u.__bucket_list_.get_deleter().size());
    _VSTD::__swap_allocator(__bucket_list_.get_deleter().__alloc(),
             __u.__bucket_list_.get_deleter().__alloc());
    _VSTD::__swap_allocator(__node_alloc(), __u.__node_alloc());
    _VSTD::swap(__p1_.first().__next_, __u.__p1_.first().__next_);
    __p2_.swap(__u.__p2_);
    __p3_.swap(__u.__p3_);
    if (size() > 0)
        __bucket_list_[std::__constrain_hash(__p1_.first().__next_->__hash(), bucket_count())] =
            __p1_.first().__ptr();
    if (__u.size() > 0)
        __u.__bucket_list_[std::__constrain_hash(__u.__p1_.first().__next_->__hash(), __u.bucket_count())] =
            __u.__p1_.first().__ptr();
    std::__debug_db_swap(this, std::addressof(__u));
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::size_type
__hash_table<_Tp, _Hash, _Equal, _Alloc>::bucket_size(size_type __n) const
{
    _LIBCPP_ASSERT(__n < bucket_count(),
        "unordered container::bucket_size(n) called with n >= bucket_count()");
    __next_pointer __np = __bucket_list_[__n];
    size_type __bc = bucket_count();
    size_type __r = 0;
    if (__np != nullptr)
    {
        for (__np = __np->__next_; __np != nullptr &&
                                   std::__constrain_hash(__np->__hash(), __bc) == __n;
                                                         __np = __np->__next_, (void) ++__r)
            ;
    }
    return __r;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
inline _LIBCPP_INLINE_VISIBILITY
void
swap(__hash_table<_Tp, _Hash, _Equal, _Alloc>& __x,
     __hash_table<_Tp, _Hash, _Equal, _Alloc>& __y)
    _NOEXCEPT_(_NOEXCEPT_(__x.swap(__y)))
{
    __x.swap(__y);
}

#ifdef _LIBCPP_ENABLE_DEBUG_MODE

template <class _Tp, class _Hash, class _Equal, class _Alloc>
bool
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__dereferenceable(const const_iterator* __i) const
{
    return __i->__node_ != nullptr;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
bool
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__decrementable(const const_iterator*) const
{
    return false;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
bool
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__addable(const const_iterator*, ptrdiff_t) const
{
    return false;
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
bool
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__subscriptable(const const_iterator*, ptrdiff_t) const
{
    return false;
}

#endif // _LIBCPP_ENABLE_DEBUG_MODE

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___HASH_TABLE
