libcxx/include/__hash_table

// -*- 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/fill_n.h>
#include <__algorithm/max.h>
#include <__algorithm/min.h>
#include <__assert>
#include <__bit/countl.h>
#include <__config>
#include <__cstddef/ptrdiff_t.h>
#include <__cstddef/size_t.h>
#include <__functional/hash.h>
#include <__iterator/iterator_traits.h>
#include <__math/rounding_functions.h>
#include <__memory/addressof.h>
#include <__memory/allocator_traits.h>
#include <__memory/compressed_pair.h>
#include <__memory/construct_at.h>
#include <__memory/pointer_traits.h>
#include <__memory/swap_allocator.h>
#include <__memory/unique_ptr.h>
#include <__new/launder.h>
#include <__type_traits/copy_cvref.h>
#include <__type_traits/enable_if.h>
#include <__type_traits/invoke.h>
#include <__type_traits/is_const.h>
#include <__type_traits/is_constructible.h>
#include <__type_traits/is_nothrow_assignable.h>
#include <__type_traits/is_nothrow_constructible.h>
#include <__type_traits/is_reference.h>
#include <__type_traits/is_same.h>
#include <__type_traits/is_swappable.h>
#include <__type_traits/remove_const.h>
#include <__type_traits/remove_cvref.h>
#include <__utility/exception_guard.h>
#include <__utility/exchange.h>
#include <__utility/forward.h>
#include <__utility/move.h>
#include <__utility/pair.h>
#include <__utility/scope_guard.h>
#include <__utility/swap.h>
#include <__utility/try_key_extraction.h>
#include <limits>

#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_BEGIN_EXPLICIT_ABI_ANNOTATIONS
_LIBCPP_EXPORTED_FROM_ABI size_t __next_prime(size_t __n);
_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS

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;
  typedef __node_base_pointer __next_pointer;

  __next_pointer __next_;

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

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

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

  _LIBCPP_HIDE_FROM_ABI __hash_node_base() _NOEXCEPT : __next_(nullptr) {}
  _LIBCPP_HIDE_FROM_ABI explicit __hash_node_base(__next_pointer __next) _NOEXCEPT : __next_(__next) {}
};

template <class _Tp>
struct __get_hash_node_value_type {
  using type _LIBCPP_NODEBUG = _Tp;
};

template <class _Key, class _Tp>
struct __get_hash_node_value_type<__hash_value_type<_Key, _Tp> > {
  using type _LIBCPP_NODEBUG = pair<const _Key, _Tp>;
};

template <class _Tp>
using __get_hash_node_value_type_t _LIBCPP_NODEBUG = typename __get_hash_node_value_type<_Tp>::type;

template <class _Tp>
struct __get_hash_node_key_type {
  using type _LIBCPP_NODEBUG = _Tp;
};

template <class _Key, class _Tp>
struct __get_hash_node_key_type<__hash_value_type<_Key, _Tp> > {
  using type _LIBCPP_NODEBUG = _Key;
};

template <class _Tp>
using __get_hash_node_key_type_t _LIBCPP_NODEBUG = typename __get_hash_node_key_type<_Tp>::type;

template <class _Tp, class _VoidPtr>
struct __hash_node : public __hash_node_base< __rebind_pointer_t<_VoidPtr, __hash_node<_Tp, _VoidPtr> > > {
  using __node_value_type _LIBCPP_NODEBUG = __get_hash_node_value_type_t<_Tp>;
  using _Base _LIBCPP_NODEBUG          = __hash_node_base<__rebind_pointer_t<_VoidPtr, __hash_node<_Tp, _VoidPtr> > >;
  using __next_pointer _LIBCPP_NODEBUG = typename _Base::__next_pointer;

  size_t __hash_;

  // We allow starting the lifetime of nodes without initializing the value held by the node,
  // since that is handled by the hash table itself in order to be allocator-aware.
#ifndef _LIBCPP_CXX03_LANG

private:
  union {
    __node_value_type __value_;
  };

public:
  _LIBCPP_HIDE_FROM_ABI __node_value_type& __get_value() { return __value_; }
#else

private:
  _ALIGNAS_TYPE(__node_value_type) char __buffer_[sizeof(__node_value_type)];

public:
  _LIBCPP_HIDE_FROM_ABI __node_value_type& __get_value() {
    return *std::__launder(reinterpret_cast<__node_value_type*>(&__buffer_));
  }
#endif

  template <class _Alloc, class... _Args>
  _LIBCPP_HIDE_FROM_ABI explicit __hash_node(size_t __hash, _Alloc& __na, _Args&&... __args)
      : _Base(nullptr), __hash_(__hash) {
    allocator_traits<_Alloc>::construct(__na, std::addressof(__get_value()), std::forward<_Args>(__args)...);
  }

  _LIBCPP_HIDE_FROM_ABI ~__hash_node() {}
};

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

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

inline _LIBCPP_HIDE_FROM_ABI size_t __next_hash_pow2(size_t __n) {
  return __n < 2 ? __n : (size_t(1) << (numeric_limits<size_t>::digits - std::__countl_zero(__n - 1)));
}

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

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

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

  typedef typename __hash_node_base<_NodePtr>::__next_pointer __next_pointer;

  using __node_value_type _LIBCPP_NODEBUG = __get_hash_node_value_type_t<_Tp>;

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 _NodePtr>
class __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;
  using difference_type = ptrdiff_t;
  typedef value_type& reference;
  using pointer = __rebind_pointer_t<_NodePtr, value_type>;

  _LIBCPP_HIDE_FROM_ABI __hash_iterator() _NOEXCEPT : __node_(nullptr) {}

  _LIBCPP_HIDE_FROM_ABI reference operator*() const {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "Attempted to dereference a non-dereferenceable unordered container iterator");
    return __node_->__upcast()->__get_value();
  }

  _LIBCPP_HIDE_FROM_ABI pointer operator->() const {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "Attempted to dereference a non-dereferenceable unordered container iterator");
    return pointer_traits<pointer>::pointer_to(__node_->__upcast()->__get_value());
  }

  _LIBCPP_HIDE_FROM_ABI __hash_iterator& operator++() {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "Attempted to increment a non-incrementable unordered container iterator");
    __node_ = __node_->__next_;
    return *this;
  }

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

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

private:
  _LIBCPP_HIDE_FROM_ABI explicit __hash_iterator(__next_pointer __node) _NOEXCEPT : __node_(__node) {}

  template <class, class, class, class>
  friend class __hash_table;
  template <class>
  friend class __hash_const_iterator;
  template <class>
  friend class __hash_map_iterator;
  template <class, class, class, class, class>
  friend class unordered_map;
  template <class, class, class, class, class>
  friend class unordered_multimap;
};

template <class _NodePtr>
class __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;
  using difference_type = ptrdiff_t;
  typedef const value_type& reference;
  using pointer = __rebind_pointer_t<_NodePtr, const value_type>;

  _LIBCPP_HIDE_FROM_ABI __hash_const_iterator() _NOEXCEPT : __node_(nullptr) {}

  _LIBCPP_HIDE_FROM_ABI __hash_const_iterator(const __non_const_iterator& __x) _NOEXCEPT : __node_(__x.__node_) {}

  _LIBCPP_HIDE_FROM_ABI reference operator*() const {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "Attempted to dereference a non-dereferenceable unordered container const_iterator");
    return __node_->__upcast()->__get_value();
  }
  _LIBCPP_HIDE_FROM_ABI pointer operator->() const {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "Attempted to dereference a non-dereferenceable unordered container const_iterator");
    return pointer_traits<pointer>::pointer_to(__node_->__upcast()->__get_value());
  }

  _LIBCPP_HIDE_FROM_ABI __hash_const_iterator& operator++() {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "Attempted to increment a non-incrementable unordered container const_iterator");
    __node_ = __node_->__next_;
    return *this;
  }

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

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

private:
  _LIBCPP_HIDE_FROM_ABI explicit __hash_const_iterator(__next_pointer __node) _NOEXCEPT : __node_(__node) {}

  template <class, class, class, class>
  friend class __hash_table;
  template <class>
  friend class __hash_map_const_iterator;
  template <class, class, class, class, class>
  friend class unordered_map;
  template <class, class, class, class, class>
  friend class unordered_multimap;
};

template <class _NodePtr>
class __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;
  using difference_type = ptrdiff_t;
  typedef value_type& reference;
  using pointer = __rebind_pointer_t<_NodePtr, value_type>;

  _LIBCPP_HIDE_FROM_ABI __hash_local_iterator() _NOEXCEPT : __node_(nullptr) {}

  _LIBCPP_HIDE_FROM_ABI reference operator*() const {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "Attempted to dereference a non-dereferenceable unordered container local_iterator");
    return __node_->__upcast()->__get_value();
  }

  _LIBCPP_HIDE_FROM_ABI pointer operator->() const {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "Attempted to dereference a non-dereferenceable unordered container local_iterator");
    return pointer_traits<pointer>::pointer_to(__node_->__upcast()->__get_value());
  }

  _LIBCPP_HIDE_FROM_ABI __hash_local_iterator& operator++() {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "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_HIDE_FROM_ABI __hash_local_iterator operator++(int) {
    __hash_local_iterator __t(*this);
    ++(*this);
    return __t;
  }

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

private:
  _LIBCPP_HIDE_FROM_ABI explicit __hash_local_iterator(
      __next_pointer __node, size_t __bucket, size_t __bucket_count) _NOEXCEPT
      : __node_(__node),
        __bucket_(__bucket),
        __bucket_count_(__bucket_count) {
    if (__node_ != nullptr)
      __node_ = __node_->__next_;
  }

  template <class, class, class, class>
  friend class __hash_table;
  template <class>
  friend class __hash_const_local_iterator;
  template <class>
  friend class __hash_map_iterator;
};

template <class _ConstNodePtr>
class __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;
  using difference_type = ptrdiff_t;
  typedef const value_type& reference;
  using pointer = __rebind_pointer_t<_ConstNodePtr, const value_type>;

  _LIBCPP_HIDE_FROM_ABI __hash_const_local_iterator() _NOEXCEPT : __node_(nullptr) {}

  _LIBCPP_HIDE_FROM_ABI __hash_const_local_iterator(const __non_const_iterator& __x) _NOEXCEPT
      : __node_(__x.__node_),
        __bucket_(__x.__bucket_),
        __bucket_count_(__x.__bucket_count_) {}

  _LIBCPP_HIDE_FROM_ABI reference operator*() const {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "Attempted to dereference a non-dereferenceable unordered container const_local_iterator");
    return __node_->__upcast()->__get_value();
  }

  _LIBCPP_HIDE_FROM_ABI pointer operator->() const {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "Attempted to dereference a non-dereferenceable unordered container const_local_iterator");
    return pointer_traits<pointer>::pointer_to(__node_->__upcast()->__get_value());
  }

  _LIBCPP_HIDE_FROM_ABI __hash_const_local_iterator& operator++() {
    _LIBCPP_ASSERT_NON_NULL(
        __node_ != nullptr, "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_HIDE_FROM_ABI __hash_const_local_iterator operator++(int) {
    __hash_const_local_iterator __t(*this);
    ++(*this);
    return __t;
  }

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

private:
  _LIBCPP_HIDE_FROM_ABI explicit __hash_const_local_iterator(
      __next_pointer __node_ptr, size_t __bucket, size_t __bucket_count) _NOEXCEPT
      : __node_(__node_ptr),
        __bucket_(__bucket),
        __bucket_count_(__bucket_count) {
    if (__node_ != nullptr)
      __node_ = __node_->__next_;
  }

  template <class, class, class, class>
  friend class __hash_table;
  template <class>
  friend class __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;

  _LIBCPP_COMPRESSED_PAIR(size_type, __size_, allocator_type, __alloc_);

public:
  typedef typename __alloc_traits::pointer pointer;

  _LIBCPP_HIDE_FROM_ABI __bucket_list_deallocator() _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value)
      : __size_(0) {}

  _LIBCPP_HIDE_FROM_ABI __bucket_list_deallocator(const allocator_type& __a, size_type __size)
      _NOEXCEPT_(is_nothrow_copy_constructible<allocator_type>::value)
      : __size_(__size), __alloc_(__a) {}

  _LIBCPP_HIDE_FROM_ABI __bucket_list_deallocator(__bucket_list_deallocator&& __x)
      _NOEXCEPT_(is_nothrow_move_constructible<allocator_type>::value)
      : __size_(std::__exchange(__x.__size_, 0)), __alloc_(std::move(__x.__alloc_)) {}

  _LIBCPP_HIDE_FROM_ABI size_type& size() _NOEXCEPT { return __size_; }
  _LIBCPP_HIDE_FROM_ABI size_type size() const _NOEXCEPT { return __size_; }

  _LIBCPP_HIDE_FROM_ABI allocator_type& __alloc() _NOEXCEPT { return __alloc_; }
  _LIBCPP_HIDE_FROM_ABI const allocator_type& __alloc() const _NOEXCEPT { return __alloc_; }

  _LIBCPP_HIDE_FROM_ABI 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:
  allocator_type& __na_;

public:
  bool __value_constructed;

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

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

  _LIBCPP_HIDE_FROM_ABI void operator()(pointer __p) _NOEXCEPT {
    if (__value_constructed) {
      __alloc_traits::destroy(__na_, std::addressof(__p->__get_value()));
      std::__destroy_at(std::addressof(*__p));
    }
    if (__p)
      __alloc_traits::deallocate(__na_, __p, 1);
  }

  template <class>
  friend class __hash_map_node_destructor;
};

#if _LIBCPP_STD_VER >= 17
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(!__is_invocable_v<_Equal const&, _Key const&, _Key const&>,
                         "the specified comparator type does not provide a viable const call operator")
_LIBCPP_DIAGNOSE_WARNING(!__is_invocable_v<_Hash const&, _Key const&>,
                         "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:
  using value_type = __get_hash_node_value_type_t<_Tp>;
  using key_type   = __get_hash_node_key_type_t<_Tp>;

  typedef _Hash hasher;
  typedef _Equal key_equal;
  typedef _Alloc allocator_type;

private:
  typedef allocator_traits<allocator_type> __alloc_traits;

public:
  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
  using size_type = size_t;
#endif
  using difference_type = ptrdiff_t;

public:
  // Create __node

  using __void_pointer _LIBCPP_NODEBUG = typename __alloc_traits::void_pointer;

  using __node _LIBCPP_NODEBUG           = __hash_node<_Tp, __void_pointer>;
  using __node_allocator _LIBCPP_NODEBUG = __rebind_alloc<__alloc_traits, __node>;
  using __node_traits _LIBCPP_NODEBUG    = allocator_traits<__node_allocator>;
  using __node_pointer _LIBCPP_NODEBUG   = __rebind_pointer_t<__void_pointer, __node>;

  using __first_node _LIBCPP_NODEBUG        = __hash_node_base<__node_pointer>;
  using __node_base_pointer _LIBCPP_NODEBUG = __rebind_pointer_t<__void_pointer, __first_node>;
  using __next_pointer _LIBCPP_NODEBUG      = __node_base_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_;
  _LIBCPP_COMPRESSED_PAIR(__first_node, __first_node_, __node_allocator, __node_alloc_);
  _LIBCPP_COMPRESSED_PAIR(size_type, __size_, hasher, __hasher_);
  _LIBCPP_COMPRESSED_PAIR(float, __max_load_factor_, key_equal, __key_eq_);
  // --- Member data end ---

  _LIBCPP_HIDE_FROM_ABI size_type& size() _NOEXCEPT { return __size_; }

  _LIBCPP_HIDE_FROM_ABI void
  __copy_construct(__next_pointer __other_iter, __next_pointer __own_iter, size_t __current_chash) {
    auto __bucket_count = bucket_count();

    for (; __other_iter; __other_iter = __other_iter->__next_) {
      __node_holder __new_node = __construct_node_hash(__other_iter->__hash(), __other_iter->__upcast()->__get_value());

      size_t __new_chash = std::__constrain_hash(__new_node->__hash(), __bucket_count);
      if (__new_chash != __current_chash) {
        __bucket_list_[__new_chash] = __own_iter;
        __current_chash             = __new_chash;
      }

      __own_iter->__next_ = static_cast<__next_pointer>(__new_node.release());
      __own_iter          = __own_iter->__next_;
    }
  }

  _LIBCPP_HIDE_FROM_ABI void __copy_construct(__next_pointer __other_iter) {
    __next_pointer __own_iter = __first_node_.__ptr();
    // If copying a node throws, the nodes that have already been constructed and linked into the
    // list have to be deallocated. When this is called from the copy constructor the enclosing
    // __hash_table is not fully constructed yet, so its destructor would not run to release them.
    // This is also reached from operator= when assigning into an empty table; there the table
    // stays alive, so we must leave it in a valid empty state: besides releasing the nodes we
    // clear the bucket pointers, which were made to point into the now-deallocated node list.
    auto __guard = std::__make_exception_guard([&] {
      __deallocate_node_list(__first_node_.__next_);
      __first_node_.__next_ = nullptr;
      std::fill_n(__bucket_list_.get(), bucket_count(), nullptr);
    });
    {
      __node_holder __new_node = __construct_node_hash(__other_iter->__hash(), __other_iter->__upcast()->__get_value());
      __own_iter->__next_      = static_cast<__next_pointer>(__new_node.release());
    }

    size_t __current_chash          = std::__constrain_hash(__own_iter->__next_->__hash(), bucket_count());
    __bucket_list_[__current_chash] = __own_iter;
    __other_iter                    = __other_iter->__next_;
    __own_iter                      = __own_iter->__next_;
    __copy_construct(__other_iter, __own_iter, __current_chash);
    __guard.__complete();
  }

public:
  _LIBCPP_HIDE_FROM_ABI size_type size() const _NOEXCEPT { return __size_; }

  _LIBCPP_HIDE_FROM_ABI hasher& hash_function() _NOEXCEPT { return __hasher_; }
  _LIBCPP_HIDE_FROM_ABI const hasher& hash_function() const _NOEXCEPT { return __hasher_; }

  _LIBCPP_HIDE_FROM_ABI float& max_load_factor() _NOEXCEPT { return __max_load_factor_; }
  _LIBCPP_HIDE_FROM_ABI float max_load_factor() const _NOEXCEPT { return __max_load_factor_; }

  _LIBCPP_HIDE_FROM_ABI key_equal& key_eq() _NOEXCEPT { return __key_eq_; }
  _LIBCPP_HIDE_FROM_ABI const key_equal& key_eq() const _NOEXCEPT { return __key_eq_; }

  _LIBCPP_HIDE_FROM_ABI __node_allocator& __node_alloc() _NOEXCEPT { return __node_alloc_; }
  _LIBCPP_HIDE_FROM_ABI const __node_allocator& __node_alloc() const _NOEXCEPT { return __node_alloc_; }

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_HIDE_FROM_ABI __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_HIDE_FROM_ABI __hash_table(const hasher& __hf, const key_equal& __eql);
  _LIBCPP_HIDE_FROM_ABI __hash_table(const hasher& __hf, const key_equal& __eql, const allocator_type& __a);
  _LIBCPP_HIDE_FROM_ABI explicit __hash_table(const allocator_type& __a);
  _LIBCPP_HIDE_FROM_ABI __hash_table(const __hash_table& __u);
  _LIBCPP_HIDE_FROM_ABI __hash_table(const __hash_table& __u, const allocator_type& __a);
  _LIBCPP_HIDE_FROM_ABI __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);
  _LIBCPP_HIDE_FROM_ABI __hash_table(__hash_table&& __u, const allocator_type& __a);
  _LIBCPP_HIDE_FROM_ABI ~__hash_table();

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

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

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

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

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

  template <class... _Args>
  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __emplace_unique(_Args&&... __args) {
    return std::__try_key_extraction<key_type>(
        [this](const key_type& __key, _Args&&... __args2) {
          size_t __hash   = hash_function()(__key);
          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 ((__nd->__hash() == __hash) && key_eq()(__nd->__upcast()->__get_value(), __key))
                  goto __done;
              }
            }
          }
          {
            __node_holder __h = __construct_node_hash(__hash, std::forward<_Args>(__args2)...);
            if (size() + 1 > __bc * max_load_factor()) {
              __rehash_unique(std::max<size_type>(2 * __bc + !std::__is_hash_power2(__bc),
                                                  size_type(__math::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          = __first_node_.__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), __inserted);
        },
        [this](_Args&&... __args2) {
          __node_holder __h        = __construct_node(std::forward<_Args>(__args2)...);
          pair<iterator, bool> __r = __node_insert_unique(__h.get());
          if (__r.second)
            __h.release();
          return __r;
        },
        std::forward<_Args>(__args)...);
  }

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

  template <class _ValueT = _Tp, __enable_if_t<__is_hash_value_type<_ValueT>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void __insert_unique_from_orphaned_node(value_type&& __value) {
    __node_holder __h = __construct_node(const_cast<key_type&&>(__value.first), std::move(__value.second));
    __node_insert_unique(__h.get());
    __h.release();
  }

  template <class _ValueT = _Tp, __enable_if_t<!__is_hash_value_type<_ValueT>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void __insert_unique_from_orphaned_node(value_type&& __value) {
    __node_holder __h = __construct_node(std::move(__value));
    __node_insert_unique(__h.get());
    __h.release();
  }

  template <class _ValueT = _Tp, __enable_if_t<__is_hash_value_type<_ValueT>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void __insert_multi_from_orphaned_node(value_type&& __value) {
    __node_holder __h = __construct_node(const_cast<key_type&&>(__value.first), std::move(__value.second));
    __node_insert_multi(__h.get());
    __h.release();
  }

  template <class _ValueT = _Tp, __enable_if_t<!__is_hash_value_type<_ValueT>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void __insert_multi_from_orphaned_node(value_type&& __value) {
    __node_holder __h = __construct_node(std::move(__value));
    __node_insert_multi(__h.get());
    __h.release();
  }

#if _LIBCPP_STD_VER >= 17
  template <class _NodeHandle, class _InsertReturnType>
  _LIBCPP_HIDE_FROM_ABI _InsertReturnType __node_handle_insert_unique(_NodeHandle&& __nh);
  template <class _NodeHandle>
  _LIBCPP_HIDE_FROM_ABI iterator __node_handle_insert_unique(const_iterator __hint, _NodeHandle&& __nh);
  template <class _Table>
  _LIBCPP_HIDE_FROM_ABI void __node_handle_merge_unique(_Table& __source);

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

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

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

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

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

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

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

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

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

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

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

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

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

  _LIBCPP_HIDE_FROM_ABI size_type max_bucket_count() const _NOEXCEPT { return max_size(); }
  _LIBCPP_HIDE_FROM_ABI size_type bucket_size(size_type __n) const;
  _LIBCPP_HIDE_FROM_ABI float load_factor() const _NOEXCEPT {
    size_type __bc = bucket_count();
    return __bc != 0 ? (float)size() / __bc : 0.f;
  }
  _LIBCPP_HIDE_FROM_ABI void max_load_factor(float __mlf) _NOEXCEPT {
    // While passing a non-positive load factor is undefined behavior, in practice the result will be benign (the
    // call will be equivalent to `max_load_factor(load_factor())`, which is also the case for passing a valid value
    // less than the current `load_factor`).
    _LIBCPP_ASSERT_PEDANTIC(__mlf > 0, "unordered container::max_load_factor(lf) called with lf <= 0");
    max_load_factor() = std::max(__mlf, load_factor());
  }

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

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

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

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

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

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

  template <class... _Args>
  _LIBCPP_HIDE_FROM_ABI __node_holder __construct_node_hash(size_t __hash, _Args&&... __args);

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

  _LIBCPP_HIDE_FROM_ABI void __move_assign(__hash_table& __u, false_type);
  _LIBCPP_HIDE_FROM_ABI 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_HIDE_FROM_ABI 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_HIDE_FROM_ABI 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() = std::move(__u.__bucket_list_.get_deleter().__alloc());
    __node_alloc()                         = std::move(__u.__node_alloc());
  }
  _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(__hash_table&, false_type) _NOEXCEPT {}

  _LIBCPP_HIDE_FROM_ABI void __deallocate_node(__node_pointer __nd) _NOEXCEPT {
    auto& __alloc = __node_alloc();
    __node_traits::destroy(__alloc, std::addressof(__nd->__get_value()));
    std::__destroy_at(std::__to_address(__nd));
    __node_traits::deallocate(__alloc, __nd, 1);
  }

  _LIBCPP_HIDE_FROM_ABI void __deallocate_node_list(__next_pointer __np) _NOEXCEPT {
    while (__np != nullptr) {
      __next_pointer __next = __np->__next_;
      __deallocate_node(__np->__upcast());
      __np = __next;
    }
  }

  _LIBCPP_HIDE_FROM_ABI __next_pointer __detach() _NOEXCEPT;

  template <class _From, class _ValueT = _Tp, __enable_if_t<__is_hash_value_type<_ValueT>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void __assign_value(__get_hash_node_value_type_t<_Tp>& __lhs, _From&& __rhs) {
    // This is technically UB, since the object was constructed as `const`.
    // Clang doesn't optimize on this currently though.
    const_cast<key_type&>(__lhs.first) = const_cast<__copy_cvref_t<_From, key_type>&&>(__rhs.first);
    __lhs.second                       = std::forward<_From>(__rhs).second;
  }

  template <class _From, class _ValueT = _Tp, __enable_if_t<!__is_hash_value_type<_ValueT>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI void __assign_value(_Tp& __lhs, _From&& __rhs) {
    __lhs = std::forward<_From>(__rhs);
  }

  template <class, class, class, class, class>
  friend class unordered_map;
  template <class, class, class, class, class>
  friend class 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)
    : __size_(0), __max_load_factor_(1.0f) {}

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()),
      __first_node_(),
      __node_alloc_(),
      __size_(0),
      __hasher_(__hf),
      __max_load_factor_(1.0f),
      __key_eq_(__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)),
      __node_alloc_(__node_allocator(__a)),
      __size_(0),
      __hasher_(__hf),
      __max_load_factor_(1.0f),
      __key_eq_(__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)),
      __node_alloc_(__node_allocator(__a)),
      __size_(0),
      __max_load_factor_(1.0f) {}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
__hash_table<_Tp, _Hash, _Equal, _Alloc>::__hash_table(const __hash_table& __other)
    : __bucket_list_(nullptr,
                     __bucket_list_deleter(__pointer_alloc_traits::select_on_container_copy_construction(
                                               __other.__bucket_list_.get_deleter().__alloc()),
                                           0)),
      __node_alloc_(__node_traits::select_on_container_copy_construction(__other.__node_alloc())),
      __size_(0),
      __hasher_(__other.hash_function()),
      __max_load_factor_(__other.__max_load_factor_),
      __key_eq_(__other.__key_eq_) {
  if (__other.size() == 0)
    return;

  auto& __bucket_list_del = __bucket_list_.get_deleter();
  auto __bucket_count     = __other.bucket_count();
  __bucket_list_.reset(__pointer_alloc_traits::allocate(__bucket_list_del.__alloc(), __bucket_count));
  __bucket_list_del.size() = __bucket_count;

  std::fill_n(__bucket_list_.get(), __bucket_count, nullptr);

  __copy_construct(__other.__first_node_.__next_);
  __size_ = __other.size();
}

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)),
      __node_alloc_(__node_allocator(__a)),
      __size_(0),
      __hasher_(__u.hash_function()),
      __max_load_factor_(__u.__max_load_factor_),
      __key_eq_(__u.__key_eq_) {}

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_(std::move(__u.__bucket_list_)),
      __first_node_(std::move(__u.__first_node_)),
      __node_alloc_(std::move(__u.__node_alloc_)),
      __size_(std::move(__u.__size_)),
      __hasher_(std::move(__u.__hasher_)),
      __max_load_factor_(__u.__max_load_factor_),
      __key_eq_(std::move(__u.__key_eq_)) {
  if (size() > 0) {
    __bucket_list_[std::__constrain_hash(__first_node_.__next_->__hash(), bucket_count())] = __first_node_.__ptr();
    __u.__first_node_.__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)),
      __node_alloc_(__node_allocator(__a)),
      __size_(0),
      __hasher_(std::move(__u.__hasher_)),
      __max_load_factor_(__u.__max_load_factor_),
      __key_eq_(std::move(__u.__key_eq_)) {
  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) {
      __first_node_.__next_     = __u.__first_node_.__next_;
      __u.__first_node_.__next_ = nullptr;
      __bucket_list_[std::__constrain_hash(__first_node_.__next_->__hash(), bucket_count())] = __first_node_.__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_list(__first_node_.__next_);
}

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& __other) {
  if (this == std::addressof(__other))
    return *this;

  __copy_assign_alloc(__other);
  hash_function()   = __other.hash_function();
  key_eq()          = __other.key_eq();
  max_load_factor() = __other.max_load_factor();

  if (__other.size() == 0) {
    clear();
    return *this;
  }

  auto __bucket_count = __other.bucket_count();
  if (__bucket_count != bucket_count()) {
    auto& __bucket_list_del = __bucket_list_.get_deleter();
    __bucket_list_.reset(__pointer_alloc_traits::allocate(__bucket_list_del.__alloc(), __bucket_count));
    __bucket_list_del.size() = __bucket_count;
  }
  std::fill_n(__bucket_list_.get(), __bucket_count, nullptr);

  if (!__first_node_.__next_) {
    __copy_construct(__other.__first_node_.__next_);
    __size_ = __other.size();
    return *this;
  }

  __next_pointer __other_iter = __other.__first_node_.__next_;
  __next_pointer __own_iter   = __first_node_.__ptr();
  {
    __node_pointer __next = __own_iter->__next_->__upcast();
    __assign_value(__next->__get_value(), __other_iter->__upcast()->__get_value());
    __next->__hash_ = __other_iter->__hash();
  }
  size_t __current_chash          = std::__constrain_hash(__own_iter->__next_->__hash(), __bucket_count);
  __bucket_list_[__current_chash] = __own_iter;
  __other_iter                    = __other_iter->__next_;
  __own_iter                      = __own_iter->__next_;

  // Go through the nodes of the incoming hash table and copy then into the destination hash table, reusing as many
  // existing nodes as posssible in the destination.
  while (__other_iter && __own_iter->__next_) {
    __node_pointer __next = __own_iter->__next_->__upcast();
    __assign_value(__next->__get_value(), __other_iter->__upcast()->__get_value());
    __next->__hash_ = __other_iter->__hash();

    size_t __new_chash = std::__constrain_hash(__next->__hash_, __bucket_count);
    if (__new_chash != __current_chash) {
      __bucket_list_[__new_chash] = __own_iter;
      __current_chash             = __new_chash;
    }

    __other_iter = __other_iter->__next_;
    __own_iter   = __own_iter->__next_;
  }

  // At this point we either have consumed the whole incoming hash table, or we don't have any more nodes to reuse in
  // the destination. Either continue with constructing new nodes, or deallocate the left over nodes.
  if (__own_iter->__next_) {
    __deallocate_node_list(__own_iter->__next_);
    __own_iter->__next_ = nullptr;
  } else {
    __copy_construct(__other_iter, __own_iter, __current_chash);
  }

  __size_ = __other.size();

  return *this;
}

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 = __first_node_.__next_;
  __first_node_.__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()       = std::move(__u.hash_function());
  max_load_factor()     = __u.max_load_factor();
  key_eq()              = std::move(__u.key_eq());
  __first_node_.__next_ = __u.__first_node_.__next_;
  if (size() > 0) {
    __bucket_list_[std::__constrain_hash(__first_node_.__next_->__hash(), bucket_count())] = __first_node_.__ptr();
    __u.__first_node_.__next_                                                              = nullptr;
    __u.size()                                                                             = 0;
  }
}

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()   = std::move(__u.hash_function());
    key_eq()          = std::move(__u.key_eq());
    max_load_factor() = __u.max_load_factor();
    if (bucket_count() != 0) {
      __next_pointer __cache = __detach();
      auto __guard           = std::__make_scope_guard([&] { __deallocate_node_list(__cache); });
      const_iterator __i     = __u.begin();
      while (__cache != nullptr && __u.size() != 0) {
        __assign_value(__cache->__upcast()->__get_value(), std::move(__u.remove(__i++)->__get_value()));
        __next_pointer __next = __cache->__next_;
        __node_insert_multi(__cache->__upcast());
        __cache = __next;
      }
    }
    const_iterator __i = __u.begin();
    while (__u.size() != 0)
      __insert_multi_from_orphaned_node(std::move(__u.remove(__i++)->__get_value()));
  }
}

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_(is_nothrow_move_assignable<hasher>::value&& is_nothrow_move_assignable<key_equal>::value &&
               ((__node_traits::propagate_on_container_move_assignment::value &&
                 is_nothrow_move_assignable<__node_allocator>::value) ||
                allocator_traits<__node_allocator>::is_always_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, value_type>::value, "__assign_unique may only be called with the containers value type");

  if (bucket_count() != 0) {
    __next_pointer __cache = __detach();
    auto __guard           = std::__make_scope_guard([&] { __deallocate_node_list(__cache); });
    for (; __cache != nullptr && __first != __last; ++__first) {
      __assign_value(__cache->__upcast()->__get_value(), *__first);
      __next_pointer __next = __cache->__next_;
      __node_insert_unique(__cache->__upcast());
      __cache = __next;
    }
  }
  for (; __first != __last; ++__first)
    __emplace_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, 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();
    auto __guard           = std::__make_scope_guard([&] { __deallocate_node_list(__cache); });
    for (; __cache != nullptr && __first != __last; ++__first) {
      __assign_value(__cache->__upcast()->__get_value(), *__first);
      __next_pointer __next = __cache->__next_;
      __node_insert_multi(__cache->__upcast());
      __cache = __next;
    }
  }
  for (; __first != __last; ++__first)
    __emplace_multi(*__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(__first_node_.__next_);
}

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);
}

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(__first_node_.__next_);
}

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);
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
void __hash_table<_Tp, _Hash, _Equal, _Alloc>::clear() _NOEXCEPT {
  if (size() > 0) {
    __deallocate_node_list(__first_node_.__next_);
    __first_node_.__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_HIDE_FROM_ABI 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 &&
           (__ndptr->__hash() == __hash || std::__constrain_hash(__ndptr->__hash(), __bc) == __chash);
           __ndptr = __ndptr->__next_) {
        if ((__ndptr->__hash() == __hash) && key_eq()(__ndptr->__upcast()->__get_value(), __value))
          return __ndptr;
      }
    }
  }
  if (size() + 1 > __bc * max_load_factor() || __bc == 0) {
    __rehash_unique(std::max<size_type>(
        2 * __bc + !std::__is_hash_power2(__bc), size_type(__math::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_HIDE_FROM_ABI 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          = __first_node_.__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->__get_value());
  __next_pointer __existing_node = __node_insert_unique_prepare(__nd->__hash(), __nd->__get_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), __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(std::max<size_type>(
        2 * __bc + !std::__is_hash_power2(__bc), size_type(__math::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()->__get_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          = __first_node_.__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->__get_value());
  __next_pointer __pn = __node_insert_multi_prepare(__cp->__hash(), __cp->__get_value());
  __node_insert_multi_perform(__cp, __pn);

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

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) {
  if (__p != end() && key_eq()(*__p, __cp->__get_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(std::max<size_type>(
          2 * __bc + !std::__is_hash_power2(__bc), size_type(__math::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));
  }
  return __node_insert_multi(__cp);
}

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(std::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) {
  __node_holder __h = __construct_node(std::forward<_Args>(__args)...);
  iterator __r      = __node_insert_multi(__p, __h.get());
  __h.release();
  return __r;
}

#if _LIBCPP_STD_VER >= 17
template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _NodeHandle, class _InsertReturnType>
_LIBCPP_HIDE_FROM_ABI _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, std::move(__nh)};
}

template <class _Tp, class _Hash, class _Equal, class _Alloc>
template <class _NodeHandle>
_LIBCPP_HIDE_FROM_ABI 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_HIDE_FROM_ABI _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_HIDE_FROM_ABI _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_HIDE_FROM_ABI 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->__get_value());
    __next_pointer __existing_node = __node_insert_unique_prepare(__hash, __src_ptr->__get_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_HIDE_FROM_ABI 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_HIDE_FROM_ABI 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_HIDE_FROM_ABI 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->__get_value());
    __next_pointer __pn      = __node_insert_multi_prepare(__src_hash, __src_ptr->__get_value());
    (void)__source.remove(__it++).release();
    __src_ptr->__hash_ = __src_hash;
    __node_insert_multi_perform(__src_ptr, __pn);
  }
}
#endif // _LIBCPP_STD_VER >= 17

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 = std::max<size_type>(
        __n,
        std::__is_hash_power2(__bc) ? std::__next_hash_pow2(size_t(__math::ceil(float(size()) / max_load_factor())))
                                    : std::__next_prime(size_t(__math::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 __bucket_count) {
  __pointer_allocator& __ptr_alloc = __bucket_list_.get_deleter().__alloc();
  __bucket_list_.reset(__bucket_count > 0 ? __pointer_alloc_traits::allocate(__ptr_alloc, __bucket_count) : nullptr);
  __bucket_list_.get_deleter().size() = __bucket_count;

  if (__bucket_count == 0)
    return;

  for (size_type __i = 0; __i < __bucket_count; ++__i)
    __bucket_list_[__i] = nullptr;
  __next_pointer __pp = __first_node_.__ptr();
  __next_pointer __cp = __pp->__next_;

  if (!__cp)
    return;

  size_type __chash       = std::__constrain_hash(__cp->__hash(), __bucket_count);
  __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(), __bucket_count);
    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 (!_UniqueKeys) {
          for (; __np->__next_ != nullptr &&
                 key_eq()(__cp->__upcast()->__get_value(), __np->__next_->__upcast()->__get_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_type __bc = bucket_count();
  if (__bc != 0 && size() != 0) {
    size_t __hash       = hash_function()(__k);
    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()->__get_value(), __k))
          return iterator(__nd);
      }
    }
  }
  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_type __bc = bucket_count();
  if (__bc != 0 && size() != 0) {
    size_t __hash       = hash_function()(__k);
    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()->__get_value(), __k))
          return const_iterator(__nd);
      }
    }
  }
  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));

  // Begin the lifetime of the node itself and the value_type contained within.
  //
  // We don't use the allocator's construct() method to construct the node itself since the
  // Cpp17FooInsertable named requirements don't require the allocator's construct() method
  // to work on anything other than the value_type.
  std::__construct_at(std::addressof(*__h), /* hash = */ 0, __na, std::forward<_Args>(__args)...);

  __h.get_deleter().__value_constructed = true;

  __h->__hash_ = hash_function()(__h->__get_value());
  return __h;
}

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_hash(size_t __hash, _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));
  std::__construct_at(std::addressof(*__h), /* hash = */ __hash, __na, std::forward<_Args>(__args)...);
  __h.get_deleter().__value_constructed = true;
  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_ASSERT_VALID_ELEMENT_ACCESS(
      __p != end(), "unordered container::erase(iterator) called with a non-dereferenceable iterator");
  iterator __r(__np);
  ++__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) {
  if (__first == __last)
    return iterator(__last.__node_);

  // current node
  __next_pointer __current = __first.__node_;
  size_type __bucket_count = bucket_count();
  size_t __chash           = std::__constrain_hash(__current->__hash(), __bucket_count);
  // find previous node
  __next_pointer __before_first = __bucket_list_[__chash];
  for (; __before_first->__next_ != __current; __before_first = __before_first->__next_)
    ;

  __next_pointer __last_node = __last.__node_;

  // If __before_first is in the same bucket (i.e. the first element we erase is not the first in the bucket), clear
  // this bucket first without re-linking it
  if (__before_first != __first_node_.__ptr() &&
      std::__constrain_hash(__before_first->__hash(), __bucket_count) == __chash) {
    while (__current != __last_node) {
      auto __next = __current->__next_;
      __deallocate_node(__current->__upcast());
      __current = __next;
      --__size_;

      if (__next) {
        if (auto __next_chash = std::__constrain_hash(__next->__hash(), __bucket_count); __next_chash != __chash) {
          __bucket_list_[__next_chash] = __before_first;
          __chash                      = __next_chash;
          break;
        }
      }
    }
  }

  while (__current != __last_node) {
    auto __next = __current->__next_;
    __deallocate_node(__current->__upcast());
    __current = __next;
    --__size_;

    // When switching buckets, set the old bucket to be empty and update the next bucket to have __before_first as its
    // before-first element
    if (__next) {
      if (auto __next_chash = std::__constrain_hash(__next->__hash(), __bucket_count); __next_chash != __chash) {
        __bucket_list_[__chash]      = nullptr;
        __bucket_list_[__next_chash] = __before_first;
        __chash                      = __next_chash;
      }
    } else { // When __next is a nullptr we've fully erased the last bucket. Update the bucket list accordingly.
      __bucket_list_[__chash] = nullptr;
    }
  }

  // re-link __before_first with __last
  __before_first->__next_ = __current;

  return iterator(__last.__node_);
}

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 == __first_node_.__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();
  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_v<hasher>&& __is_nothrow_swappable_v<key_equal> &&
               (!allocator_traits<__pointer_allocator>::propagate_on_container_swap::value ||
                __is_nothrow_swappable_v<__pointer_allocator>) &&
               (!__node_traits::propagate_on_container_swap::value || __is_nothrow_swappable_v<__node_allocator>))
#else
    _NOEXCEPT_(__is_nothrow_swappable_v<hasher>&& __is_nothrow_swappable_v<key_equal>)
#endif
{
  _LIBCPP_ASSERT_COMPATIBLE_ALLOCATOR(
      __node_traits::propagate_on_container_swap::value || this->__node_alloc() == __u.__node_alloc(),
      "unordered container::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);
  }
  std::swap(__bucket_list_.get_deleter().size(), __u.__bucket_list_.get_deleter().size());
  std::__swap_allocator(__bucket_list_.get_deleter().__alloc(), __u.__bucket_list_.get_deleter().__alloc());
  std::__swap_allocator(__node_alloc(), __u.__node_alloc());
  std::swap(__first_node_.__next_, __u.__first_node_.__next_);
  using std::swap;
  swap(__size_, __u.__size_);
  swap(__hasher_, __u.__hasher_);
  swap(__max_load_factor_, __u.__max_load_factor_);
  swap(__key_eq_, __u.__key_eq_);
  if (size() > 0)
    __bucket_list_[std::__constrain_hash(__first_node_.__next_->__hash(), bucket_count())] = __first_node_.__ptr();
  if (__u.size() > 0)
    __u.__bucket_list_[std::__constrain_hash(__u.__first_node_.__next_->__hash(), __u.bucket_count())] =
        __u.__first_node_.__ptr();
}

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_VALID_ELEMENT_ACCESS(
      __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_HIDE_FROM_ABI void
swap(__hash_table<_Tp, _Hash, _Equal, _Alloc>& __x, __hash_table<_Tp, _Hash, _Equal, _Alloc>& __y)
    _NOEXCEPT_(_NOEXCEPT_(__x.swap(__y))) {
  __x.swap(__y);
}

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___HASH_TABLE