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// hashtable.h header -*- C++ -*-

// Copyright (C) 2007-2015 Free Software Foundation, Inc.

//

// This file is part of the GNU ISO C++ Library.  This library is free

// software; you can redistribute it and/or modify it under the

// terms of the GNU General Public License as published by the

// Free Software Foundation; either version 3, or (at your option)

// any later version.

// This library is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional

// permissions described in the GCC Runtime Library Exception, version

// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and

// a copy of the GCC Runtime Library Exception along with this program;

// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see

// .

/** @file bits/hashtable.h

 *  This is an internal header file, included by other library headers.

 *  Do not attempt to use it directly. @headername{unordered_map, unordered_set}

 */

#ifndef _HASHTABLE_H

#define _HASHTABLE_H 1

#pragma GCC system_header

#include 

namespace std _GLIBCXX_VISIBILITY(default)

{

_GLIBCXX_BEGIN_NAMESPACE_VERSION

  template

    using __cache_default

      =  __not_<__and_

		       __is_fast_hash<_Hash>,

		       // Mandatory to have erase not throwing.

		       __detail::__is_noexcept_hash<_Tp, _Hash>>>;

  /**

   *  Primary class template _Hashtable.

   *

   *  @ingroup hashtable-detail

   *

   *  @tparam _Value  CopyConstructible type.

   *

   *  @tparam _Key    CopyConstructible type.

   *

   *  @tparam _Alloc  An allocator type

   *  ([lib.allocator.requirements]) whose _Alloc::value_type is

   *  _Value.  As a conforming extension, we allow for

   *  _Alloc::value_type != _Value.

   *

   *  @tparam _ExtractKey  Function object that takes an object of type

   *  _Value and returns a value of type _Key.

   *

   *  @tparam _Equal  Function object that takes two objects of type k

   *  and returns a bool-like value that is true if the two objects

   *  are considered equal.

   *

   *  @tparam _H1  The hash function. A unary function object with

   *  argument type _Key and result type size_t. Return values should

   *  be distributed over the entire range [0, numeric_limits:::max()].

   *

   *  @tparam _H2  The range-hashing function (in the terminology of

   *  Tavori and Dreizin).  A binary function object whose argument

   *  types and result type are all size_t.  Given arguments r and N,

   *  the return value is in the range [0, N).

   *

   *  @tparam _Hash  The ranged hash function (Tavori and Dreizin). A

   *  binary function whose argument types are _Key and size_t and

   *  whose result type is size_t.  Given arguments k and N, the

   *  return value is in the range [0, N).  Default: hash(k, N) =

   *  h2(h1(k), N).  If _Hash is anything other than the default, _H1

   *  and _H2 are ignored.

   *

   *  @tparam _RehashPolicy  Policy class with three members, all of

   *  which govern the bucket count. _M_next_bkt(n) returns a bucket

   *  count no smaller than n.  _M_bkt_for_elements(n) returns a

   *  bucket count appropriate for an element count of n.

   *  _M_need_rehash(n_bkt, n_elt, n_ins) determines whether, if the

   *  current bucket count is n_bkt and the current element count is

   *  n_elt, we need to increase the bucket count.  If so, returns

   *  make_pair(true, n), where n is the new bucket count.  If not,

   *  returns make_pair(false, )

   *

   *  @tparam _Traits  Compile-time class with three boolean

   *  std::integral_constant members:  __cache_hash_code, __constant_iterators,

   *   __unique_keys.

   *

   *  Each _Hashtable data structure has:

   *

   *  - _Bucket[]       _M_buckets

   *  - _Hash_node_base _M_before_begin

   *  - size_type       _M_bucket_count

   *  - size_type       _M_element_count

   *

   *  with _Bucket being _Hash_node* and _Hash_node containing:

   *

   *  - _Hash_node*   _M_next

   *  - Tp            _M_value

   *  - size_t        _M_hash_code if cache_hash_code is true

   *

   *  In terms of Standard containers the hashtable is like the aggregation of:

   *

   *  - std::forward_list<_Node> containing the elements

   *  - std::vector::iterator> representing the buckets

   *

   *  The non-empty buckets contain the node before the first node in the

   *  bucket. This design makes it possible to implement something like a

   *  std::forward_list::insert_after on container insertion and

   *  std::forward_list::erase_after on container erase

   *  calls. _M_before_begin is equivalent to

   *  std::forward_list::before_begin. Empty buckets contain

   *  nullptr.  Note that one of the non-empty buckets contains

   *  &_M_before_begin which is not a dereferenceable node so the

   *  node pointer in a bucket shall never be dereferenced, only its

   *  next node can be.

   *

   *  Walking through a bucket's nodes requires a check on the hash code to

   *  see if each node is still in the bucket. Such a design assumes a

   *  quite efficient hash functor and is one of the reasons it is

   *  highly advisable to set __cache_hash_code to true.

   *

   *  The container iterators are simply built from nodes. This way

   *  incrementing the iterator is perfectly efficient independent of

   *  how many empty buckets there are in the container.

   *

   *  On insert we compute the element's hash code and use it to find the

   *  bucket index. If the element must be inserted in an empty bucket

   *  we add it at the beginning of the singly linked list and make the

   *  bucket point to _M_before_begin. The bucket that used to point to

   *  _M_before_begin, if any, is updated to point to its new before

   *  begin node.

   *

   *  On erase, the simple iterator design requires using the hash

   *  functor to get the index of the bucket to update. For this

   *  reason, when __cache_hash_code is set to false the hash functor must

   *  not throw and this is enforced by a static assertion.

   *

   *  Functionality is implemented by decomposition into base classes,

   *  where the derived _Hashtable class is used in _Map_base,

   *  _Insert, _Rehash_base, and _Equality base classes to access the

   *  "this" pointer. _Hashtable_base is used in the base classes as a

   *  non-recursive, fully-completed-type so that detailed nested type

   *  information, such as iterator type and node type, can be

   *  used. This is similar to the "Curiously Recurring Template

   *  Pattern" (CRTP) technique, but uses a reconstructed, not

   *  explicitly passed, template pattern.

   *

   *  Base class templates are:

   *    - __detail::_Hashtable_base

   *    - __detail::_Map_base

   *    - __detail::_Insert

   *    - __detail::_Rehash_base

   *    - __detail::_Equality

   */

  template

	   typename _ExtractKey, typename _Equal,

	   typename _H1, typename _H2, typename _Hash,

	   typename _RehashPolicy, typename _Traits>

    class _Hashtable

    : public __detail::_Hashtable_base<_Key, _Value, _ExtractKey, _Equal,

				       _H1, _H2, _Hash, _Traits>,

      public __detail::_Map_base<_Key, _Value, _Alloc, _ExtractKey, _Equal,

				 _H1, _H2, _Hash, _RehashPolicy, _Traits>,

      public __detail::_Insert<_Key, _Value, _Alloc, _ExtractKey, _Equal,

			       _H1, _H2, _Hash, _RehashPolicy, _Traits>,

      public __detail::_Rehash_base<_Key, _Value, _Alloc, _ExtractKey, _Equal,

				    _H1, _H2, _Hash, _RehashPolicy, _Traits>,

      public __detail::_Equality<_Key, _Value, _Alloc, _ExtractKey, _Equal,

				 _H1, _H2, _Hash, _RehashPolicy, _Traits>,

      private __detail::_Hashtable_alloc<

	typename __alloctr_rebind<_Alloc,

	  __detail::_Hash_node<_Value,

			       _Traits::__hash_cached::value> >::__type>

    {

      using __traits_type = _Traits;

      using __hash_cached = typename __traits_type::__hash_cached;

      using __node_type = __detail::_Hash_node<_Value, __hash_cached::value>;

      using __node_alloc_type =

	typename __alloctr_rebind<_Alloc, __node_type>::__type;

      using __hashtable_alloc = __detail::_Hashtable_alloc<__node_alloc_type>;

      using __value_alloc_traits =

	typename __hashtable_alloc::__value_alloc_traits;

      using __node_alloc_traits =

	typename __hashtable_alloc::__node_alloc_traits;

      using __node_base = typename __hashtable_alloc::__node_base;

      using __bucket_type = typename __hashtable_alloc::__bucket_type;

    public:

      typedef _Key						key_type;

      typedef _Value						value_type;

      typedef _Alloc						allocator_type;

      typedef _Equal						key_equal;

      // mapped_type, if present, comes from _Map_base.

      // hasher, if present, comes from _Hash_code_base/_Hashtable_base.

      typedef typename __value_alloc_traits::pointer		pointer;

      typedef typename __value_alloc_traits::const_pointer	const_pointer;

      typedef value_type&					reference;

      typedef const value_type&					const_reference;

    private:

      using __rehash_type = _RehashPolicy;

      using __rehash_state = typename __rehash_type::_State;

      using __constant_iterators = typename __traits_type::__constant_iterators;

      using __unique_keys = typename __traits_type::__unique_keys;

      using __key_extract = typename std::conditional<

					     __constant_iterators::value,

				       	     __detail::_Identity,

					     __detail::_Select1st>::type;

      using __hashtable_base = __detail::

			       _Hashtable_base<_Key, _Value, _ExtractKey,

					      _Equal, _H1, _H2, _Hash, _Traits>;

      using __hash_code_base =  typename __hashtable_base::__hash_code_base;

      using __hash_code =  typename __hashtable_base::__hash_code;

      using __ireturn_type = typename __hashtable_base::__ireturn_type;

      using __map_base = __detail::_Map_base<_Key, _Value, _Alloc, _ExtractKey,

					     _Equal, _H1, _H2, _Hash,

					     _RehashPolicy, _Traits>;

      using __rehash_base = __detail::_Rehash_base<_Key, _Value, _Alloc,

						   _ExtractKey, _Equal,

						   _H1, _H2, _Hash,

						   _RehashPolicy, _Traits>;

      using __eq_base = __detail::_Equality<_Key, _Value, _Alloc, _ExtractKey,

					    _Equal, _H1, _H2, _Hash,

					    _RehashPolicy, _Traits>;

      using __reuse_or_alloc_node_type =

	__detail::_ReuseOrAllocNode<__node_alloc_type>;

      // Metaprogramming for picking apart hash caching.

      template

	using __if_hash_cached = __or_<__not_<__hash_cached>, _Cond>;

      template

	using __if_hash_not_cached = __or_<__hash_cached, _Cond>;

      // Compile-time diagnostics.

      // _Hash_code_base has everything protected, so use this derived type to

      // access it.

      struct __hash_code_base_access : __hash_code_base

      { using __hash_code_base::_M_bucket_index; };

      // Getting a bucket index from a node shall not throw because it is used

      // in methods (erase, swap...) that shall not throw.

      static_assert(noexcept(declval()

			     ._M_bucket_index((const __node_type*)nullptr,

					      (std::size_t)0)),

		    "Cache the hash code or qualify your functors involved"

		    " in hash code and bucket index computation with noexcept");

      // Following two static assertions are necessary to guarantee

      // that local_iterator will be default constructible.

      // When hash codes are cached local iterator inherits from H2 functor

      // which must then be default constructible.

      static_assert(__if_hash_cached>::value,

		    "Functor used to map hash code to bucket index"

		    " must be default constructible");

      template

	       typename _ExtractKeya, typename _Equala,

	       typename _H1a, typename _H2a, typename _Hasha,

	       typename _RehashPolicya, typename _Traitsa,

	       bool _Unique_keysa>

	friend struct __detail::_Map_base;

      template

	       typename _ExtractKeya, typename _Equala,

	       typename _H1a, typename _H2a, typename _Hasha,

	       typename _RehashPolicya, typename _Traitsa>

	friend struct __detail::_Insert_base;

      template

	       typename _ExtractKeya, typename _Equala,

	       typename _H1a, typename _H2a, typename _Hasha,

	       typename _RehashPolicya, typename _Traitsa,

	       bool _Constant_iteratorsa, bool _Unique_keysa>

	friend struct __detail::_Insert;

    public:

      using size_type = typename __hashtable_base::size_type;

      using difference_type = typename __hashtable_base::difference_type;

      using iterator = typename __hashtable_base::iterator;

      using const_iterator = typename __hashtable_base::const_iterator;

      using local_iterator = typename __hashtable_base::local_iterator;

      using const_local_iterator = typename __hashtable_base::

				   const_local_iterator;

    private:

      __bucket_type*		_M_buckets		= &_M_single_bucket;

      size_type			_M_bucket_count		= 1;

      __node_base		_M_before_begin;

      size_type			_M_element_count	= 0;

      _RehashPolicy		_M_rehash_policy;

      // A single bucket used when only need for 1 bucket. Especially

      // interesting in move semantic to leave hashtable with only 1 buckets

      // which is not allocated so that we can have those operations noexcept

      // qualified.

      // Note that we can't leave hashtable with 0 bucket without adding

      // numerous checks in the code to avoid 0 modulus.

      __bucket_type		_M_single_bucket	= nullptr;

      bool

      _M_uses_single_bucket(__bucket_type* __bkts) const

      { return __builtin_expect(__bkts == &_M_single_bucket, false); }

      bool

      _M_uses_single_bucket() const

      { return _M_uses_single_bucket(_M_buckets); }

      __hashtable_alloc&

      _M_base_alloc() { return *this; }

      __bucket_type*

      _M_allocate_buckets(size_type __n)

      {

	if (__builtin_expect(__n == 1, false))

	  {

	    _M_single_bucket = nullptr;

	    return &_M_single_bucket;

	  }

	return __hashtable_alloc::_M_allocate_buckets(__n);

      }

      void

      _M_deallocate_buckets(__bucket_type* __bkts, size_type __n)

      {

	if (_M_uses_single_bucket(__bkts))

	  return;

	__hashtable_alloc::_M_deallocate_buckets(__bkts, __n);

      }

      void

      _M_deallocate_buckets()

      { _M_deallocate_buckets(_M_buckets, _M_bucket_count); }

      // Gets bucket begin, deals with the fact that non-empty buckets contain

      // their before begin node.

      __node_type*

      _M_bucket_begin(size_type __bkt) const;

      __node_type*

      _M_begin() const

      { return static_cast<__node_type*>(_M_before_begin._M_nxt); }

      template

	void

	_M_assign(const _Hashtable&, const _NodeGenerator&);

      void

      _M_move_assign(_Hashtable&&, std::true_type);

      void

      _M_move_assign(_Hashtable&&, std::false_type);

      void

      _M_reset() noexcept;

      _Hashtable(const _H1& __h1, const _H2& __h2, const _Hash& __h,

		 const _Equal& __eq, const _ExtractKey& __exk,

		 const allocator_type& __a)

	: __hashtable_base(__exk, __h1, __h2, __h, __eq),

	  __hashtable_alloc(__node_alloc_type(__a))

      { }

    public:

      // Constructor, destructor, assignment, swap

      _Hashtable() = default;

      _Hashtable(size_type __bucket_hint,

		 const _H1&, const _H2&, const _Hash&,

		 const _Equal&, const _ExtractKey&,

		 const allocator_type&);

      template

	_Hashtable(_InputIterator __first, _InputIterator __last,

		   size_type __bucket_hint,

		   const _H1&, const _H2&, const _Hash&,

		   const _Equal&, const _ExtractKey&,

		   const allocator_type&);

      _Hashtable(const _Hashtable&);

      _Hashtable(_Hashtable&&) noexcept;

      _Hashtable(const _Hashtable&, const allocator_type&);

      _Hashtable(_Hashtable&&, const allocator_type&);

      // Use delegating constructors.

      explicit

      _Hashtable(const allocator_type& __a)

	: __hashtable_alloc(__node_alloc_type(__a))

      { }

      explicit

      _Hashtable(size_type __n,

		 const _H1& __hf = _H1(),

		 const key_equal& __eql = key_equal(),

		 const allocator_type& __a = allocator_type())

      : _Hashtable(__n, __hf, _H2(), _Hash(), __eql,

		   __key_extract(), __a)

      { }

      template

	_Hashtable(_InputIterator __f, _InputIterator __l,

		   size_type __n = 0,

		   const _H1& __hf = _H1(),

		   const key_equal& __eql = key_equal(),

		   const allocator_type& __a = allocator_type())

	: _Hashtable(__f, __l, __n, __hf, _H2(), _Hash(), __eql,

		     __key_extract(), __a)

	{ }

      _Hashtable(initializer_list __l,

		 size_type __n = 0,

		 const _H1& __hf = _H1(),

		 const key_equal& __eql = key_equal(),

		 const allocator_type& __a = allocator_type())

      : _Hashtable(__l.begin(), __l.end(), __n, __hf, _H2(), _Hash(), __eql,

		   __key_extract(), __a)

      { }

      _Hashtable&

      operator=(const _Hashtable& __ht);

      _Hashtable&

      operator=(_Hashtable&& __ht)

      noexcept(__node_alloc_traits::_S_nothrow_move())

      {

        constexpr bool __move_storage =

          __node_alloc_traits::_S_propagate_on_move_assign()

          || __node_alloc_traits::_S_always_equal();

        _M_move_assign(std::move(__ht),

                       integral_constant());

	return *this;

      }

      _Hashtable&

      operator=(initializer_list __l)

      {

	__reuse_or_alloc_node_type __roan(_M_begin(), *this);

	_M_before_begin._M_nxt = nullptr;

	clear();

	this->_M_insert_range(__l.begin(), __l.end(), __roan);

	return *this;

      }

      ~_Hashtable() noexcept;

      void

      swap(_Hashtable&)

      noexcept(__node_alloc_traits::_S_nothrow_swap());

      // Basic container operations

      iterator

      begin() noexcept

      { return iterator(_M_begin()); }

      const_iterator

      begin() const noexcept

      { return const_iterator(_M_begin()); }

      iterator

      end() noexcept

      { return iterator(nullptr); }

      const_iterator

      end() const noexcept

      { return const_iterator(nullptr); }

      const_iterator

      cbegin() const noexcept

      { return const_iterator(_M_begin()); }

      const_iterator

      cend() const noexcept

      { return const_iterator(nullptr); }

      size_type

      size() const noexcept

      { return _M_element_count; }

      bool

      empty() const noexcept

      { return size() == 0; }

      allocator_type

      get_allocator() const noexcept

      { return allocator_type(this->_M_node_allocator()); }

      size_type

      max_size() const noexcept

      { return __node_alloc_traits::max_size(this->_M_node_allocator()); }

      // Observers

      key_equal

      key_eq() const

      { return this->_M_eq(); }

      // hash_function, if present, comes from _Hash_code_base.

      // Bucket operations

      size_type

      bucket_count() const noexcept

      { return _M_bucket_count; }

      size_type

      max_bucket_count() const noexcept

      { return max_size(); }

      size_type

      bucket_size(size_type __n) const

      { return std::distance(begin(__n), end(__n)); }

      size_type

      bucket(const key_type& __k) const

      { return _M_bucket_index(__k, this->_M_hash_code(__k)); }

      local_iterator

      begin(size_type __n)

      {

	return local_iterator(*this, _M_bucket_begin(__n),

			      __n, _M_bucket_count);

      }

      local_iterator

      end(size_type __n)

      { return local_iterator(*this, nullptr, __n, _M_bucket_count); }

      const_local_iterator

      begin(size_type __n) const

      {

	return const_local_iterator(*this, _M_bucket_begin(__n),

				    __n, _M_bucket_count);

      }

      const_local_iterator

      end(size_type __n) const

      { return const_local_iterator(*this, nullptr, __n, _M_bucket_count); }

      // DR 691.

      const_local_iterator

      cbegin(size_type __n) const

      {

	return const_local_iterator(*this, _M_bucket_begin(__n),

				    __n, _M_bucket_count);

      }

      const_local_iterator

      cend(size_type __n) const

      { return const_local_iterator(*this, nullptr, __n, _M_bucket_count); }

      float

      load_factor() const noexcept

      {

	return static_cast(size()) / static_cast(bucket_count());

      }

      // max_load_factor, if present, comes from _Rehash_base.

      // Generalization of max_load_factor.  Extension, not found in

      // TR1.  Only useful if _RehashPolicy is something other than

      // the default.

      const _RehashPolicy&

      __rehash_policy() const

      { return _M_rehash_policy; }

      void

      __rehash_policy(const _RehashPolicy&);

      // Lookup.

      iterator

      find(const key_type& __k);

      const_iterator

      find(const key_type& __k) const;

      size_type

      count(const key_type& __k) const;

      std::pair

      equal_range(const key_type& __k);

      std::pair

      equal_range(const key_type& __k) const;

    protected:

      // Bucket index computation helpers.

      size_type

      _M_bucket_index(__node_type* __n) const noexcept

      { return __hash_code_base::_M_bucket_index(__n, _M_bucket_count); }

      size_type

      _M_bucket_index(const key_type& __k, __hash_code __c) const

      { return __hash_code_base::_M_bucket_index(__k, __c, _M_bucket_count); }

      // Find and insert helper functions and types

      // Find the node before the one matching the criteria.

      __node_base*

      _M_find_before_node(size_type, const key_type&, __hash_code) const;

      __node_type*

      _M_find_node(size_type __bkt, const key_type& __key,

		   __hash_code __c) const

      {

	__node_base* __before_n = _M_find_before_node(__bkt, __key, __c);

	if (__before_n)

	  return static_cast<__node_type*>(__before_n->_M_nxt);

	return nullptr;

      }

      // Insert a node at the beginning of a bucket.

      void

      _M_insert_bucket_begin(size_type, __node_type*);

      // Remove the bucket first node

      void

      _M_remove_bucket_begin(size_type __bkt, __node_type* __next_n,

			     size_type __next_bkt);

      // Get the node before __n in the bucket __bkt

      __node_base*

      _M_get_previous_node(size_type __bkt, __node_base* __n);

      // Insert node with hash code __code, in bucket bkt if no rehash (assumes

      // no element with its key already present). Take ownership of the node,

      // deallocate it on exception.

      iterator

      _M_insert_unique_node(size_type __bkt, __hash_code __code,

			    __node_type* __n);

      // Insert node with hash code __code. Take ownership of the node,

      // deallocate it on exception.

      iterator

      _M_insert_multi_node(__node_type* __hint,

			   __hash_code __code, __node_type* __n);

      template

	std::pair

	_M_emplace(std::true_type, _Args&&... __args);

      template

	iterator

	_M_emplace(std::false_type __uk, _Args&&... __args)

	{ return _M_emplace(cend(), __uk, std::forward<_Args>(__args)...); }

      // Emplace with hint, useless when keys are unique.

      template

	iterator

	_M_emplace(const_iterator, std::true_type __uk, _Args&&... __args)

	{ return _M_emplace(__uk, std::forward<_Args>(__args)...).first; }

      template

	iterator

	_M_emplace(const_iterator, std::false_type, _Args&&... __args);

      template

	std::pair

	_M_insert(_Arg&&, const _NodeGenerator&, std::true_type);

      template

	iterator

	_M_insert(_Arg&& __arg, const _NodeGenerator& __node_gen,

		  std::false_type __uk)

	{

	  return _M_insert(cend(), std::forward<_Arg>(__arg), __node_gen,

			   __uk);

	}

      // Insert with hint, not used when keys are unique.

      template

	iterator

	_M_insert(const_iterator, _Arg&& __arg,

		  const _NodeGenerator& __node_gen, std::true_type __uk)

	{

	  return

	    _M_insert(std::forward<_Arg>(__arg), __node_gen, __uk).first;

	}

      // Insert with hint when keys are not unique.

      template

	iterator

	_M_insert(const_iterator, _Arg&&,

		  const _NodeGenerator&, std::false_type);

      size_type

      _M_erase(std::true_type, const key_type&);

      size_type

      _M_erase(std::false_type, const key_type&);

      iterator

      _M_erase(size_type __bkt, __node_base* __prev_n, __node_type* __n);

    public:

      // Emplace

      template

	__ireturn_type

	emplace(_Args&&... __args)

	{ return _M_emplace(__unique_keys(), std::forward<_Args>(__args)...); }

      template

	iterator

	emplace_hint(const_iterator __hint, _Args&&... __args)

	{

	  return _M_emplace(__hint, __unique_keys(),

			    std::forward<_Args>(__args)...);

	}

      // Insert member functions via inheritance.

      // Erase

      iterator

      erase(const_iterator);

      // LWG 2059.

      iterator

      erase(iterator __it)

      { return erase(const_iterator(__it)); }

      size_type

      erase(const key_type& __k)

      { return _M_erase(__unique_keys(), __k); }

      iterator

      erase(const_iterator, const_iterator);

      void

      clear() noexcept;

      // Set number of buckets to be appropriate for container of n element.

      void rehash(size_type __n);

      // DR 1189.

      // reserve, if present, comes from _Rehash_base.

    private:

      // Helper rehash method used when keys are unique.

      void _M_rehash_aux(size_type __n, std::true_type);

      // Helper rehash method used when keys can be non-unique.

      void _M_rehash_aux(size_type __n, std::false_type);

      // Unconditionally change size of bucket array to n, restore

      // hash policy state to __state on exception.

      void _M_rehash(size_type __n, const __rehash_state& __state);

    };

  // Definitions of class template _Hashtable's out-of-line member functions.

  template

	   typename _Alloc, typename _ExtractKey, typename _Equal,

	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,

	   typename _Traits>

    auto

    _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,

	       _H1, _H2, _Hash, _RehashPolicy, _Traits>::

    _M_bucket_begin(size_type __bkt) const

    -> __node_type*

    {

      __node_base* __n = _M_buckets[__bkt];

      return __n ? static_cast<__node_type*>(__n->_M_nxt) : nullptr;

    }

  template

	   typename _Alloc, typename _ExtractKey, typename _Equal,

	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,

	   typename _Traits>

    _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,

	       _H1, _H2, _Hash, _RehashPolicy, _Traits>::

    _Hashtable(size_type __bucket_hint,

	       const _H1& __h1, const _H2& __h2, const _Hash& __h,

	       const _Equal& __eq, const _ExtractKey& __exk,

	       const allocator_type& __a)

      : _Hashtable(__h1, __h2, __h, __eq, __exk, __a)

    {

      auto __bkt = _M_rehash_policy._M_next_bkt(__bucket_hint);

      if (__bkt > _M_bucket_count)

	{

	  _M_buckets = _M_allocate_buckets(__bkt);

	  _M_bucket_count = __bkt;

	}

    }

  template

	   typename _Alloc, typename _ExtractKey, typename _Equal,

	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,

	   typename _Traits>

    template

      _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,

		 _H1, _H2, _Hash, _RehashPolicy, _Traits>::

      _Hashtable(_InputIterator __f, _InputIterator __l,

		 size_type __bucket_hint,

		 const _H1& __h1, const _H2& __h2, const _Hash& __h,

		 const _Equal& __eq, const _ExtractKey& __exk,

		 const allocator_type& __a)

	: _Hashtable(__h1, __h2, __h, __eq, __exk, __a)

      {

	auto __nb_elems = __detail::__distance_fw(__f, __l);

	auto __bkt_count =

	  _M_rehash_policy._M_next_bkt(

	    std::max(_M_rehash_policy._M_bkt_for_elements(__nb_elems),

		     __bucket_hint));

	if (__bkt_count > _M_bucket_count)

	  {

	    _M_buckets = _M_allocate_buckets(__bkt_count);

	    _M_bucket_count = __bkt_count;

	  }

	__try

	  {

	    for (; __f != __l; ++__f)

	      this->insert(*__f);

	  }

	__catch(...)

	  {

	    clear();

	    _M_deallocate_buckets();

	    __throw_exception_again;

	  }

      }

  template

	   typename _Alloc, typename _ExtractKey, typename _Equal,

	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,

	   typename _Traits>

    auto

    _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,

	       _H1, _H2, _Hash, _RehashPolicy, _Traits>::

    operator=(const _Hashtable& __ht)

    -> _Hashtable&

    {

      if (&__ht == this)

	return *this;

      if (__node_alloc_traits::_S_propagate_on_copy_assign())

	{

	  auto& __this_alloc = this->_M_node_allocator();

	  auto& __that_alloc = __ht._M_node_allocator();

	  if (!__node_alloc_traits::_S_always_equal()

	      && __this_alloc != __that_alloc)

	    {

	      // Replacement allocator cannot free existing storage.

	      this->_M_deallocate_nodes(_M_begin());

	      _M_before_begin._M_nxt = nullptr;

	      _M_deallocate_buckets();

	      _M_buckets = nullptr;

	      std::__alloc_on_copy(__this_alloc, __that_alloc);

	      __hashtable_base::operator=(__ht);

	      _M_bucket_count = __ht._M_bucket_count;

	      _M_element_count = __ht._M_element_count;

	      _M_rehash_policy = __ht._M_rehash_policy;

	      __try

		{

		  _M_assign(__ht,

			    [this](const __node_type* __n)

			    { return this->_M_allocate_node(__n->_M_v()); });

		}

	      __catch(...)

		{

		  // _M_assign took care of deallocating all memory. Now we

		  // must make sure this instance remains in a usable state.

		  _M_reset();

		  __throw_exception_again;

		}

	      return *this;

	    }

	  std::__alloc_on_copy(__this_alloc, __that_alloc);

	}

      // Reuse allocated buckets and nodes.

      __bucket_type* __former_buckets = nullptr;

      std::size_t __former_bucket_count = _M_bucket_count;

      const __rehash_state& __former_state = _M_rehash_policy._M_state();

      if (_M_bucket_count != __ht._M_bucket_count)

	{

	  __former_buckets = _M_buckets;

	  _M_buckets = _M_allocate_buckets(__ht._M_bucket_count);

	  _M_bucket_count = __ht._M_bucket_count;

	}

      else

	__builtin_memset(_M_buckets, 0,

			 _M_bucket_count * sizeof(__bucket_type));

      __try

	{

	  __hashtable_base::operator=(__ht);

	  _M_element_count = __ht._M_element_count;

	  _M_rehash_policy = __ht._M_rehash_policy;

	  __reuse_or_alloc_node_type __roan(_M_begin(), *this);

	  _M_before_begin._M_nxt = nullptr;

	  _M_assign(__ht,

		    [&__roan](const __node_type* __n)

		    { return __roan(__n->_M_v()); });

	  if (__former_buckets)

	    _M_deallocate_buckets(__former_buckets, __former_bucket_count);

	}

      __catch(...)

	{

	  if (__former_buckets)

	    {

	      // Restore previous buckets.

	      _M_deallocate_buckets();

	      _M_rehash_policy._M_reset(__former_state);

	      _M_buckets = __former_buckets;

	      _M_bucket_count = __former_bucket_count;

	    }

	  __builtin_memset(_M_buckets, 0,

			   _M_bucket_count * sizeof(__bucket_type));

	  __throw_exception_again;

	}

      return *this;

    }

  template

	   typename _Alloc, typename _ExtractKey, typename _Equal,

	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,

	   typename _Traits>

    template

      void

      _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,

		 _H1, _H2, _Hash, _RehashPolicy, _Traits>::

      _M_assign(const _Hashtable& __ht, const _NodeGenerator& __node_gen)

      {

	__bucket_type* __buckets = nullptr;

	if (!_M_buckets)

	  _M_buckets = __buckets = _M_allocate_buckets(_M_bucket_count);

	__try

	  {

	    if (!__ht._M_before_begin._M_nxt)

	      return;

	    // First deal with the special first node pointed to by

	    // _M_before_begin.

	    __node_type* __ht_n = __ht._M_begin();

	    __node_type* __this_n = __node_gen(__ht_n);

	    this->_M_copy_code(__this_n, __ht_n);

	    _M_before_begin._M_nxt = __this_n;

	    _M_buckets[_M_bucket_index(__this_n)] = &_M_before_begin;

	    // Then deal with other nodes.

	    __node_base* __prev_n = __this_n;

	    for (__ht_n = __ht_n->_M_next(); __ht_n; __ht_n = __ht_n->_M_next())

	      {

		__this_n = __node_gen(__ht_n);

		__prev_n->_M_nxt = __this_n;

		this->_M_copy_code(__this_n, __ht_n);

		size_type __bkt = _M_bucket_index(__this_n);

		if (!_M_buckets[__bkt])

		  _M_buckets[__bkt] = __prev_n;

		__prev_n = __this_n;

	      }

	  }

	__catch(...)

	  {

	    clear();

	    if (__buckets)

	      _M_deallocate_buckets();

	    __throw_exception_again;

	  }

      }

  template

	   typename _Alloc, typename _ExtractKey, typename _Equal,

	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,

	   typename _Traits>

    void

    _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,

	       _H1, _H2, _Hash, _RehashPolicy, _Traits>::

    _M_reset() noexcept

    {

      _M_rehash_policy._M_reset();

      _M_bucket_count = 1;

      _M_single_bucket = nullptr;

      _M_buckets = &_M_single_bucket;

      _M_before_begin._M_nxt = nullptr;

      _M_element_count = 0;

    }

  template

	   typename _Alloc, typename _ExtractKey, typename _Equal,

	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,

	   typename _Traits>

    void

    _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,

	       _H1, _H2, _Hash, _RehashPolicy, _Traits>::

    _M_move_assign(_Hashtable&& __ht, std::true_type)

    {

      this->_M_deallocate_nodes(_M_begin());

      _M_deallocate_buckets();

      __hashtable_base::operator=(std::move(__ht));

      _M_rehash_policy = __ht._M_rehash_policy;

      if (!__ht._M_uses_single_bucket())

	_M_buckets = __ht._M_buckets;

      else

	{

	  _M_buckets = &_M_single_bucket;

	  _M_single_bucket = __ht._M_single_bucket;

	}

      _M_bucket_count = __ht._M_bucket_count;

      _M_before_begin._M_nxt = __ht._M_before_begin._M_nxt;

      _M_element_count = __ht._M_element_count;

      std::__alloc_on_move(this->_M_node_allocator(), __ht._M_node_allocator());

      // Fix buckets containing the _M_before_begin pointers that can't be

      // moved.

      if (_M_begin())

	_M_buckets[_M_bucket_index(_M_begin())] = &_M_before_begin;

      __ht._M_reset();

    }

  template

	   typename _Alloc, typename _ExtractKey, typename _Equal,

	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,

	   typename _Traits>

    void

    _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,

	       _H1, _H2, _Hash, _RehashPolicy, _Traits>::

    _M_move_assign(_Hashtable&& __ht, std::false_type)

    {

      if (__ht._M_node_allocator() == this->_M_node_allocator())

	_M_move_assign(std::move(__ht), std::true_type());

      else

	{

	  // Can't move memory, move elements then.

	  __bucket_type* __former_buckets = nullptr;

	  size_type __former_bucket_count = _M_bucket_count;

	  const __rehash_state& __former_state = _M_rehash_policy._M_state();

	  if (_M_bucket_count != __ht._M_bucket_count)

	    {

	      __former_buckets = _M_buckets;

	      _M_buckets = _M_allocate_buckets(__ht._M_bucket_count);

	      _M_bucket_count = __ht._M_bucket_count;

	    }

	  else

	    __builtin_memset(_M_buckets, 0,

			     _M_bucket_count * sizeof(__bucket_type));

	  __try

	    {

	      __hashtable_base::operator=(std::move(__ht));

	      _M_element_count = __ht._M_element_count;

	      _M_rehash_policy = __ht._M_rehash_policy;

	      __reuse_or_alloc_node_type __roan(_M_begin(), *this);

	      _M_before_begin._M_nxt = nullptr;

	      _M_assign(__ht,

			[&__roan](__node_type* __n)

			{ return __roan(std::move_if_noexcept(__n->_M_v())); });

	      __ht.clear();

	    }

	  __catch(...)

	    {

	      if (__former_buckets)

		{

		  _M_deallocate_buckets();

		  _M_rehash_policy._M_reset(__former_state);

		  _M_buckets = __former_buckets;

		  _M_bucket_count = __former_bucket_count;

		}

	      __builtin_memset(_M_buckets, 0,

			       _M_bucket_count * sizeof(__bucket_type));

	      __throw_exception_again;

	    }

	}

    }

  template

	   typename _Alloc, typename _ExtractKey, typename _Equal,

	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,

	   typename _Traits>

    _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,

	       _H1, _H2, _Hash, _RehashPolicy, _Traits>::

    _Hashtable(const _Hashtable& __ht)

    : __hashtable_base(__ht),

      __map_base(__ht),

      __rehash_base(__ht),

      __hashtable_alloc(

	__node_alloc_traits::_S_select_on_copy(__ht._M_node_allocator())),

      _M_buckets(nullptr),

      _M_bucket_count(__ht._M_bucket_count),

      _M_element_count(__ht._M_element_count),

      _M_rehash_policy(__ht._M_rehash_policy)

    {

      _M_assign(__ht,

		[this](const __node_type* __n)

		{ return this->_M_allocate_node(__n->_M_v()); });

    }

  template

	   typename _Alloc, typename _ExtractKey, typename _Equal,

	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,

	   typename _Traits>

    _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,