--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libstdc++-v3/include/bits/hashtable.h	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,2216 @@
+// hashtable.h header -*- C++ -*-
+
+// Copyright (C) 2007-2017 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
+// <http://www.gnu.org/licenses/>.
+
+/** @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 <bits/hashtable_policy.h>
+#if __cplusplus > 201402L
+# include <bits/node_handle.h>
+#endif
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+  template<typename _Tp, typename _Hash>
+    using __cache_default
+      =  __not_<__and_<// Do not cache for fast hasher.
+		       __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<size_t>:::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, <anything>)
+   *
+   *  @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<std::forward_list<_Node>::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 _Key, typename _Value, typename _Alloc,
+	   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<
+	__alloc_rebind<_Alloc,
+		       __detail::_Hash_node<_Value,
+					    _Traits::__hash_cached::value>>>
+    {
+      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 = __alloc_rebind<_Alloc, __node_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<typename _Cond>
+	using __if_hash_cached = __or_<__not_<__hash_cached>, _Cond>;
+
+      template<typename _Cond>
+	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<const __hash_code_base_access&>()
+			     ._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<is_default_constructible<_H2>>::value,
+		    "Functor used to map hash code to bucket index"
+		    " must be default constructible");
+
+      template<typename _Keya, typename _Valuea, typename _Alloca,
+	       typename _ExtractKeya, typename _Equala,
+	       typename _H1a, typename _H2a, typename _Hasha,
+	       typename _RehashPolicya, typename _Traitsa,
+	       bool _Unique_keysa>
+	friend struct __detail::_Map_base;
+
+      template<typename _Keya, typename _Valuea, typename _Alloca,
+	       typename _ExtractKeya, typename _Equala,
+	       typename _H1a, typename _H2a, typename _Hasha,
+	       typename _RehashPolicya, typename _Traitsa>
+	friend struct __detail::_Insert_base;
+
+      template<typename _Keya, typename _Valuea, typename _Alloca,
+	       typename _ExtractKeya, typename _Equala,
+	       typename _H1a, typename _H2a, typename _Hasha,
+	       typename _RehashPolicya, typename _Traitsa,
+	       bool _Constant_iteratorsa>
+	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;
+
+#if __cplusplus > 201402L
+      using node_type = _Node_handle<_Key, _Value, __node_alloc_type>;
+      using insert_return_type = _Node_insert_return<iterator, node_type>;
+#endif
+
+    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<typename _NodeGenerator>
+	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<typename _InputIterator>
+	_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<typename _InputIterator>
+	_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<value_type> __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()
+	       && is_nothrow_move_assignable<_H1>::value
+	       && is_nothrow_move_assignable<_Equal>::value)
+      {
+        constexpr bool __move_storage =
+	  __node_alloc_traits::_S_propagate_on_move_assign()
+	  || __node_alloc_traits::_S_always_equal();
+	_M_move_assign(std::move(__ht), __bool_constant<__move_storage>());
+	return *this;
+      }
+
+      _Hashtable&
+      operator=(initializer_list<value_type> __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(__and_<__is_nothrow_swappable<_H1>,
+	                  __is_nothrow_swappable<_Equal>>::value);
+
+      // 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<float>(size()) / static_cast<float>(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& __pol)
+      { _M_rehash_policy = __pol; }
+
+      // 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<iterator, iterator>
+      equal_range(const key_type& __k);
+
+      std::pair<const_iterator, const_iterator>
+      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<typename... _Args>
+	std::pair<iterator, bool>
+	_M_emplace(std::true_type, _Args&&... __args);
+
+      template<typename... _Args>
+	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<typename... _Args>
+	iterator
+	_M_emplace(const_iterator, std::true_type __uk, _Args&&... __args)
+	{ return _M_emplace(__uk, std::forward<_Args>(__args)...).first; }
+
+      template<typename... _Args>
+	iterator
+	_M_emplace(const_iterator, std::false_type, _Args&&... __args);
+
+      template<typename _Arg, typename _NodeGenerator>
+	std::pair<iterator, bool>
+	_M_insert(_Arg&&, const _NodeGenerator&, std::true_type);
+
+      template<typename _Arg, typename _NodeGenerator>
+	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<typename _Arg, typename _NodeGenerator>
+	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<typename _Arg, typename _NodeGenerator>
+	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<typename... _Args>
+	__ireturn_type
+	emplace(_Args&&... __args)
+	{ return _M_emplace(__unique_keys(), std::forward<_Args>(__args)...); }
+
+      template<typename... _Args>
+	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.
+
+#if __cplusplus > 201402L
+      /// Re-insert an extracted node into a container with unique keys.
+      insert_return_type
+      _M_reinsert_node(node_type&& __nh)
+      {
+	insert_return_type __ret;
+	if (__nh.empty())
+	  __ret.position = end();
+	else
+	  {
+	    __glibcxx_assert(get_allocator() == __nh.get_allocator());
+
+	    const key_type& __k = __nh._M_key();
+	    __hash_code __code = this->_M_hash_code(__k);
+	    size_type __bkt = _M_bucket_index(__k, __code);
+	    if (__node_type* __n = _M_find_node(__bkt, __k, __code))
+	      {
+		__ret.node = std::move(__nh);
+		__ret.position = iterator(__n);
+		__ret.inserted = false;
+	      }
+	    else
+	      {
+		__ret.position
+		  = _M_insert_unique_node(__bkt, __code, __nh._M_ptr);
+		__nh._M_ptr = nullptr;
+		__ret.inserted = true;
+	      }
+	  }
+	return __ret;
+      }
+
+      /// Re-insert an extracted node into a container with equivalent keys.
+      iterator
+      _M_reinsert_node_multi(const_iterator __hint, node_type&& __nh)
+      {
+	iterator __ret;
+	if (__nh.empty())
+	  __ret = end();
+	else
+	  {
+	    __glibcxx_assert(get_allocator() == __nh.get_allocator());
+
+	    auto __code = this->_M_hash_code(__nh._M_key());
+	    auto __node = std::exchange(__nh._M_ptr, nullptr);
+	    // FIXME: this deallocates the node on exception.
+	    __ret = _M_insert_multi_node(__hint._M_cur, __code, __node);
+	  }
+	return __ret;
+      }
+
+      /// Extract a node.
+      node_type
+      extract(const_iterator __pos)
+      {
+	__node_type* __n = __pos._M_cur;
+	size_t __bkt = _M_bucket_index(__n);
+
+	// Look for previous node to unlink it from the erased one, this
+	// is why we need buckets to contain the before begin to make
+	// this search fast.
+	__node_base* __prev_n = _M_get_previous_node(__bkt, __n);
+
+	if (__prev_n == _M_buckets[__bkt])
+	  _M_remove_bucket_begin(__bkt, __n->_M_next(),
+	     __n->_M_nxt ? _M_bucket_index(__n->_M_next()) : 0);
+	else if (__n->_M_nxt)
+	  {
+	    size_type __next_bkt = _M_bucket_index(__n->_M_next());
+	    if (__next_bkt != __bkt)
+	      _M_buckets[__next_bkt] = __prev_n;
+	  }
+
+	__prev_n->_M_nxt = __n->_M_nxt;
+	__n->_M_nxt = nullptr;
+	--_M_element_count;
+	return { __n, this->_M_node_allocator() };
+      }
+
+      /// Extract a node.
+      node_type
+      extract(const _Key& __k)
+      {
+	node_type __nh;
+	auto __pos = find(__k);
+	if (__pos != end())
+	  __nh = extract(const_iterator(__pos));
+	return __nh;
+      }
+
+      /// Merge from a compatible container into one with unique keys.
+      template<typename _Compatible_Hashtable>
+	void
+	_M_merge_unique(_Compatible_Hashtable& __src) noexcept
+	{
+	  static_assert(is_same_v<typename _Compatible_Hashtable::node_type,
+	      node_type>, "Node types are compatible");
+	  __glibcxx_assert(get_allocator() == __src.get_allocator());
+
+	  for (auto __i = __src.begin(), __end = __src.end(); __i != __end;)
+	    {
+	      auto __pos = __i++;
+	      const key_type& __k = this->_M_extract()(__pos._M_cur->_M_v());
+	      __hash_code __code = this->_M_hash_code(__k);
+	      size_type __bkt = _M_bucket_index(__k, __code);
+	      if (_M_find_node(__bkt, __k, __code) == nullptr)
+		{
+		  auto __nh = __src.extract(__pos);
+		  _M_insert_unique_node(__bkt, __code, __nh._M_ptr);
+		  __nh._M_ptr = nullptr;
+		}
+	    }
+	}
+
+      /// Merge from a compatible container into one with equivalent keys.
+      template<typename _Compatible_Hashtable>
+	void
+	_M_merge_multi(_Compatible_Hashtable& __src) noexcept
+	{
+	  static_assert(is_same_v<typename _Compatible_Hashtable::node_type,
+	      node_type>, "Node types are compatible");
+	  __glibcxx_assert(get_allocator() == __src.get_allocator());
+
+	  this->reserve(size() + __src.size());
+	  for (auto __i = __src.begin(), __end = __src.end(); __i != __end;)
+	    _M_reinsert_node_multi(cend(), __src.extract(__i++));
+	}
+#endif // C++17
+
+    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 _Key, typename _Value,
+	   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 _Key, typename _Value,
+	   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 _Key, typename _Value,
+	   typename _Alloc, typename _ExtractKey, typename _Equal,
+	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,
+	   typename _Traits>
+    template<typename _InputIterator>
+      _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;
+	  }
+
+	for (; __f != __l; ++__f)
+	  this->insert(*__f);
+      }
+
+  template<typename _Key, typename _Value,
+	   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 _Key, typename _Value,
+	   typename _Alloc, typename _ExtractKey, typename _Equal,
+	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,
+	   typename _Traits>
+    template<typename _NodeGenerator>
+      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 _Key, typename _Value,
+	   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 _Key, typename _Value,
+	   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 _Key, typename _Value,
+	   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 _Key, typename _Value,
+	   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 _Key, typename _Value,
+	   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(_Hashtable&& __ht) noexcept
+    : __hashtable_base(__ht),
+      __map_base(__ht),
+      __rehash_base(__ht),
+      __hashtable_alloc(std::move(__ht._M_base_alloc())),
+      _M_buckets(__ht._M_buckets),
+      _M_bucket_count(__ht._M_bucket_count),
+      _M_before_begin(__ht._M_before_begin._M_nxt),
+      _M_element_count(__ht._M_element_count),
+      _M_rehash_policy(__ht._M_rehash_policy)
+    {
+      // Update, if necessary, buckets if __ht is using its single bucket.
+      if (__ht._M_uses_single_bucket())
+	{
+	  _M_buckets = &_M_single_bucket;
+	  _M_single_bucket = __ht._M_single_bucket;
+	}
+
+      // Update, if necessary, bucket pointing to before begin that hasn't
+      // moved.
+      if (_M_begin())
+	_M_buckets[_M_bucket_index(_M_begin())] = &_M_before_begin;
+
+      __ht._M_reset();
+    }
+
+  template<typename _Key, typename _Value,
+	   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, const allocator_type& __a)
+    : __hashtable_base(__ht),
+      __map_base(__ht),
+      __rehash_base(__ht),
+      __hashtable_alloc(__node_alloc_type(__a)),
+      _M_buckets(),
+      _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 _Key, typename _Value,
+	   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(_Hashtable&& __ht, const allocator_type& __a)
+    : __hashtable_base(__ht),
+      __map_base(__ht),
+      __rehash_base(__ht),
+      __hashtable_alloc(__node_alloc_type(__a)),
+      _M_buckets(nullptr),
+      _M_bucket_count(__ht._M_bucket_count),
+      _M_element_count(__ht._M_element_count),
+      _M_rehash_policy(__ht._M_rehash_policy)
+    {
+      if (__ht._M_node_allocator() == this->_M_node_allocator())
+	{
+	  if (__ht._M_uses_single_bucket())
+	    {
+	      _M_buckets = &_M_single_bucket;
+	      _M_single_bucket = __ht._M_single_bucket;
+	    }
+	  else
+	    _M_buckets = __ht._M_buckets;
+
+	  _M_before_begin._M_nxt = __ht._M_before_begin._M_nxt;
+	  // Update, if necessary, bucket pointing to before begin that hasn't
+	  // moved.
+	  if (_M_begin())
+	    _M_buckets[_M_bucket_index(_M_begin())] = &_M_before_begin;
+	  __ht._M_reset();
+	}
+      else
+	{
+	  _M_assign(__ht,
+		    [this](__node_type* __n)
+		    {
+		      return this->_M_allocate_node(
+					std::move_if_noexcept(__n->_M_v()));
+		    });
+	  __ht.clear();
+	}
+    }
+
+  template<typename _Key, typename _Value,
+	   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() noexcept
+    {
+      clear();
+      _M_deallocate_buckets();
+    }
+
+  template<typename _Key, typename _Value,
+	   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>::
+    swap(_Hashtable& __x)
+    noexcept(__and_<__is_nothrow_swappable<_H1>,
+	                __is_nothrow_swappable<_Equal>>::value)
+    {
+      // The only base class with member variables is hash_code_base.
+      // We define _Hash_code_base::_M_swap because different
+      // specializations have different members.
+      this->_M_swap(__x);
+
+      std::__alloc_on_swap(this->_M_node_allocator(), __x._M_node_allocator());
+      std::swap(_M_rehash_policy, __x._M_rehash_policy);
+
+      // Deal properly with potentially moved instances.
+      if (this->_M_uses_single_bucket())
+	{
+	  if (!__x._M_uses_single_bucket())
+	    {
+	      _M_buckets = __x._M_buckets;
+	      __x._M_buckets = &__x._M_single_bucket;
+	    }
+	}
+      else if (__x._M_uses_single_bucket())
+	{
+	  __x._M_buckets = _M_buckets;
+	  _M_buckets = &_M_single_bucket;
+	}	
+      else
+	std::swap(_M_buckets, __x._M_buckets);
+
+      std::swap(_M_bucket_count, __x._M_bucket_count);
+      std::swap(_M_before_begin._M_nxt, __x._M_before_begin._M_nxt);
+      std::swap(_M_element_count, __x._M_element_count);
+      std::swap(_M_single_bucket, __x._M_single_bucket);
+
+      // Fix buckets containing the _M_before_begin pointers that can't be
+      // swapped.
+      if (_M_begin())
+	_M_buckets[_M_bucket_index(_M_begin())] = &_M_before_begin;
+
+      if (__x._M_begin())
+	__x._M_buckets[__x._M_bucket_index(__x._M_begin())]
+	  = &__x._M_before_begin;
+    }
+
+  template<typename _Key, typename _Value,
+	   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>::
+    find(const key_type& __k)
+    -> iterator
+    {
+      __hash_code __code = this->_M_hash_code(__k);
+      std::size_t __n = _M_bucket_index(__k, __code);
+      __node_type* __p = _M_find_node(__n, __k, __code);
+      return __p ? iterator(__p) : end();
+    }
+
+  template<typename _Key, typename _Value,
+	   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>::
+    find(const key_type& __k) const
+    -> const_iterator
+    {
+      __hash_code __code = this->_M_hash_code(__k);
+      std::size_t __n = _M_bucket_index(__k, __code);
+      __node_type* __p = _M_find_node(__n, __k, __code);
+      return __p ? const_iterator(__p) : end();
+    }
+
+  template<typename _Key, typename _Value,
+	   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>::
+    count(const key_type& __k) const
+    -> size_type
+    {
+      __hash_code __code = this->_M_hash_code(__k);
+      std::size_t __n = _M_bucket_index(__k, __code);
+      __node_type* __p = _M_bucket_begin(__n);
+      if (!__p)
+	return 0;
+
+      std::size_t __result = 0;
+      for (;; __p = __p->_M_next())
+	{
+	  if (this->_M_equals(__k, __code, __p))
+	    ++__result;
+	  else if (__result)
+	    // All equivalent values are next to each other, if we
+	    // found a non-equivalent value after an equivalent one it
+	    // means that we won't find any new equivalent value.
+	    break;
+	  if (!__p->_M_nxt || _M_bucket_index(__p->_M_next()) != __n)
+	    break;
+	}
+      return __result;
+    }
+
+  template<typename _Key, typename _Value,
+	   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>::
+    equal_range(const key_type& __k)
+    -> pair<iterator, iterator>
+    {
+      __hash_code __code = this->_M_hash_code(__k);
+      std::size_t __n = _M_bucket_index(__k, __code);
+      __node_type* __p = _M_find_node(__n, __k, __code);
+
+      if (__p)
+	{
+	  __node_type* __p1 = __p->_M_next();
+	  while (__p1 && _M_bucket_index(__p1) == __n
+		 && this->_M_equals(__k, __code, __p1))
+	    __p1 = __p1->_M_next();
+
+	  return std::make_pair(iterator(__p), iterator(__p1));
+	}
+      else
+	return std::make_pair(end(), end());
+    }
+
+  template<typename _Key, typename _Value,
+	   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>::
+    equal_range(const key_type& __k) const
+    -> pair<const_iterator, const_iterator>
+    {
+      __hash_code __code = this->_M_hash_code(__k);
+      std::size_t __n = _M_bucket_index(__k, __code);
+      __node_type* __p = _M_find_node(__n, __k, __code);
+
+      if (__p)
+	{
+	  __node_type* __p1 = __p->_M_next();
+	  while (__p1 && _M_bucket_index(__p1) == __n
+		 && this->_M_equals(__k, __code, __p1))
+	    __p1 = __p1->_M_next();
+
+	  return std::make_pair(const_iterator(__p), const_iterator(__p1));
+	}
+      else
+	return std::make_pair(end(), end());
+    }
+
+  // Find the node whose key compares equal to k in the bucket n.
+  // Return nullptr if no node is found.
+  template<typename _Key, typename _Value,
+	   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_find_before_node(size_type __n, const key_type& __k,
+			__hash_code __code) const
+    -> __node_base*
+    {
+      __node_base* __prev_p = _M_buckets[__n];
+      if (!__prev_p)
+	return nullptr;
+
+      for (__node_type* __p = static_cast<__node_type*>(__prev_p->_M_nxt);;
+	   __p = __p->_M_next())
+	{
+	  if (this->_M_equals(__k, __code, __p))
+	    return __prev_p;
+
+	  if (!__p->_M_nxt || _M_bucket_index(__p->_M_next()) != __n)
+	    break;
+	  __prev_p = __p;
+	}
+      return nullptr;
+    }
+
+  template<typename _Key, typename _Value,
+	   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_insert_bucket_begin(size_type __bkt, __node_type* __node)
+    {
+      if (_M_buckets[__bkt])
+	{
+	  // Bucket is not empty, we just need to insert the new node
+	  // after the bucket before begin.
+	  __node->_M_nxt = _M_buckets[__bkt]->_M_nxt;
+	  _M_buckets[__bkt]->_M_nxt = __node;
+	}
+      else
+	{
+	  // The bucket is empty, the new node is inserted at the
+	  // beginning of the singly-linked list and the bucket will
+	  // contain _M_before_begin pointer.
+	  __node->_M_nxt = _M_before_begin._M_nxt;
+	  _M_before_begin._M_nxt = __node;
+	  if (__node->_M_nxt)
+	    // We must update former begin bucket that is pointing to
+	    // _M_before_begin.
+	    _M_buckets[_M_bucket_index(__node->_M_next())] = __node;
+	  _M_buckets[__bkt] = &_M_before_begin;
+	}
+    }
+
+  template<typename _Key, typename _Value,
+	   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_remove_bucket_begin(size_type __bkt, __node_type* __next,
+			   size_type __next_bkt)
+    {
+      if (!__next || __next_bkt != __bkt)
+	{
+	  // Bucket is now empty
+	  // First update next bucket if any
+	  if (__next)
+	    _M_buckets[__next_bkt] = _M_buckets[__bkt];
+
+	  // Second update before begin node if necessary
+	  if (&_M_before_begin == _M_buckets[__bkt])
+	    _M_before_begin._M_nxt = __next;
+	  _M_buckets[__bkt] = nullptr;
+	}
+    }
+
+  template<typename _Key, typename _Value,
+	   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_get_previous_node(size_type __bkt, __node_base* __n)
+    -> __node_base*
+    {
+      __node_base* __prev_n = _M_buckets[__bkt];
+      while (__prev_n->_M_nxt != __n)
+	__prev_n = __prev_n->_M_nxt;
+      return __prev_n;
+    }
+
+  template<typename _Key, typename _Value,
+	   typename _Alloc, typename _ExtractKey, typename _Equal,
+	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,
+	   typename _Traits>
+    template<typename... _Args>
+      auto
+      _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
+		 _H1, _H2, _Hash, _RehashPolicy, _Traits>::
+      _M_emplace(std::true_type, _Args&&... __args)
+      -> pair<iterator, bool>
+      {
+	// First build the node to get access to the hash code
+	__node_type* __node = this->_M_allocate_node(std::forward<_Args>(__args)...);
+	const key_type& __k = this->_M_extract()(__node->_M_v());
+	__hash_code __code;
+	__try
+	  {
+	    __code = this->_M_hash_code(__k);
+	  }
+	__catch(...)
+	  {
+	    this->_M_deallocate_node(__node);
+	    __throw_exception_again;
+	  }
+
+	size_type __bkt = _M_bucket_index(__k, __code);
+	if (__node_type* __p = _M_find_node(__bkt, __k, __code))
+	  {
+	    // There is already an equivalent node, no insertion
+	    this->_M_deallocate_node(__node);
+	    return std::make_pair(iterator(__p), false);
+	  }
+
+	// Insert the node
+	return std::make_pair(_M_insert_unique_node(__bkt, __code, __node),
+			      true);
+      }
+
+  template<typename _Key, typename _Value,
+	   typename _Alloc, typename _ExtractKey, typename _Equal,
+	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,
+	   typename _Traits>
+    template<typename... _Args>
+      auto
+      _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
+		 _H1, _H2, _Hash, _RehashPolicy, _Traits>::
+      _M_emplace(const_iterator __hint, std::false_type, _Args&&... __args)
+      -> iterator
+      {
+	// First build the node to get its hash code.
+	__node_type* __node =
+	  this->_M_allocate_node(std::forward<_Args>(__args)...);
+
+	__hash_code __code;
+	__try
+	  {
+	    __code = this->_M_hash_code(this->_M_extract()(__node->_M_v()));
+	  }
+	__catch(...)
+	  {
+	    this->_M_deallocate_node(__node);
+	    __throw_exception_again;
+	  }
+
+	return _M_insert_multi_node(__hint._M_cur, __code, __node);
+      }
+
+  template<typename _Key, typename _Value,
+	   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_insert_unique_node(size_type __bkt, __hash_code __code,
+			  __node_type* __node)
+    -> iterator
+    {
+      const __rehash_state& __saved_state = _M_rehash_policy._M_state();
+      std::pair<bool, std::size_t> __do_rehash
+	= _M_rehash_policy._M_need_rehash(_M_bucket_count, _M_element_count, 1);
+
+      __try
+	{
+	  if (__do_rehash.first)
+	    {
+	      _M_rehash(__do_rehash.second, __saved_state);
+	      __bkt = _M_bucket_index(this->_M_extract()(__node->_M_v()), __code);
+	    }
+
+	  this->_M_store_code(__node, __code);
+
+	  // Always insert at the beginning of the bucket.
+	  _M_insert_bucket_begin(__bkt, __node);
+	  ++_M_element_count;
+	  return iterator(__node);
+	}
+      __catch(...)
+	{
+	  this->_M_deallocate_node(__node);
+	  __throw_exception_again;
+	}
+    }
+
+  // Insert node, in bucket bkt if no rehash (assumes no element with its key
+  // already present). Take ownership of the node, deallocate it on exception.
+  template<typename _Key, typename _Value,
+	   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_insert_multi_node(__node_type* __hint, __hash_code __code,
+			 __node_type* __node)
+    -> iterator
+    {
+      const __rehash_state& __saved_state = _M_rehash_policy._M_state();
+      std::pair<bool, std::size_t> __do_rehash
+	= _M_rehash_policy._M_need_rehash(_M_bucket_count, _M_element_count, 1);
+
+      __try
+	{
+	  if (__do_rehash.first)
+	    _M_rehash(__do_rehash.second, __saved_state);
+
+	  this->_M_store_code(__node, __code);
+	  const key_type& __k = this->_M_extract()(__node->_M_v());
+	  size_type __bkt = _M_bucket_index(__k, __code);
+
+	  // Find the node before an equivalent one or use hint if it exists and
+	  // if it is equivalent.
+	  __node_base* __prev
+	    = __builtin_expect(__hint != nullptr, false)
+	      && this->_M_equals(__k, __code, __hint)
+		? __hint
+		: _M_find_before_node(__bkt, __k, __code);
+	  if (__prev)
+	    {
+	      // Insert after the node before the equivalent one.
+	      __node->_M_nxt = __prev->_M_nxt;
+	      __prev->_M_nxt = __node;
+	      if (__builtin_expect(__prev == __hint, false))
+	      	// hint might be the last bucket node, in this case we need to
+	      	// update next bucket.
+	      	if (__node->_M_nxt
+	      	    && !this->_M_equals(__k, __code, __node->_M_next()))
+	      	  {
+	      	    size_type __next_bkt = _M_bucket_index(__node->_M_next());
+	      	    if (__next_bkt != __bkt)
+	      	      _M_buckets[__next_bkt] = __node;
+	      	  }
+	    }
+	  else
+	    // The inserted node has no equivalent in the
+	    // hashtable. We must insert the new node at the
+	    // beginning of the bucket to preserve equivalent
+	    // elements' relative positions.
+	    _M_insert_bucket_begin(__bkt, __node);
+	  ++_M_element_count;
+	  return iterator(__node);
+	}
+      __catch(...)
+	{
+	  this->_M_deallocate_node(__node);
+	  __throw_exception_again;
+	}
+    }
+
+  // Insert v if no element with its key is already present.
+  template<typename _Key, typename _Value,
+	   typename _Alloc, typename _ExtractKey, typename _Equal,
+	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,
+	   typename _Traits>
+    template<typename _Arg, typename _NodeGenerator>
+      auto
+      _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
+		 _H1, _H2, _Hash, _RehashPolicy, _Traits>::
+      _M_insert(_Arg&& __v, const _NodeGenerator& __node_gen, std::true_type)
+      -> pair<iterator, bool>
+      {
+	const key_type& __k = this->_M_extract()(__v);
+	__hash_code __code = this->_M_hash_code(__k);
+	size_type __bkt = _M_bucket_index(__k, __code);
+
+	__node_type* __n = _M_find_node(__bkt, __k, __code);
+	if (__n)
+	  return std::make_pair(iterator(__n), false);
+
+	__n = __node_gen(std::forward<_Arg>(__v));
+	return std::make_pair(_M_insert_unique_node(__bkt, __code, __n), true);
+      }
+
+  // Insert v unconditionally.
+  template<typename _Key, typename _Value,
+	   typename _Alloc, typename _ExtractKey, typename _Equal,
+	   typename _H1, typename _H2, typename _Hash, typename _RehashPolicy,
+	   typename _Traits>
+    template<typename _Arg, typename _NodeGenerator>
+      auto
+      _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
+		 _H1, _H2, _Hash, _RehashPolicy, _Traits>::
+      _M_insert(const_iterator __hint, _Arg&& __v,
+		const _NodeGenerator& __node_gen, std::false_type)
+      -> iterator
+      {
+	// First compute the hash code so that we don't do anything if it
+	// throws.
+	__hash_code __code = this->_M_hash_code(this->_M_extract()(__v));
+
+	// Second allocate new node so that we don't rehash if it throws.
+	__node_type* __node = __node_gen(std::forward<_Arg>(__v));
+
+	return _M_insert_multi_node(__hint._M_cur, __code, __node);
+      }
+
+  template<typename _Key, typename _Value,
+	   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>::
+    erase(const_iterator __it)
+    -> iterator
+    {
+      __node_type* __n = __it._M_cur;
+      std::size_t __bkt = _M_bucket_index(__n);
+
+      // Look for previous node to unlink it from the erased one, this
+      // is why we need buckets to contain the before begin to make
+      // this search fast.
+      __node_base* __prev_n = _M_get_previous_node(__bkt, __n);
+      return _M_erase(__bkt, __prev_n, __n);
+    }
+
+  template<typename _Key, typename _Value,
+	   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_erase(size_type __bkt, __node_base* __prev_n, __node_type* __n)
+    -> iterator
+    {
+      if (__prev_n == _M_buckets[__bkt])
+	_M_remove_bucket_begin(__bkt, __n->_M_next(),
+	   __n->_M_nxt ? _M_bucket_index(__n->_M_next()) : 0);
+      else if (__n->_M_nxt)
+	{
+	  size_type __next_bkt = _M_bucket_index(__n->_M_next());
+	  if (__next_bkt != __bkt)
+	    _M_buckets[__next_bkt] = __prev_n;
+	}
+
+      __prev_n->_M_nxt = __n->_M_nxt;
+      iterator __result(__n->_M_next());
+      this->_M_deallocate_node(__n);
+      --_M_element_count;
+
+      return __result;
+    }
+
+  template<typename _Key, typename _Value,
+	   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_erase(std::true_type, const key_type& __k)
+    -> size_type
+    {
+      __hash_code __code = this->_M_hash_code(__k);
+      std::size_t __bkt = _M_bucket_index(__k, __code);
+
+      // Look for the node before the first matching node.
+      __node_base* __prev_n = _M_find_before_node(__bkt, __k, __code);
+      if (!__prev_n)
+	return 0;
+
+      // We found a matching node, erase it.
+      __node_type* __n = static_cast<__node_type*>(__prev_n->_M_nxt);
+      _M_erase(__bkt, __prev_n, __n);
+      return 1;
+    }
+
+  template<typename _Key, typename _Value,
+	   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_erase(std::false_type, const key_type& __k)
+    -> size_type
+    {
+      __hash_code __code = this->_M_hash_code(__k);
+      std::size_t __bkt = _M_bucket_index(__k, __code);
+
+      // Look for the node before the first matching node.
+      __node_base* __prev_n = _M_find_before_node(__bkt, __k, __code);
+      if (!__prev_n)
+	return 0;
+
+      // _GLIBCXX_RESOLVE_LIB_DEFECTS
+      // 526. Is it undefined if a function in the standard changes
+      // in parameters?
+      // We use one loop to find all matching nodes and another to deallocate
+      // them so that the key stays valid during the first loop. It might be
+      // invalidated indirectly when destroying nodes.
+      __node_type* __n = static_cast<__node_type*>(__prev_n->_M_nxt);
+      __node_type* __n_last = __n;
+      std::size_t __n_last_bkt = __bkt;
+      do
+	{
+	  __n_last = __n_last->_M_next();
+	  if (!__n_last)
+	    break;
+	  __n_last_bkt = _M_bucket_index(__n_last);
+	}
+      while (__n_last_bkt == __bkt && this->_M_equals(__k, __code, __n_last));
+
+      // Deallocate nodes.
+      size_type __result = 0;
+      do
+	{
+	  __node_type* __p = __n->_M_next();
+	  this->_M_deallocate_node(__n);
+	  __n = __p;
+	  ++__result;
+	  --_M_element_count;
+	}
+      while (__n != __n_last);
+
+      if (__prev_n == _M_buckets[__bkt])
+	_M_remove_bucket_begin(__bkt, __n_last, __n_last_bkt);
+      else if (__n_last && __n_last_bkt != __bkt)
+	_M_buckets[__n_last_bkt] = __prev_n;
+      __prev_n->_M_nxt = __n_last;
+      return __result;
+    }
+
+  template<typename _Key, typename _Value,
+	   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>::
+    erase(const_iterator __first, const_iterator __last)
+    -> iterator
+    {
+      __node_type* __n = __first._M_cur;
+      __node_type* __last_n = __last._M_cur;
+      if (__n == __last_n)
+	return iterator(__n);
+
+      std::size_t __bkt = _M_bucket_index(__n);
+
+      __node_base* __prev_n = _M_get_previous_node(__bkt, __n);
+      bool __is_bucket_begin = __n == _M_bucket_begin(__bkt);
+      std::size_t __n_bkt = __bkt;
+      for (;;)
+	{
+	  do
+	    {
+	      __node_type* __tmp = __n;
+	      __n = __n->_M_next();
+	      this->_M_deallocate_node(__tmp);
+	      --_M_element_count;
+	      if (!__n)
+		break;
+	      __n_bkt = _M_bucket_index(__n);
+	    }
+	  while (__n != __last_n && __n_bkt == __bkt);
+	  if (__is_bucket_begin)
+	    _M_remove_bucket_begin(__bkt, __n, __n_bkt);
+	  if (__n == __last_n)
+	    break;
+	  __is_bucket_begin = true;
+	  __bkt = __n_bkt;
+	}
+
+      if (__n && (__n_bkt != __bkt || __is_bucket_begin))
+	_M_buckets[__n_bkt] = __prev_n;
+      __prev_n->_M_nxt = __n;
+      return iterator(__n);
+    }
+
+  template<typename _Key, typename _Value,
+	   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>::
+    clear() noexcept
+    {
+      this->_M_deallocate_nodes(_M_begin());
+      __builtin_memset(_M_buckets, 0, _M_bucket_count * sizeof(__bucket_type));
+      _M_element_count = 0;
+      _M_before_begin._M_nxt = nullptr;
+    }
+
+  template<typename _Key, typename _Value,
+	   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>::
+    rehash(size_type __n)
+    {
+      const __rehash_state& __saved_state = _M_rehash_policy._M_state();
+      std::size_t __buckets
+	= std::max(_M_rehash_policy._M_bkt_for_elements(_M_element_count + 1),
+		   __n);
+      __buckets = _M_rehash_policy._M_next_bkt(__buckets);
+
+      if (__buckets != _M_bucket_count)
+	_M_rehash(__buckets, __saved_state);
+      else
+	// No rehash, restore previous state to keep a consistent state.
+	_M_rehash_policy._M_reset(__saved_state);
+    }
+
+  template<typename _Key, typename _Value,
+	   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_rehash(size_type __n, const __rehash_state& __state)
+    {
+      __try
+	{
+	  _M_rehash_aux(__n, __unique_keys());
+	}
+      __catch(...)
+	{
+	  // A failure here means that buckets allocation failed.  We only
+	  // have to restore hash policy previous state.
+	  _M_rehash_policy._M_reset(__state);
+	  __throw_exception_again;
+	}
+    }
+
+  // Rehash when there is no equivalent elements.
+  template<typename _Key, typename _Value,
+	   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_rehash_aux(size_type __n, std::true_type)
+    {
+      __bucket_type* __new_buckets = _M_allocate_buckets(__n);
+      __node_type* __p = _M_begin();
+      _M_before_begin._M_nxt = nullptr;
+      std::size_t __bbegin_bkt = 0;
+      while (__p)
+	{
+	  __node_type* __next = __p->_M_next();
+	  std::size_t __bkt = __hash_code_base::_M_bucket_index(__p, __n);
+	  if (!__new_buckets[__bkt])
+	    {
+	      __p->_M_nxt = _M_before_begin._M_nxt;
+	      _M_before_begin._M_nxt = __p;
+	      __new_buckets[__bkt] = &_M_before_begin;
+	      if (__p->_M_nxt)
+		__new_buckets[__bbegin_bkt] = __p;
+	      __bbegin_bkt = __bkt;
+	    }
+	  else
+	    {
+	      __p->_M_nxt = __new_buckets[__bkt]->_M_nxt;
+	      __new_buckets[__bkt]->_M_nxt = __p;
+	    }
+	  __p = __next;
+	}
+
+      _M_deallocate_buckets();
+      _M_bucket_count = __n;
+      _M_buckets = __new_buckets;
+    }
+
+  // Rehash when there can be equivalent elements, preserve their relative
+  // order.
+  template<typename _Key, typename _Value,
+	   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_rehash_aux(size_type __n, std::false_type)
+    {
+      __bucket_type* __new_buckets = _M_allocate_buckets(__n);
+
+      __node_type* __p = _M_begin();
+      _M_before_begin._M_nxt = nullptr;
+      std::size_t __bbegin_bkt = 0;
+      std::size_t __prev_bkt = 0;
+      __node_type* __prev_p = nullptr;
+      bool __check_bucket = false;
+
+      while (__p)
+	{
+	  __node_type* __next = __p->_M_next();
+	  std::size_t __bkt = __hash_code_base::_M_bucket_index(__p, __n);
+
+	  if (__prev_p && __prev_bkt == __bkt)
+	    {
+	      // Previous insert was already in this bucket, we insert after
+	      // the previously inserted one to preserve equivalent elements
+	      // relative order.
+	      __p->_M_nxt = __prev_p->_M_nxt;
+	      __prev_p->_M_nxt = __p;
+
+	      // Inserting after a node in a bucket require to check that we
+	      // haven't change the bucket last node, in this case next
+	      // bucket containing its before begin node must be updated. We
+	      // schedule a check as soon as we move out of the sequence of
+	      // equivalent nodes to limit the number of checks.
+	      __check_bucket = true;
+	    }
+	  else
+	    {
+	      if (__check_bucket)
+		{
+		  // Check if we shall update the next bucket because of
+		  // insertions into __prev_bkt bucket.
+		  if (__prev_p->_M_nxt)
+		    {
+		      std::size_t __next_bkt
+			= __hash_code_base::_M_bucket_index(__prev_p->_M_next(),
+							    __n);
+		      if (__next_bkt != __prev_bkt)
+			__new_buckets[__next_bkt] = __prev_p;
+		    }
+		  __check_bucket = false;
+		}
+
+	      if (!__new_buckets[__bkt])
+		{
+		  __p->_M_nxt = _M_before_begin._M_nxt;
+		  _M_before_begin._M_nxt = __p;
+		  __new_buckets[__bkt] = &_M_before_begin;
+		  if (__p->_M_nxt)
+		    __new_buckets[__bbegin_bkt] = __p;
+		  __bbegin_bkt = __bkt;
+		}
+	      else
+		{
+		  __p->_M_nxt = __new_buckets[__bkt]->_M_nxt;
+		  __new_buckets[__bkt]->_M_nxt = __p;
+		}
+	    }
+	  __prev_p = __p;
+	  __prev_bkt = __bkt;
+	  __p = __next;
+	}
+
+      if (__check_bucket && __prev_p->_M_nxt)
+	{
+	  std::size_t __next_bkt
+	    = __hash_code_base::_M_bucket_index(__prev_p->_M_next(), __n);
+	  if (__next_bkt != __prev_bkt)
+	    __new_buckets[__next_bkt] = __prev_p;
+	}
+
+      _M_deallocate_buckets();
+      _M_bucket_count = __n;
+      _M_buckets = __new_buckets;
+    }
+
+#if __cplusplus > 201402L
+  template<typename, typename, typename> class _Hash_merge_helper { };
+#endif // C++17
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+
+#endif // _HASHTABLE_H