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 /* Copyright 2003-2020 Joaquin M Lopez Munoz.
  * Distributed under the Boost Software License, Version 1.0.
  * (See accompanying file LICENSE_1_0.txt or copy at
  * http://www.boost.org/LICENSE_1_0.txt)
  *
  * See http://www.boost.org/libs/multi_index for library home page.
  */
 
 #ifndef BOOST_MULTI_INDEX_DETAIL_HASH_INDEX_NODE_HPP
 #define BOOST_MULTI_INDEX_DETAIL_HASH_INDEX_NODE_HPP
 
 #if defined(_MSC_VER)
 #pragma once
 #endif
 
 #include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
 #include <boost/multi_index/detail/allocator_traits.hpp>
 #include <boost/multi_index/detail/raw_ptr.hpp>
 #include <utility>
 
 namespace boost{
 
 namespace multi_index{
 
 namespace detail{
 
 /* Certain C++ requirements on unordered associative containers (see LWG issue
  * #579) imply a data structure where nodes are linked in a single list, which
  * in its turn forces implementors to add additional overhed per node to
  * associate each with its corresponding bucket. Others resort to storing hash
  * values, we use an alternative structure providing unconditional O(1)
  * manipulation, even in situations of unfair hash distribution, plus some
  * lookup speedups. For unique indices we maintain a doubly linked list of
  * nodes except that if N is the first node of a bucket its associated
  * bucket node is embedded between N and the preceding node in the following
  * manner:
  *
  *        +---+   +---+       +---+   +---+
  *     <--+   |<--+   |    <--+   |<--+   |
  *   ...  | B0|   | B1|  ...  | B1|   | B2|  ...
  *        |   |-+ |   +-->    |   |-+ |   +-->
  *        +-+-+ | +---+       +-+-+ | +---+
  *              |   ^               |   ^
  *              |   |               |   |
  *              | +-+               | +-+
  *              | |                 | |
  *              v |                 v |  
  *       --+---+---+---+--   --+---+---+---+--
  *     ... |   | B1|   |  ...  |   | B2|   | ...
  *       --+---+---+---+--   --+---+---+---+--
  *
  *
  * The fist and last nodes of buckets can be checked with
  *
  *   first node of a bucket: Npn != N
  *   last node of a bucket:  Nnp != N
  *
  * (n and p short for ->next(), ->prior(), bucket nodes have prior pointers
  * only). Pure insert and erase (without lookup) can be unconditionally done
  * in O(1).
  * For non-unique indices we add the following additional complexity: when
  * there is a group of 3 or more equivalent elements, they are linked as
  * follows:
  *
  *         +-----------------------+
  *         |                       v
  *   +---+ | +---+       +---+   +---+
  *   |   | +-+   |       |   |<--+   |
  *   | F |   | S |  ...  | P |   | L |
  *   |   +-->|   |       |   +-+ |   |
  *   +---+   +---+       +---+ | +---+
  *     ^                       |
  *     +-----------------------+
  * 
  * F, S, P and L are the first, second, penultimate and last node in the
  * group, respectively (S and P can coincide if the group has size 3.) This
  * arrangement is used to skip equivalent elements in O(1) when doing lookup,
  * while preserving O(1) insert/erase. The following invariants identify
  * special positions (some of the operations have to be carefully implemented
  * as Xnn is not valid if Xn points to a bucket):
  *
  *   first node of a bucket: Npnp  == N
  *   last node of a bucket:  Nnpp  == N
  *   first node of a group:  Nnp != N && Nnppn == N
  *   second node of a group: Npn != N && Nppnn == N
  *   n-1 node of a group:    Nnp != N && Nnnpp == N
  *   last node of a group:   Npn != N && Npnnp == N
  * 
  * The memory overhead is one pointer per bucket plus two pointers per node,
  * probably unbeatable. The resulting structure is bidirectonally traversable,
  * though currently we are just providing forward iteration.
  */
 
 template<typename Allocator>
 struct hashed_index_node_impl;
 
 /* half-header (only prior() pointer) to use for the bucket array */
 
 template<typename Allocator>
 struct hashed_index_base_node_impl
 {
   typedef typename rebind_alloc_for<
     Allocator,hashed_index_base_node_impl
   >::type                                             base_allocator;
   typedef typename rebind_alloc_for<
     Allocator,hashed_index_node_impl<Allocator>
   >::type                                             node_allocator;
   typedef allocator_traits<base_allocator>            base_alloc_traits;
   typedef allocator_traits<node_allocator>            node_alloc_traits;
   typedef typename base_alloc_traits::pointer         base_pointer;
   typedef typename base_alloc_traits::const_pointer   const_base_pointer;
   typedef typename node_alloc_traits::pointer         pointer;
   typedef typename node_alloc_traits::const_pointer   const_pointer;
   typedef typename node_alloc_traits::difference_type difference_type;
 
   pointer& prior(){return prior_;}
   pointer  prior()const{return prior_;}
 
 private:
   pointer prior_;
 };
 
 /* full header (prior() and next()) for the nodes */
 
 template<typename Allocator>
 struct hashed_index_node_impl:hashed_index_base_node_impl<Allocator>
 {
 private:
   typedef hashed_index_base_node_impl<Allocator> super;
 
 public:  
   typedef typename super::base_pointer           base_pointer;
   typedef typename super::const_base_pointer     const_base_pointer;
   typedef typename super::pointer                pointer;
   typedef typename super::const_pointer          const_pointer;
 
   base_pointer& next(){return next_;}
   base_pointer  next()const{return next_;}
 
   static pointer pointer_from(base_pointer x)
   {
     return static_cast<pointer>(
       static_cast<hashed_index_node_impl*>(
         raw_ptr<super*>(x)));
   }
 
   static base_pointer base_pointer_from(pointer x)
   {
     return static_cast<base_pointer>(
       raw_ptr<hashed_index_node_impl*>(x));
   }
 
 private:
   base_pointer next_;
 };
 
 /* Boost.MultiIndex requires machinery to reverse unlink operations. A simple
  * way to make a pointer-manipulation function undoable is to templatize
  * its internal pointer assignments with a functor that, besides doing the
  * assignment, keeps track of the original pointer values and can later undo
  * the operations in reverse order.
  */
 
 struct default_assigner
 {
   template<typename T> void operator()(T& x,const T& val){x=val;}
 };
 
 template<typename Node>
 struct unlink_undo_assigner
 {
   typedef typename Node::base_pointer base_pointer;
   typedef typename Node::pointer      pointer;
 
   unlink_undo_assigner():pointer_track_count(0),base_pointer_track_count(0){}
 
   void operator()(pointer& x,pointer val)
   {
     pointer_tracks[pointer_track_count].x=&x;
     pointer_tracks[pointer_track_count++].val=x;
     x=val;
   }
 
   void operator()(base_pointer& x,base_pointer val)
   {
     base_pointer_tracks[base_pointer_track_count].x=&x;
     base_pointer_tracks[base_pointer_track_count++].val=x;
     x=val;
   }
 
   void operator()() /* undo op */
   {
     /* in the absence of aliasing, restitution order is immaterial */
 
     while(pointer_track_count--){
       *(pointer_tracks[pointer_track_count].x)=
         pointer_tracks[pointer_track_count].val;
     }
     while(base_pointer_track_count--){
       *(base_pointer_tracks[base_pointer_track_count].x)=
         base_pointer_tracks[base_pointer_track_count].val;
     }
   }
 
   struct pointer_track     {pointer*      x; pointer      val;};
   struct base_pointer_track{base_pointer* x; base_pointer val;};
 
   /* We know the maximum number of pointer and base pointer assignments that
    * the two unlink versions do, so we can statically reserve the needed
    * storage.
    */
 
   pointer_track      pointer_tracks[3];
   int                pointer_track_count;
   base_pointer_track base_pointer_tracks[2];
   int                base_pointer_track_count;
 };
 
 /* algorithmic stuff for unique and non-unique variants */
 
 struct hashed_unique_tag{};
 struct hashed_non_unique_tag{};
 
 template<typename Node,typename Category>
 struct hashed_index_node_alg;
 
 template<typename Node>
 struct hashed_index_node_alg<Node,hashed_unique_tag>
 {
   typedef typename Node::base_pointer       base_pointer;
   typedef typename Node::const_base_pointer const_base_pointer;
   typedef typename Node::pointer            pointer;
   typedef typename Node::const_pointer      const_pointer;
 
   static bool is_first_of_bucket(pointer x)
   {
     return x->prior()->next()!=base_pointer_from(x);
   }
 
   static pointer after(pointer x)
   {
     return is_last_of_bucket(x)?x->next()->prior():pointer_from(x->next());
   }
 
   static pointer after_local(pointer x)
   {
     return is_last_of_bucket(x)?pointer(0):pointer_from(x->next());
   }
 
   static pointer next_to_inspect(pointer x)
   {
     return is_last_of_bucket(x)?pointer(0):pointer_from(x->next());
   }
 
   static void link(pointer x,base_pointer buc,pointer end)
   {
     if(buc->prior()==pointer(0)){ /* empty bucket */
       x->prior()=end->prior();
       x->next()=end->prior()->next();
       x->prior()->next()=buc;
       buc->prior()=x;
       end->prior()=x;
     }
     else{
       x->prior()=buc->prior()->prior();
       x->next()=base_pointer_from(buc->prior());
       buc->prior()=x;
       x->next()->prior()=x;
     }
   }
 
   static void unlink(pointer x)
   {
     default_assigner assign;
     unlink(x,assign);
   }
 
   typedef unlink_undo_assigner<Node> unlink_undo;
 
   template<typename Assigner>
   static void unlink(pointer x,Assigner& assign)
   {
     if(is_first_of_bucket(x)){
       if(is_last_of_bucket(x)){
         assign(x->prior()->next()->prior(),pointer(0));
         assign(x->prior()->next(),x->next());
         assign(x->next()->prior()->prior(),x->prior());
       }
       else{
         assign(x->prior()->next()->prior(),pointer_from(x->next()));
         assign(x->next()->prior(),x->prior());
       }
     }
     else if(is_last_of_bucket(x)){
       assign(x->prior()->next(),x->next());
       assign(x->next()->prior()->prior(),x->prior());
     }
     else{
       assign(x->prior()->next(),x->next());
       assign(x->next()->prior(),x->prior());
     }
   }
 
   /* used only at rehashing */
 
   static void append(pointer x,pointer end)
   {
     x->prior()=end->prior();
     x->next()=end->prior()->next();
     x->prior()->next()=base_pointer_from(x);
     end->prior()=x;
   }
 
   static bool unlink_last(pointer end)
   {
     /* returns true iff bucket is emptied */
 
     pointer x=end->prior();
     if(x->prior()->next()==base_pointer_from(x)){
       x->prior()->next()=x->next();
       end->prior()=x->prior();
       return false;
     }
     else{
       x->prior()->next()->prior()=pointer(0);
       x->prior()->next()=x->next();
       end->prior()=x->prior();
       return true;
     }
   }
 
 private:
   static pointer pointer_from(base_pointer x)
   {
     return Node::pointer_from(x);
   }
 
   static base_pointer base_pointer_from(pointer x)
   {
     return Node::base_pointer_from(x);
   }
 
   static bool is_last_of_bucket(pointer x)
   {
     return x->next()->prior()!=x;
   }
 };
 
 template<typename Node>
 struct hashed_index_node_alg<Node,hashed_non_unique_tag>
 {
   typedef typename Node::base_pointer       base_pointer;
   typedef typename Node::const_base_pointer const_base_pointer;
   typedef typename Node::pointer            pointer;
   typedef typename Node::const_pointer      const_pointer;
 
   static bool is_first_of_bucket(pointer x)
   {
     return x->prior()->next()->prior()==x;
   }
 
   static bool is_first_of_group(pointer x)
   {
     return
       x->next()->prior()!=x&&
       x->next()->prior()->prior()->next()==base_pointer_from(x);
   }
 
   static pointer after(pointer x)
   {
     if(x->next()->prior()==x)return pointer_from(x->next());
     if(x->next()->prior()->prior()==x)return x->next()->prior();
     if(x->next()->prior()->prior()->next()==base_pointer_from(x))
       return pointer_from(x->next());
     return pointer_from(x->next())->next()->prior();
   }
 
   static pointer after_local(pointer x)
   {
     if(x->next()->prior()==x)return pointer_from(x->next());
     if(x->next()->prior()->prior()==x)return pointer(0);
     if(x->next()->prior()->prior()->next()==base_pointer_from(x))
       return pointer_from(x->next());
     return pointer_from(x->next())->next()->prior();
   }
 
   static pointer next_to_inspect(pointer x)
   {
     if(x->next()->prior()==x)return pointer_from(x->next());
     if(x->next()->prior()->prior()==x)return pointer(0);
     if(x->next()->prior()->next()->prior()!=x->next()->prior())
       return pointer(0);
     return pointer_from(x->next()->prior()->next());
   }
 
   static void link(pointer x,base_pointer buc,pointer end)
   {
     if(buc->prior()==pointer(0)){ /* empty bucket */
       x->prior()=end->prior();
       x->next()=end->prior()->next();
       x->prior()->next()=buc;
       buc->prior()=x;
       end->prior()=x;
     }
     else{
       x->prior()=buc->prior()->prior();
       x->next()=base_pointer_from(buc->prior());
       buc->prior()=x;
       x->next()->prior()=x;
     }
   }
 
   static void link(pointer x,pointer first,pointer last)
   {
     x->prior()=first->prior();
     x->next()=base_pointer_from(first);
     if(is_first_of_bucket(first)){
       x->prior()->next()->prior()=x;
     }
     else{
       x->prior()->next()=base_pointer_from(x);
     }
 
     if(first==last){
       last->prior()=x;
     }
     else if(first->next()==base_pointer_from(last)){
       first->prior()=last;
       first->next()=base_pointer_from(x);
     }
     else{
       pointer second=pointer_from(first->next()),
               lastbutone=last->prior();
       second->prior()=first;
       first->prior()=last;
       lastbutone->next()=base_pointer_from(x);
     }
   }
 
   static void unlink(pointer x)
   {
     default_assigner assign;
     unlink(x,assign);
   }
 
   typedef unlink_undo_assigner<Node> unlink_undo;
 
   template<typename Assigner>
   static void unlink(pointer x,Assigner& assign)
   {
     if(x->prior()->next()==base_pointer_from(x)){
       if(x->next()->prior()==x){
         left_unlink(x,assign);
         right_unlink(x,assign);
       }
       else if(x->next()->prior()->prior()==x){           /* last of bucket */
         left_unlink(x,assign);
         right_unlink_last_of_bucket(x,assign);
       }
       else if(x->next()->prior()->prior()->next()==
               base_pointer_from(x)){                /* first of group size */
         left_unlink(x,assign);
         right_unlink_first_of_group(x,assign);
       }
       else{                                                /* n-1 of group */
         unlink_last_but_one_of_group(x,assign);
       }
     }
     else if(x->prior()->next()->prior()==x){            /* first of bucket */
       if(x->next()->prior()==x){
         left_unlink_first_of_bucket(x,assign);
         right_unlink(x,assign);
       }
       else if(x->next()->prior()->prior()==x){           /* last of bucket */
         assign(x->prior()->next()->prior(),pointer(0));
         assign(x->prior()->next(),x->next());
         assign(x->next()->prior()->prior(),x->prior());
       }
       else{                                              /* first of group */
         left_unlink_first_of_bucket(x,assign);
         right_unlink_first_of_group(x,assign);
       }
     }
     else if(x->next()->prior()->prior()==x){   /* last of group and bucket */
       left_unlink_last_of_group(x,assign);
       right_unlink_last_of_bucket(x,assign);
     }
     else if(pointer_from(x->prior()->prior()->next())
             ->next()==base_pointer_from(x)){            /* second of group */
       unlink_second_of_group(x,assign);
     }
     else{                              /* last of group, ~(last of bucket) */
       left_unlink_last_of_group(x,assign);
       right_unlink(x,assign);
     }
   }
 
   /* used only at rehashing */
 
   static void link_range(
     pointer first,pointer last,base_pointer buc,pointer cend)
   {
     if(buc->prior()==pointer(0)){ /* empty bucket */
       first->prior()=cend->prior();
       last->next()=cend->prior()->next();
       first->prior()->next()=buc;
       buc->prior()=first;
       cend->prior()=last;
     }
     else{
       first->prior()=buc->prior()->prior();
       last->next()=base_pointer_from(buc->prior());
       buc->prior()=first;
       last->next()->prior()=last;
     }
   }
 
   static void append_range(pointer first,pointer last,pointer cend)
   {
     first->prior()=cend->prior();
     last->next()=cend->prior()->next();
     first->prior()->next()=base_pointer_from(first);
     cend->prior()=last;
   }
 
   static std::pair<pointer,bool> unlink_last_group(pointer end)
   {
     /* returns first of group true iff bucket is emptied */
 
     pointer x=end->prior();
     if(x->prior()->next()==base_pointer_from(x)){
       x->prior()->next()=x->next();
       end->prior()=x->prior();
       return std::make_pair(x,false);
     }
     else if(x->prior()->next()->prior()==x){
       x->prior()->next()->prior()=pointer(0);
       x->prior()->next()=x->next();
       end->prior()=x->prior();
       return std::make_pair(x,true);
     }
     else{
       pointer y=pointer_from(x->prior()->next());
 
       if(y->prior()->next()==base_pointer_from(y)){
         y->prior()->next()=x->next();
         end->prior()=y->prior();
         return std::make_pair(y,false);
       }
       else{
         y->prior()->next()->prior()=pointer(0);
         y->prior()->next()=x->next();
         end->prior()=y->prior();
         return std::make_pair(y,true);
       }
     }
   }
 
   static void unlink_range(pointer first,pointer last)
   {
     if(is_first_of_bucket(first)){
       if(is_last_of_bucket(last)){
         first->prior()->next()->prior()=pointer(0);
         first->prior()->next()=last->next();
         last->next()->prior()->prior()=first->prior();
       }
       else{
         first->prior()->next()->prior()=pointer_from(last->next());
         last->next()->prior()=first->prior();
       }
     }
     else if(is_last_of_bucket(last)){
       first->prior()->next()=last->next();
       last->next()->prior()->prior()=first->prior();
     }
     else{
       first->prior()->next()=last->next();
       last->next()->prior()=first->prior();
     }
   }
 
 private:
   static pointer pointer_from(base_pointer x)
   {
     return Node::pointer_from(x);
   }
 
   static base_pointer base_pointer_from(pointer x)
   {
     return Node::base_pointer_from(x);
   }
 
   static bool is_last_of_bucket(pointer x)
   {
     return x->next()->prior()->prior()==x;
   }
 
   template<typename Assigner>
   static void left_unlink(pointer x,Assigner& assign)
   {
     assign(x->prior()->next(),x->next());
   }
   
   template<typename Assigner>
   static void right_unlink(pointer x,Assigner& assign)
   {
     assign(x->next()->prior(),x->prior());
   }
 
   template<typename Assigner>
   static void left_unlink_first_of_bucket(pointer x,Assigner& assign)
   {
     assign(x->prior()->next()->prior(),pointer_from(x->next()));
   }
 
   template<typename Assigner>
   static void right_unlink_last_of_bucket(pointer x,Assigner& assign)
   {
     assign(x->next()->prior()->prior(),x->prior());
   }
 
   template<typename Assigner>
   static void right_unlink_first_of_group(pointer x,Assigner& assign)
   {
     pointer second=pointer_from(x->next()),
             last=second->prior(),
             lastbutone=last->prior();
     if(second==lastbutone){
       assign(second->next(),base_pointer_from(last));
       assign(second->prior(),x->prior());
     }
     else{
       assign(lastbutone->next(),base_pointer_from(second));
       assign(second->next()->prior(),last);
       assign(second->prior(),x->prior());
     }
   }
 
   template<typename Assigner>
   static void left_unlink_last_of_group(pointer x,Assigner& assign)
   {
     pointer lastbutone=x->prior(),
             first=pointer_from(lastbutone->next()),
             second=pointer_from(first->next());
     if(lastbutone==second){
       assign(lastbutone->prior(),first);
       assign(lastbutone->next(),x->next());
     }
     else{
       assign(second->prior(),lastbutone);
       assign(lastbutone->prior()->next(),base_pointer_from(first));
       assign(lastbutone->next(),x->next());
     }
   }
 
   template<typename Assigner>
   static void unlink_last_but_one_of_group(pointer x,Assigner& assign)
   {
     pointer first=pointer_from(x->next()),
             second=pointer_from(first->next()),
             last=second->prior();
     if(second==x){
       assign(last->prior(),first);
       assign(first->next(),base_pointer_from(last));
     }
     else{
       assign(last->prior(),x->prior());
       assign(x->prior()->next(),base_pointer_from(first));
     }
   }
 
   template<typename Assigner>
   static void unlink_second_of_group(pointer x,Assigner& assign)
   {
     pointer last=x->prior(),
             lastbutone=last->prior(),
             first=pointer_from(lastbutone->next());
     if(lastbutone==x){
       assign(first->next(),base_pointer_from(last));
       assign(last->prior(),first);
     }
     else{
       assign(first->next(),x->next());
       assign(x->next()->prior(),last);
     }
   }
 };
 
 template<typename Super>
 struct hashed_index_node_trampoline:
   hashed_index_node_impl<
     typename rebind_alloc_for<
       typename Super::allocator_type,char
     >::type
   >
 {
   typedef typename rebind_alloc_for<
     typename Super::allocator_type,char
   >::type                                             impl_allocator_type;
   typedef hashed_index_node_impl<impl_allocator_type> impl_type;
 };
 
 template<typename Super>
 struct hashed_index_node:
   Super,hashed_index_node_trampoline<Super>
 {
 private:
   typedef hashed_index_node_trampoline<Super> trampoline;
 
 public:
   typedef typename trampoline::impl_type          impl_type;
   typedef typename trampoline::base_pointer       impl_base_pointer;
   typedef typename trampoline::const_base_pointer const_impl_base_pointer;
   typedef typename trampoline::pointer            impl_pointer;
   typedef typename trampoline::const_pointer      const_impl_pointer;
   typedef typename trampoline::difference_type    difference_type;
 
   template<typename Category>
   struct node_alg{
     typedef hashed_index_node_alg<impl_type,Category> type;
   };
 
   impl_pointer&      prior(){return trampoline::prior();}
   impl_pointer       prior()const{return trampoline::prior();}
   impl_base_pointer& next(){return trampoline::next();}
   impl_base_pointer  next()const{return trampoline::next();}
 
   impl_pointer impl()
   {
     return static_cast<impl_pointer>(
       static_cast<impl_type*>(static_cast<trampoline*>(this)));
   }
 
   const_impl_pointer impl()const
   {
     return static_cast<const_impl_pointer>(
       static_cast<const impl_type*>(static_cast<const trampoline*>(this)));
   }
 
   static hashed_index_node* from_impl(impl_pointer x)
   {
     return
       static_cast<hashed_index_node*>(
         static_cast<trampoline*>(
           raw_ptr<impl_type*>(x)));
   }
 
   static const hashed_index_node* from_impl(const_impl_pointer x)
   {
     return 
       static_cast<const hashed_index_node*>(
         static_cast<const trampoline*>(
           raw_ptr<const impl_type*>(x)));
   }
 
   /* interoperability with hashed_index_iterator */
 
   template<typename Category>
   static void increment(hashed_index_node*& x)
   {
     x=from_impl(node_alg<Category>::type::after(x->impl()));
   }
 
   template<typename Category>
   static void increment_local(hashed_index_node*& x)
   {
     x=from_impl(node_alg<Category>::type::after_local(x->impl()));
   }
 };
 
 } /* namespace multi_index::detail */
 
 } /* namespace multi_index */
 
 } /* namespace boost */
 
 #endif

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