fsfw/contrib/fsfw_contrib/etl-20.39.4/include/etl/unordered_multiset.h

///\file

/******************************************************************************
The MIT License(MIT)

Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com

Copyright(c) 2016 John Wellbelove

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files(the "Software"), to deal
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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******************************************************************************/

#ifndef ETL_UNORDERED_MULTISET_INCLUDED
#define ETL_UNORDERED_MULTISET_INCLUDED

#include "platform.h"
#include "algorithm.h"
#include "iterator.h"
#include "functional.h"
#include "utility.h"
#include "pool.h"
#include "vector.h"
#include "intrusive_forward_list.h"
#include "hash.h"
#include "type_traits.h"
#include "nth_type.h"
#include "parameter_type.h"
#include "nullptr.h"
#include "error_handler.h"
#include "exception.h"
#include "debug_count.h"
#include "iterator.h"
#include "placement_new.h"
#include "initializer_list.h"

#include <stddef.h>

//*****************************************************************************
///\defgroup unordered_multiset unordered_multiset
/// A unordered_multiset with the capacity defined at compile time.
///\ingroup containers
//*****************************************************************************

namespace etl
{
  //***************************************************************************
  /// Exception for the unordered_multiset.
  ///\ingroup unordered_multiset
  //***************************************************************************
  class unordered_multiset_exception : public etl::exception
  {
  public:

    unordered_multiset_exception(string_type reason_, string_type file_name_, numeric_type line_number_)
      : etl::exception(reason_, file_name_, line_number_)
    {
    }
  };

  //***************************************************************************
  /// Full exception for the unordered_multiset.
  ///\ingroup unordered_multiset
  //***************************************************************************
  class unordered_multiset_full : public etl::unordered_multiset_exception
  {
  public:

    unordered_multiset_full(string_type file_name_, numeric_type line_number_)
      : etl::unordered_multiset_exception(ETL_ERROR_TEXT("unordered_multiset:full", ETL_UNORDERED_MULTISET_FILE_ID"A"), file_name_, line_number_)
    {
    }
  };

  //***************************************************************************
  /// Out of range exception for the unordered_multiset.
  ///\ingroup unordered_multiset
  //***************************************************************************
  class unordered_multiset_out_of_range : public etl::unordered_multiset_exception
  {
  public:

    unordered_multiset_out_of_range(string_type file_name_, numeric_type line_number_)
      : etl::unordered_multiset_exception(ETL_ERROR_TEXT("unordered_multiset:range", ETL_UNORDERED_MULTISET_FILE_ID"B"), file_name_, line_number_)
    {}
  };

  //***************************************************************************
  /// Iterator exception for the unordered_multiset.
  ///\ingroup unordered_multiset
  //***************************************************************************
  class unordered_multiset_iterator : public etl::unordered_multiset_exception
  {
  public:

    unordered_multiset_iterator(string_type file_name_, numeric_type line_number_)
      : etl::unordered_multiset_exception(ETL_ERROR_TEXT("unordered_multiset:iterator", ETL_UNORDERED_MULTISET_FILE_ID"C"), file_name_, line_number_)
    {
    }
  };

  //***************************************************************************
  /// The base class for specifically sized unordered_multiset.
  /// Can be used as a reference type for all unordered_multiset containing a specific type.
  ///\ingroup unordered_multiset
  //***************************************************************************
  template <typename TKey, typename THash = etl::hash<TKey>, typename TKeyEqual = etl::equal_to<TKey> >
  class iunordered_multiset
  {
  public:

    typedef TKey              value_type;
    typedef TKey              key_type;
    typedef THash             hasher;
    typedef TKeyEqual         key_equal;
    typedef value_type&       reference;
    typedef const value_type& const_reference;
#if ETL_USING_CPP11
    typedef value_type&&      rvalue_reference;
#endif
    typedef value_type*       pointer;
    typedef const value_type* const_pointer;
    typedef size_t            size_type;

    typedef const TKey& key_parameter_t;

    typedef etl::forward_link<0> link_t;

    //*********************************************************************
    // The nodes that store the elements.
    struct node_t : public link_t
    {
      node_t(const_reference key_)
        : key(key_)
      {
      }

      value_type key;
    };

    friend bool operator ==(const node_t& lhs, const node_t& rhs)
    {
      return (lhs.key == rhs.key);
    }

    friend bool operator !=(const node_t& lhs, const node_t& rhs)
    {
      return !(lhs == rhs);
    }

  protected:

    typedef etl::intrusive_forward_list<node_t, link_t> bucket_t;
    typedef etl::ipool pool_t;

  public:

    // Local iterators iterate over one bucket.
    typedef typename bucket_t::iterator       local_iterator;
    typedef typename bucket_t::const_iterator const_local_iterator;

    //*********************************************************************
    class iterator : public etl::iterator<ETL_OR_STD::forward_iterator_tag, TKey>
    {
    public:

      typedef typename etl::iterator<ETL_OR_STD::forward_iterator_tag, TKey>::value_type value_type;
      typedef typename iunordered_multiset::key_type        key_type;
      typedef typename iunordered_multiset::hasher          hasher;
      typedef typename iunordered_multiset::key_equal       key_equal;
      typedef typename iunordered_multiset::reference       reference;
      typedef typename iunordered_multiset::const_reference const_reference;
      typedef typename iunordered_multiset::pointer         pointer;
      typedef typename iunordered_multiset::const_pointer   const_pointer;
      typedef typename iunordered_multiset::size_type       size_type;

      friend class iunordered_multiset;
      friend class const_iterator;

      //*********************************
      iterator()
      {
      }

      //*********************************
      iterator(const iterator& other)
        : pbuckets_end(other.pbuckets_end)
        , pbucket(other.pbucket)
        , inode(other.inode)
      {
      }

      //*********************************
      iterator& operator ++()
      {
        ++inode;

        // The end of this node list?
        if (inode == pbucket->end())
        {
          // Search for the next non-empty bucket.
          ++pbucket;
          while ((pbucket != pbuckets_end) && (pbucket->empty()))
          {
            ++pbucket;
          }

          // If not past the end, get the first node in the bucket.
          if (pbucket != pbuckets_end)
          {
            inode = pbucket->begin();
          }
        }

        return *this;
      }

      //*********************************
      iterator operator ++(int)
      {
        iterator temp(*this);
        operator++();
        return temp;
      }

      //*********************************
      iterator& operator =(const iterator& other)
      {
        pbuckets_end = other.pbuckets_end;
        pbucket = other.pbucket;
        inode = other.inode;
        return *this;
      }

      //*********************************
      reference operator *() const
      {
        return inode->key;
      }

      //*********************************
      pointer operator &() const
      {
        return &(inode->key);
      }

      //*********************************
      pointer operator ->() const
      {
        return &(inode->key);
      }

      //*********************************
      friend bool operator == (const iterator& lhs, const iterator& rhs)
      {
        return lhs.compare(rhs);
      }

      //*********************************
      friend bool operator != (const iterator& lhs, const iterator& rhs)
      {
        return !(lhs == rhs);
      }

    private:

      //*********************************
      iterator(bucket_t* pbuckets_end_, bucket_t* pbucket_, local_iterator inode_)
        : pbuckets_end(pbuckets_end_)
        , pbucket(pbucket_)
        , inode(inode_)
      {
      }

      //*********************************
      bool compare(const iterator& rhs) const
      {
        return rhs.inode == inode;
      }

      //*********************************
      bucket_t& get_bucket()
      {
        return *pbucket;
      }

      //*********************************
      bucket_t*& get_bucket_list_iterator()
      {
        return pbucket;
      }

      //*********************************
      local_iterator get_local_iterator()
      {
        return inode;
      }

      bucket_t* pbuckets_end;
      bucket_t* pbucket;
      local_iterator inode;
    };

    //*********************************************************************
    class const_iterator : public etl::iterator<ETL_OR_STD::forward_iterator_tag, const TKey>
    {
    public:

      typedef typename etl::iterator<ETL_OR_STD::forward_iterator_tag, const TKey>::value_type value_type;
      typedef typename iunordered_multiset::key_type        key_type;
      typedef typename iunordered_multiset::hasher          hasher;
      typedef typename iunordered_multiset::key_equal       key_equal;
      typedef typename iunordered_multiset::reference       reference;
      typedef typename iunordered_multiset::const_reference const_reference;
      typedef typename iunordered_multiset::pointer         pointer;
      typedef typename iunordered_multiset::const_pointer   const_pointer;
      typedef typename iunordered_multiset::size_type       size_type;

      friend class iunordered_multiset;
      friend class iterator;

      //*********************************
      const_iterator()
      {
      }

      //*********************************
      const_iterator(const typename iunordered_multiset::iterator& other)
        : pbuckets_end(other.pbuckets_end)
        , pbucket(other.pbucket)
        , inode(other.inode)
      {
      }

      //*********************************
      const_iterator(const const_iterator& other)
        : pbuckets_end(other.pbuckets_end)
        , pbucket(other.pbucket)
        , inode(other.inode)
      {
      }

      //*********************************
      const_iterator& operator ++()
      {
        ++inode;

        // The end of this node list?
        if (inode == pbucket->end())
        {
          // Search for the next non-empty bucket.

          ++pbucket;
          while ((pbucket != pbuckets_end) && (pbucket->empty()))
          {
            ++pbucket;
          }

          // If not past the end, get the first node in the bucket.
          if (pbucket != pbuckets_end)
          {
            inode = pbucket->begin();
          }
        }

        return *this;
      }

      //*********************************
      const_iterator operator ++(int)
      {
        const_iterator temp(*this);
        operator++();
        return temp;
      }

      //*********************************
      const_iterator& operator =(const const_iterator& other)
      {
        pbuckets_end = other.pbuckets_end;
        pbucket = other.pbucket;
        inode = other.inode;
        return *this;
      }

      //*********************************
      const_reference operator *() const
      {
        return inode->key;
      }

      //*********************************
      const_pointer operator &() const
      {
        return &(inode->key);
      }

      //*********************************
      const_pointer operator ->() const
      {
        return &(inode->key);
      }

      //*********************************
      friend bool operator == (const const_iterator& lhs, const const_iterator& rhs)
      {
        return lhs.compare(rhs);
      }

      //*********************************
      friend bool operator != (const const_iterator& lhs, const const_iterator& rhs)
      {
        return !(lhs == rhs);
      }

    private:

      //*********************************
      const_iterator(bucket_t* pbuckets_end_, bucket_t* pbucket_, local_iterator inode_)
        : pbuckets_end(pbuckets_end_)
        , pbucket(pbucket_)
        , inode(inode_)
      {
      }

      //*********************************
      bool compare(const const_iterator& rhs) const
      {
        return rhs.inode == inode;
      }

      //*********************************
      bucket_t& get_bucket()
      {
        return *pbucket;
      }

      //*********************************
      bucket_t*& get_bucket_list_iterator()
      {
        return pbucket;
      }

      //*********************************
      local_iterator get_local_iterator()
      {
        return inode;
      }

      bucket_t* pbuckets_end;
      bucket_t* pbucket;
      local_iterator inode;
    };

    typedef typename etl::iterator_traits<iterator>::difference_type difference_type;

    //*********************************************************************
    /// Returns an iterator to the beginning of the unordered_multiset.
    ///\return An iterator to the beginning of the unordered_multiset.
    //*********************************************************************
    iterator begin()
    {
      return iterator((pbuckets + number_of_buckets), first, first->begin());
    }

    //*********************************************************************
    /// Returns a const_iterator to the beginning of the unordered_multiset.
    ///\return A const iterator to the beginning of the unordered_multiset.
    //*********************************************************************
    const_iterator begin() const
    {
      return const_iterator((pbuckets + number_of_buckets), first, first->begin());
    }

    //*********************************************************************
    /// Returns a const_iterator to the beginning of the unordered_multiset.
    ///\return A const iterator to the beginning of the unordered_multiset.
    //*********************************************************************
    const_iterator cbegin() const
    {
      return const_iterator((pbuckets + number_of_buckets), first, first->begin());
    }

    //*********************************************************************
    /// Returns an iterator to the beginning of the unordered_multiset bucket.
    ///\return An iterator to the beginning of the unordered_multiset bucket.
    //*********************************************************************
    local_iterator begin(size_t i)
    {
      return pbuckets[i].begin();
    }

    //*********************************************************************
    /// Returns a const_iterator to the beginning of the unordered_multiset bucket.
    ///\return A const iterator to the beginning of the unordered_multiset bucket.
    //*********************************************************************
    const_local_iterator begin(size_t i) const
    {
      return pbuckets[i].cbegin();
    }

    //*********************************************************************
    /// Returns a const_iterator to the beginning of the unordered_multiset bucket.
    ///\return A const iterator to the beginning of the unordered_multiset bucket.
    //*********************************************************************
    const_local_iterator cbegin(size_t i) const
    {
      return pbuckets[i].cbegin();
    }

    //*********************************************************************
    /// Returns an iterator to the end of the unordered_multiset.
    ///\return An iterator to the end of the unordered_multiset.
    //*********************************************************************
    iterator end()
    {
      return iterator((pbuckets + number_of_buckets), last, last->end());
    }

    //*********************************************************************
    /// Returns a const_iterator to the end of the unordered_multiset.
    ///\return A const iterator to the end of the unordered_multiset.
    //*********************************************************************
    const_iterator end() const
    {
      return const_iterator((pbuckets + number_of_buckets), last, last->end());
    }

    //*********************************************************************
    /// Returns a const_iterator to the end of the unordered_multiset.
    ///\return A const iterator to the end of the unordered_multiset.
    //*********************************************************************
    const_iterator cend() const
    {
      return const_iterator((pbuckets + number_of_buckets), last, last->end());
    }

    //*********************************************************************
    /// Returns an iterator to the end of the unordered_multiset bucket.
    ///\return An iterator to the end of the unordered_multiset bucket.
    //*********************************************************************
    local_iterator end(size_t i)
    {
      return pbuckets[i].end();
    }

    //*********************************************************************
    /// Returns a const_iterator to the end of the unordered_multiset bucket.
    ///\return A const iterator to the end of the unordered_multiset bucket.
    //*********************************************************************
    const_local_iterator end(size_t i) const
    {
      return pbuckets[i].cend();
    }

    //*********************************************************************
    /// Returns a const_iterator to the end of the unordered_multiset bucket.
    ///\return A const iterator to the end of the unordered_multiset bucket.
    //*********************************************************************
    const_local_iterator cend(size_t i) const
    {
      return pbuckets[i].cend();
    }

    //*********************************************************************
    /// Returns the bucket index for the key.
    ///\return The bucket index for the key.
    //*********************************************************************
    size_type get_bucket_index(key_parameter_t key) const
    {
      return key_hash_function(key) % number_of_buckets;
    }

    //*********************************************************************
    /// Returns the size of the bucket key.
    ///\return The bucket size of the bucket key.
    //*********************************************************************
    size_type bucket_size(key_parameter_t key) const
    {
      size_t index = bucket(key);

      return etl::distance(pbuckets[index].begin(), pbuckets[index].end());
    }

    //*********************************************************************
    /// Returns the maximum number of the buckets the container can hold.
    ///\return The maximum number of the buckets the container can hold.
    //*********************************************************************
    size_type max_bucket_count() const
    {
      return number_of_buckets;
    }

    //*********************************************************************
    /// Returns the number of the buckets the container holds.
    ///\return The number of the buckets the container holds.
    //*********************************************************************
    size_type bucket_count() const
    {
      return number_of_buckets;
    }

    //*********************************************************************
    /// Assigns values to the unordered_multiset.
    /// If asserts or exceptions are enabled, emits unordered_multiset_full if the unordered_multiset does not have enough free space.
    /// If asserts or exceptions are enabled, emits unordered_multiset_iterator if the iterators are reversed.
    ///\param first The iterator to the first element.
    ///\param last  The iterator to the last element + 1.
    //*********************************************************************
    template <typename TIterator>
    void assign(TIterator first_, TIterator last_)
    {
#if ETL_IS_DEBUG_BUILD
      difference_type d = etl::distance(first_, last_);
      ETL_ASSERT(d >= 0, ETL_ERROR(unordered_multiset_iterator));
      ETL_ASSERT(size_t(d) <= max_size(), ETL_ERROR(unordered_multiset_full));
#endif

      clear();

      while (first_ != last_)
      {
        insert(*first_);
        ++first_;
      }
    }

    //*********************************************************************
    /// Inserts a value to the unordered_multiset.
    /// If asserts or exceptions are enabled, emits unordered_multiset_full if the unordered_multiset is already full.
    ///\param value The value to insert.
    //*********************************************************************
    ETL_OR_STD::pair<iterator, bool> insert(const_reference key)
    {
      ETL_OR_STD::pair<iterator, bool> result(end(), false);

      ETL_ASSERT(!full(), ETL_ERROR(unordered_multiset_full));

      // Get the hash index.
      size_t index = get_bucket_index(key);

      // Get the bucket & bucket iterator.
      bucket_t* pbucket = pbuckets + index;
      bucket_t& bucket = *pbucket;

      // The first one in the bucket?
      if (bucket.empty())
      {
        // Get a new node.
        node_t* node = allocate_data_node();
        node->clear();
        ::new (&node->key) value_type(key);
        ETL_INCREMENT_DEBUG_COUNT;

        // Just add the pointer to the bucket;
        bucket.insert_after(bucket.before_begin(), *node);
        adjust_first_last_markers_after_insert(&bucket);

        result.first = iterator((pbuckets + number_of_buckets), pbucket, pbucket->begin());
        result.second = true;
      }
      else
      {
        // Step though the bucket looking for a place to insert.
        local_iterator inode_previous = bucket.before_begin();
        local_iterator inode = bucket.begin();

        while (inode != bucket.end())
        {
          // Do we already have this key?
          if (key_equal_function(inode->key, key))
          {
            break;
          }

          ++inode_previous;
          ++inode;
        }

        // Get a new node.
        node_t* node = allocate_data_node();
        node->clear();
        ::new (&node->key) value_type(key);
        ETL_INCREMENT_DEBUG_COUNT;

        // Add the node to the end of the bucket;
        bucket.insert_after(inode_previous, *node);
        adjust_first_last_markers_after_insert(&bucket);
        ++inode_previous;

        result.first = iterator((pbuckets + number_of_buckets), pbucket, inode_previous);
        result.second = true;
      }

      return result;
    }

#if ETL_USING_CPP11
    //*********************************************************************
    /// Inserts a value to the unordered_multiset.
    /// If asserts or exceptions are enabled, emits unordered_multiset_full if the unordered_multiset is already full.
    ///\param value The value to insert.
    //*********************************************************************
    ETL_OR_STD::pair<iterator, bool> insert(rvalue_reference key)
    {
      ETL_OR_STD::pair<iterator, bool> result(end(), false);

      ETL_ASSERT(!full(), ETL_ERROR(unordered_multiset_full));

      // Get the hash index.
      size_t index = get_bucket_index(key);

      // Get the bucket & bucket iterator.
      bucket_t* pbucket = pbuckets + index;
      bucket_t& bucket = *pbucket;

      // The first one in the bucket?
      if (bucket.empty())
      {
        // Get a new node.
        node_t* node = allocate_data_node();
        node->clear();
        ::new (&node->key) value_type(etl::move(key));
        ETL_INCREMENT_DEBUG_COUNT;

        // Just add the pointer to the bucket;
        bucket.insert_after(bucket.before_begin(), *node);
        adjust_first_last_markers_after_insert(&bucket);

        result.first = iterator((pbuckets + number_of_buckets), pbucket, pbucket->begin());
        result.second = true;
      }
      else
      {
        // Step though the bucket looking for a place to insert.
        local_iterator inode_previous = bucket.before_begin();
        local_iterator inode = bucket.begin();

        while (inode != bucket.end())
        {
          // Do we already have this key?
          if (key_equal_function(inode->key, key))
          {
            break;
          }

          ++inode_previous;
          ++inode;
        }

        // Get a new node.
        node_t* node = allocate_data_node();
        node->clear();
        ::new (&node->key) value_type(etl::move(key));
        ETL_INCREMENT_DEBUG_COUNT;

          // Add the node to the end of the bucket;
          bucket.insert_after(inode_previous, *node);
        adjust_first_last_markers_after_insert(&bucket);
        ++inode_previous;

        result.first = iterator((pbuckets + number_of_buckets), pbucket, inode_previous);
        result.second = true;
      }

      return result;
    }
#endif

    //*********************************************************************
    /// Inserts a value to the unordered_multiset.
    /// If asserts or exceptions are enabled, emits unordered_multiset_full if the unordered_multiset is already full.
    ///\param position The position to insert at.
    ///\param value    The value to insert.
    //*********************************************************************
    iterator insert(const_iterator /*position*/, const_reference key)
    {
      return insert(key).first;
    }

    //*********************************************************************
    /// Inserts a range of values to the unordered_multiset.
    /// If asserts or exceptions are enabled, emits unordered_multiset_full if the unordered_multiset does not have enough free space.
    ///\param position The position to insert at.
    ///\param first    The first element to add.
    ///\param last     The last + 1 element to add.
    //*********************************************************************
    template <class TIterator>
    void insert(TIterator first_, TIterator last_)
    {
      while (first_ != last_)
      {
        insert(*first_);
        ++first_;
      }
    }

    //*********************************************************************
    /// Erases an element.
    ///\param key The key to erase.
    ///\return The number of elements erased.
    //*********************************************************************
    size_t erase(key_parameter_t key)
    {
      size_t n = 0UL;
      size_t bucket_id = get_bucket_index(key);

      bucket_t& bucket = pbuckets[bucket_id];

      local_iterator iprevious = bucket.before_begin();
      local_iterator icurrent = bucket.begin();

      while (icurrent != bucket.end())
      {
        if (key_equal_function(icurrent->key, key))
        {
          delete_data_node(iprevious, icurrent, bucket);
          ++n;
          icurrent = iprevious;
        }
        else
        {
          ++iprevious;
        }

        ++icurrent;
      }

      return n;
    }

    //*********************************************************************
    /// Erases an element.
    ///\param ielement Iterator to the element.
    //*********************************************************************
    iterator erase(const_iterator ielement)
    {
      // Make a note of the next one.
      iterator inext((pbuckets + number_of_buckets), ielement.get_bucket_list_iterator(), ielement.get_local_iterator());
      ++inext;

      bucket_t&      bucket = ielement.get_bucket();
      local_iterator iprevious = bucket.before_begin();
      local_iterator icurrent = ielement.get_local_iterator();

      // Find the node previous to the one we're interested in.
      while (iprevious->etl_next != &*icurrent)
      {
        ++iprevious;
      }

      delete_data_node(iprevious, icurrent, bucket);

      return inext;
    }

    //*********************************************************************
    /// Erases a range of elements.
    /// The range includes all the elements between first and last, including the
    /// element pointed by first, but not the one pointed to by last.
    ///\param first Iterator to the first element.
    ///\param last  Iterator to the last element.
    //*********************************************************************
    iterator erase(const_iterator first_, const_iterator last_)
    {
      // Erasing everything?
      if ((first_ == begin()) && (last_ == end()))
      {
        clear();
        return end();
      }

      // Get the starting point.
      bucket_t*      pbucket     = first_.get_bucket_list_iterator();
      bucket_t*      pend_bucket = last_.get_bucket_list_iterator();
      local_iterator iprevious   = pbucket->before_begin();
      local_iterator icurrent    = first_.get_local_iterator();
      local_iterator iend        = last_.get_local_iterator(); // Note: May not be in the same bucket as icurrent.

      // Find the node previous to the first one.
      while (iprevious->etl_next != &*icurrent)
      {
        ++iprevious;
      }

      // Remember the item before the first erased one.
      iterator ibefore_erased = iterator((pbuckets + number_of_buckets), pbucket, iprevious);

      // Until we reach the end.
      while ((icurrent != iend) || (pbucket != pend_bucket))
      {
        icurrent = delete_data_node(iprevious, icurrent, *pbucket);

        // Have we not reached the end?
        if ((icurrent != iend) || (pbucket != pend_bucket))
        {
          // At the end of this bucket?
          if ((icurrent == pbucket->end()))
          {
            // Find the next non-empty one.
            do
            {
              ++pbucket;
            } while (pbucket->empty());

            iprevious = pbucket->before_begin();
            icurrent  = pbucket->begin();
          }
        }
      }

      return ++ibefore_erased;
    }

    //*************************************************************************
    /// Clears the unordered_multiset.
    //*************************************************************************
    void clear()
    {
      initialise();
    }

    //*********************************************************************
    /// Counts an element.
    ///\param key The key to search for.
    ///\return 1 if the key exists, otherwise 0.
    //*********************************************************************
    size_t count(key_parameter_t key) const
    {
      size_t n = 0UL;
      const_iterator f = find(key);
      const_iterator l = f;

      if (l != end())
      {
        ++l;
        ++n;

        while ((l != end()) && key_equal_function(key, *l))
        {
          ++l;
          ++n;
        }
      }

      return n;
    }

    //*********************************************************************
    /// Finds an element.
    ///\param key The key to search for.
    ///\return An iterator to the element if the key exists, otherwise end().
    //*********************************************************************
    iterator find(key_parameter_t key)
    {
      size_t index = get_bucket_index(key);

      bucket_t* pbucket = pbuckets + index;
      bucket_t& bucket = *pbucket;

      // Is the bucket not empty?
      if (!bucket.empty())
      {
        // Step though the list until we find the end or an equivalent key.
        local_iterator inode = bucket.begin();
        local_iterator iend = bucket.end();

        while (inode != iend)
        {
          // Do we have this one?
          if (key_equal_function(key, inode->key))
          {
            return iterator((pbuckets + number_of_buckets), pbucket, inode);
          }

          ++inode;
        }
      }

      return end();
    }

    //*********************************************************************
    /// Finds an element.
    ///\param key The key to search for.
    ///\return An iterator to the element if the key exists, otherwise end().
    //*********************************************************************
    const_iterator find(key_parameter_t key) const
    {
      size_t index = get_bucket_index(key);

      bucket_t* pbucket = pbuckets + index;
      bucket_t& bucket = *pbucket;

      // Is the bucket not empty?
      if (!bucket.empty())
      {
        // Step though the list until we find the end or an equivalent key.
        local_iterator inode = bucket.begin();
        local_iterator iend = bucket.end();

        while (inode != iend)
        {
          // Do we have this one?
          if (key_equal_function(key, inode->key))
          {
            return iterator((pbuckets + number_of_buckets), pbucket, inode);
          }

          ++inode;
        }
      }

      return end();
    }

    //*********************************************************************
    /// Returns a range containing all elements with key key in the container.
    /// The range is defined by two iterators, the first pointing to the first
    /// element of the wanted range and the second pointing past the last
    /// element of the range.
    ///\param key The key to search for.
    ///\return An iterator pair to the range of elements if the key exists, otherwise end().
    //*********************************************************************
    ETL_OR_STD::pair<iterator, iterator> equal_range(key_parameter_t key)
    {
      iterator f = find(key);
      iterator l = f;

      if (l != end())
      {
        ++l;

        while ((l != end()) && key_equal_function(key, *l))
        {
          ++l;
        }
      }

      return ETL_OR_STD::pair<iterator, iterator>(f, l);
    }

    //*********************************************************************
    /// Returns a range containing all elements with key key in the container.
    /// The range is defined by two iterators, the first pointing to the first
    /// element of the wanted range and the second pointing past the last
    /// element of the range.
    ///\param key The key to search for.
    ///\return A const iterator pair to the range of elements if the key exists, otherwise end().
    //*********************************************************************
    ETL_OR_STD::pair<const_iterator, const_iterator> equal_range(key_parameter_t key) const
    {
      const_iterator f = find(key);
      const_iterator l = f;

      if (l != end())
      {
        ++l;

        while ((l != end()) && key_equal_function(key, *l))
        {
          ++l;
        }
      }

      return ETL_OR_STD::pair<const_iterator, const_iterator>(f, l);
    }

    //*************************************************************************
    /// Gets the size of the unordered_multiset.
    //*************************************************************************
    size_type size() const
    {
      return pnodepool->size();
    }

    //*************************************************************************
    /// Gets the maximum possible size of the unordered_multiset.
    //*************************************************************************
    size_type max_size() const
    {
      return pnodepool->max_size();
    }

    //*************************************************************************
    /// Gets the maximum possible size of the unordered_multiset.
    //*************************************************************************
    size_type capacity() const
    {
      return pnodepool->max_size();
    }

    //*************************************************************************
    /// Checks to see if the unordered_multiset is empty.
    //*************************************************************************
    bool empty() const
    {
      return pnodepool->empty();
    }

    //*************************************************************************
    /// Checks to see if the unordered_multiset is full.
    //*************************************************************************
    bool full() const
    {
      return pnodepool->full();
    }

    //*************************************************************************
    /// Returns the remaining capacity.
    ///\return The remaining capacity.
    //*************************************************************************
    size_t available() const
    {
      return pnodepool->available();
    }

    //*************************************************************************
    /// Returns the load factor = size / bucket_count.
    ///\return The load factor = size / bucket_count.
    //*************************************************************************
    float load_factor() const
    {
      return static_cast<float>(size()) / static_cast<float>(bucket_count());
    }

    //*************************************************************************
    /// Returns the function that hashes the keys.
    ///\return The function that hashes the keys..
    //*************************************************************************
    hasher hash_function() const
    {
      return key_hash_function;
    }

    //*************************************************************************
    /// Returns the function that compares the keys.
    ///\return The function that compares the keys..
    //*************************************************************************
    key_equal key_eq() const
    {
      return key_equal_function;
    }

    //*************************************************************************
    /// Assignment operator.
    //*************************************************************************
    iunordered_multiset& operator = (const iunordered_multiset& rhs)
    {
      // Skip if doing self assignment
      if (this != &rhs)
      {
        key_hash_function  = rhs.hash_function();
        key_equal_function = rhs.key_eq();
        assign(rhs.cbegin(), rhs.cend());
      }

      return *this;
    }

#if ETL_USING_CPP11
    //*************************************************************************
    /// Assignment operator.
    //*************************************************************************
    iunordered_multiset& operator = (iunordered_multiset&& rhs)
    {
      // Skip if doing self assignment
      if (this != &rhs)
      {
        clear();
        key_hash_function  = rhs.hash_function();
        key_equal_function = rhs.key_eq();
        move(rhs.begin(), rhs.end());
      }

      return *this;
    }
#endif

  protected:

    //*********************************************************************
    /// Constructor.
    //*********************************************************************
    iunordered_multiset(pool_t& node_pool_, bucket_t* pbuckets_, size_t number_of_buckets_, hasher key_hash_function_, key_equal key_equal_function_)
      : pnodepool(&node_pool_)
      , pbuckets(pbuckets_)
      , number_of_buckets(number_of_buckets_)
      , first(pbuckets)
      , last(pbuckets)
      , key_hash_function(key_hash_function_)
      , key_equal_function(key_equal_function_)
    {
    }

    //*********************************************************************
    /// Initialise the unordered_multiset.
    //*********************************************************************
    void initialise()
    {
      if (!empty())
      {
        // For each bucket...
        for (size_t i = 0UL; i < number_of_buckets; ++i)
        {
          bucket_t& bucket = pbuckets[i];

          if (!bucket.empty())
          {
            // For each item in the bucket...
            local_iterator it = bucket.begin();

            while (it != bucket.end())
            {
              // Destroy the value contents.
              it->key.~value_type();
              ++it;
              ETL_DECREMENT_DEBUG_COUNT;
            }

            // Now it's safe to clear the bucket.
            bucket.clear();
          }
        }

        // Now it's safe to clear the entire pool in one go.
        pnodepool->release_all();
      }

      first = pbuckets;
      last  = first;
    }

#if ETL_USING_CPP11
    //*************************************************************************
    /// Move from a range
    //*************************************************************************
    void move(iterator b, iterator e)
    {
      while (b != e)
      {
        iterator temp = b;
        ++temp;
        insert(etl::move(*b));
        b = temp;
      }
    }
#endif

  private:

    //*************************************************************************
    /// Create a node.
    //*************************************************************************
    node_t* allocate_data_node()
    {
      node_t* (etl::ipool::*func)() = &etl::ipool::allocate<node_t>;
      return (pnodepool->*func)();
    }

    //*********************************************************************
    /// Adjust the first and last markers according to the new entry.
    //*********************************************************************
    void adjust_first_last_markers_after_insert(bucket_t* pbucket)
    {
      if (size() == 1)
      {
        first = pbucket;
        last  = pbucket;
      }
      else
      {
        if (pbucket < first)
        {
          first = pbucket;
        }
        else if (pbucket > last)
        {
          last = pbucket;
        }
      }
    }

    //*********************************************************************
    /// Adjust the first and last markers according to the erased entry.
    //*********************************************************************
    void adjust_first_last_markers_after_erase(bucket_t* pbucket)
    {
      if (empty())
      {
        first = pbuckets;
        last  = pbuckets;
      }
      else
      {
        if (pbucket == first)
        {
          // We erased the first so, we need to search again from where we erased.
          while (first->empty())
          {
            ++first;
          }
        }
        else if (pbucket == last)
        {
          // We erased the last, so we need to search again. Start from the first, go no further than the current last.
          pbucket = first;
          bucket_t* pend = last;

          last = first;

          while (pbucket != pend)
          {
            if (!pbucket->empty())
            {
              last = pbucket;
            }

            ++pbucket;
          }
        }
      }
    }

    //*********************************************************************
    /// Delete a data node at the specified location.
    //*********************************************************************
    local_iterator delete_data_node(local_iterator iprevious, local_iterator icurrent, bucket_t& bucket)
    {
      local_iterator inext = bucket.erase_after(iprevious); // Unlink from the bucket.
      icurrent->key.~value_type();                          // Destroy the value.
      pnodepool->release(&*icurrent);                       // Release it back to the pool.
      adjust_first_last_markers_after_erase(&bucket);
      ETL_DECREMENT_DEBUG_COUNT;

      return inext;
    }

    // Disable copy construction.
    iunordered_multiset(const iunordered_multiset&);

    /// The pool of data nodes used in the list.
    pool_t* pnodepool;

    /// The bucket list.
    bucket_t* pbuckets;

    /// The number of buckets.
    const size_t number_of_buckets;

    /// The first and last iterators to buckets with values.
    bucket_t* first;
    bucket_t* last;

    /// The function that creates the hashes.
    hasher key_hash_function;

    /// The function that compares the keys for equality.
    key_equal key_equal_function;

    /// For library debugging purposes only.
    ETL_DECLARE_DEBUG_COUNT;

    //*************************************************************************
    /// Destructor.
    //*************************************************************************
#if defined(ETL_POLYMORPHIC_UNORDERED_MULTISET) || defined(ETL_POLYMORPHIC_CONTAINERS)
  public:
    virtual ~iunordered_multiset()
    {
    }
#else
  protected:
    ~iunordered_multiset()
    {
    }
#endif
  };

  //***************************************************************************
  /// Equal operator.
  ///\param lhs Reference to the first unordered_multiset.
  ///\param rhs Reference to the second unordered_multiset.
  ///\return <b>true</b> if the arrays are equal, otherwise <b>false</b>
  ///\ingroup unordered_multiset
  //***************************************************************************
  template <typename TKey, typename THash, typename TKeyEqual>
  bool operator ==(const etl::iunordered_multiset<TKey, THash, TKeyEqual>& lhs, 
                   const etl::iunordered_multiset<TKey, THash, TKeyEqual>& rhs)
  {
    const bool sizes_match = (lhs.size() == rhs.size());
    bool elements_match = true;

    typedef typename etl::iunordered_multiset<TKey, THash, TKeyEqual>::const_iterator itr_t;

    if (sizes_match)
    {
      itr_t l_begin = lhs.begin();
      itr_t l_end   = lhs.end();

      while ((l_begin != l_end) && elements_match)
      {
        const TKey l_value = *l_begin;

        // See if the lhs keys exist in the rhs.
        ETL_OR_STD::pair<itr_t, itr_t> l_range = lhs.equal_range(l_value);
        ETL_OR_STD::pair<itr_t, itr_t> r_range = rhs.equal_range(l_value);

        if (r_range.first != rhs.end())
        {
          bool distance_match = (etl::distance(l_range.first, l_range.second) == etl::distance(r_range.first, r_range.second));

          if (distance_match)
          {
            elements_match = etl::is_permutation(l_range.first, l_range.second, r_range.first, r_range.second);
          }
          else
          {
            elements_match = false;
          }
        }
        else
        {
          elements_match = false;
        }

        ++l_begin;
      }
    }

    return (sizes_match && elements_match);
  }

  //***************************************************************************
  /// Not equal operator.
  ///\param lhs Reference to the first unordered_multiset.
  ///\param rhs Reference to the second unordered_multiset.
  ///\return <b>true</b> if the arrays are not equal, otherwise <b>false</b>
  ///\ingroup unordered_multiset
  //***************************************************************************
  template <typename TKey, typename THash, typename TKeyEqual>
  bool operator !=(const etl::iunordered_multiset<TKey, THash, TKeyEqual>& lhs, 
                   const etl::iunordered_multiset<TKey, THash, TKeyEqual>& rhs)
  {
    return !(lhs == rhs);
  }

  //*************************************************************************
  /// A templated unordered_multiset implementation that uses a fixed size buffer.
  //*************************************************************************
  template <typename TKey, const size_t MAX_SIZE_, size_t MAX_BUCKETS_ = MAX_SIZE_, typename THash = etl::hash<TKey>, typename TKeyEqual = etl::equal_to<TKey> >
  class unordered_multiset : public etl::iunordered_multiset<TKey, THash, TKeyEqual>
  {
  private:

    typedef etl::iunordered_multiset<TKey, THash, TKeyEqual> base;

  public:

    static ETL_CONSTANT size_t MAX_SIZE    = MAX_SIZE_;
    static ETL_CONSTANT size_t MAX_BUCKETS = MAX_BUCKETS_;


    //*************************************************************************
    /// Default constructor.
    //*************************************************************************
    unordered_multiset(const THash& hash = THash(), const TKeyEqual& equal = TKeyEqual())
      : base(node_pool, buckets, MAX_BUCKETS, hash, equal)
    {
    }

    //*************************************************************************
    /// Copy constructor.
    //*************************************************************************
    unordered_multiset(const unordered_multiset& other)
      : base(node_pool, buckets, MAX_BUCKETS, other.hash_function(), other.key_eq())
    {
      // Skip if doing self assignment
      if (this != &other)
      {
        base::assign(other.cbegin(), other.cend());
      }
    }


#if ETL_USING_CPP11
    //*************************************************************************
    /// Move constructor.
    //*************************************************************************
    unordered_multiset(unordered_multiset&& other)
      : base(node_pool, buckets, MAX_BUCKETS, other.hash_function(), other.key_eq())
    {
      // Skip if doing self assignment
      if (this != &other)
      {
        base::move(other.begin(), other.end());
      }
    }
#endif

    //*************************************************************************
    /// Constructor, from an iterator range.
    ///\tparam TIterator The iterator type.
    ///\param first The iterator to the first element.
    ///\param last  The iterator to the last element + 1.
    //*************************************************************************
    template <typename TIterator>
    unordered_multiset(TIterator first_, TIterator last_, const THash& hash = THash(), const TKeyEqual& equal = TKeyEqual())
      : base(node_pool, buckets, MAX_BUCKETS, hash, equal)
    {
      base::assign(first_, last_);
    }

#if ETL_HAS_INITIALIZER_LIST
    //*************************************************************************
    /// Construct from initializer_list.
    //*************************************************************************
    unordered_multiset(std::initializer_list<TKey> init, const THash& hash = THash(), const TKeyEqual& equal = TKeyEqual())
      : base(node_pool, buckets, MAX_BUCKETS, hash, equal)
    {
      base::assign(init.begin(), init.end());
    }
#endif

    //*************************************************************************
    /// Destructor.
    //*************************************************************************
    ~unordered_multiset()
    {
      base::initialise();
    }

    //*************************************************************************
    /// Assignment operator.
    //*************************************************************************
    unordered_multiset& operator = (const unordered_multiset& rhs)
    {
      base::operator =(rhs);

      return *this;
    }

#if ETL_USING_CPP11
    //*************************************************************************
    /// Move assignment operator.
    //*************************************************************************
    unordered_multiset& operator = (unordered_multiset&& rhs)
    {
      base::operator =(etl::move(rhs));

      return *this;
    }
#endif

  private:

    /// The pool of nodes used for the unordered_multiset.
    etl::pool<typename base::node_t, MAX_SIZE> node_pool;

    /// The buckets of node lists.
    typename base::bucket_t buckets[MAX_BUCKETS_];
  };

  //*************************************************************************
  /// Template deduction guides.
  //*************************************************************************
#if ETL_USING_CPP17 && ETL_HAS_INITIALIZER_LIST
  template <typename... T>
  unordered_multiset(T...) -> unordered_multiset<etl::nth_type_t<0, T...>, sizeof...(T)>;
#endif

  //*************************************************************************
  /// Make
  //*************************************************************************
#if ETL_USING_CPP11 && ETL_HAS_INITIALIZER_LIST
  template <typename TKey, typename THash = etl::hash<TKey>, typename TKeyEqual = etl::equal_to<TKey>, typename... T>
  constexpr auto make_unordered_multiset(T&&... keys) -> etl::unordered_multiset<TKey, sizeof...(T), sizeof...(T), THash, TKeyEqual>
  {
    return { etl::forward<T>(keys)... };
  }
#endif
}

#endif