hashtable

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// Internal header for TR1 unordered_set and unordered_map -*- C++ -*-

// Copyright (C) 2005 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 2, 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.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

/** @file 
 *  This is a TR1 C++ Library header. 
 */

// This header file defines std::tr1::hashtable, which is used to
// implement std::tr1::unordered_set, std::tr1::unordered_map, 
// std::tr1::unordered_multiset, and std::tr1::unordered_multimap.
// hashtable has many template parameters, partly to accommodate
// the differences between those four classes and partly to 
// accommodate policy choices that go beyond what TR1 calls for.

// ??? Arguably this should be Internal::hashtable, not std::tr1::hashtable.

// Class template hashtable attempts to encapsulate all reasonable
// variation among hash tables that use chaining.  It does not handle
// open addressing.

// References: 
// M. Austern, "A Proposal to Add Hash Tables to the Standard
//    Library (revision 4)," WG21 Document N1456=03-0039, 2003.
// D. E. Knuth, The Art of Computer Programming, v. 3, Sorting and Searching.
// A. Tavori and V. Dreizin, "Generic Associative Containers", 2004.
//    ??? Full citation?

#ifndef GNU_LIBSTDCXX_TR1_HASHTABLE_
#define GNU_LIBSTDCXX_TR1_HASHTABLE_

#include <utility>		// For std::pair
#include <iterator>
#include <cstddef>
#include <cstdlib>
#include <cmath>
#include <bits/functexcept.h>
#include <tr1/type_traits>	// For true_type and false_type

//----------------------------------------------------------------------
// General utilities

namespace Internal
{
  template<bool Flag, typename IfTrue, typename IfFalse>
    struct IF;

  template<typename IfTrue, typename IfFalse>
    struct IF<true, IfTrue, IfFalse>
    { typedef IfTrue type; };
 
  template <typename IfTrue, typename IfFalse>
    struct IF<false, IfTrue, IfFalse>
    { typedef IfFalse type; };

  // Helper function: return distance(first, last) for forward
  // iterators, or 0 for input iterators.
  template<class Iterator>
    inline typename std::iterator_traits<Iterator>::difference_type
    distance_fw(Iterator first, Iterator last, std::input_iterator_tag)
    { return 0; }

  template<class Iterator>
    inline typename std::iterator_traits<Iterator>::difference_type
    distance_fw(Iterator first, Iterator last, std::forward_iterator_tag)
    { return std::distance(first, last); }

  template<class Iterator>
    inline typename std::iterator_traits<Iterator>::difference_type
    distance_fw(Iterator first, Iterator last)
    {
      typedef typename std::iterator_traits<Iterator>::iterator_category tag;
      return distance_fw(first, last, tag());
    }
  
} // namespace Internal

//----------------------------------------------------------------------
// Auxiliary types used for all instantiations of hashtable: nodes
// and iterators.

// Nodes, used to wrap elements stored in the hash table.  A policy
// template parameter of class template hashtable controls whether
// nodes also store a hash code. In some cases (e.g. strings) this may
// be a performance win.

namespace Internal
{
  template<typename Value, bool cache_hash_code>
    struct hash_node;

  template<typename Value>
    struct hash_node<Value, true>
    {
      Value m_v;
      std::size_t hash_code;
      hash_node* m_next;
    };

  template<typename Value>
    struct hash_node<Value, false>
    {
      Value m_v;
      hash_node* m_next;
    };

  // Local iterators, used to iterate within a bucket but not between
  // buckets.

  template<typename Value, bool cache>
    struct node_iterator_base
    {
      node_iterator_base(hash_node<Value, cache>* p)
      : m_cur(p) { }
      
      void
      incr()
      { m_cur = m_cur->m_next; }

      hash_node<Value, cache>* m_cur;
    };

  template<typename Value, bool cache>
    inline bool
    operator==(const node_iterator_base<Value, cache>& x,
	       const node_iterator_base<Value, cache>& y)
    { return x.m_cur == y.m_cur; }

  template<typename Value, bool cache>
    inline bool
    operator!=(const node_iterator_base<Value, cache>& x,
	       const node_iterator_base<Value, cache>& y)
    { return x.m_cur != y.m_cur; }

  template<typename Value, bool constant_iterators, bool cache>
    struct node_iterator
    : public node_iterator_base<Value, cache>
    {
      typedef Value                                    value_type;
      typedef typename IF<constant_iterators, const Value*, Value*>::type
                                                       pointer;
      typedef typename IF<constant_iterators, const Value&, Value&>::type
                                                       reference;
      typedef std::ptrdiff_t                           difference_type;
      typedef std::forward_iterator_tag                iterator_category;

      explicit
      node_iterator(hash_node<Value, cache>* p = 0)
      : node_iterator_base<Value, cache>(p) { }

      reference
      operator*() const
      { return this->m_cur->m_v; }
  
      pointer
      operator->() const
      { return &this->m_cur->m_v; }

      node_iterator&
      operator++()
      { 
	this->incr(); 
	return *this; 
      }
  
      node_iterator
      operator++(int)
      { 
	node_iterator tmp(*this);
	this->incr();
	return tmp;
      }
    };

  template<typename Value, bool constant_iterators, bool cache>
    struct node_const_iterator
    : public node_iterator_base<Value, cache>
    {
      typedef Value                                    value_type;
      typedef const Value*                             pointer;
      typedef const Value&                             reference;
      typedef std::ptrdiff_t                           difference_type;
      typedef std::forward_iterator_tag                iterator_category;

      explicit
      node_const_iterator(hash_node<Value, cache>* p = 0)
      : node_iterator_base<Value, cache>(p) { }

      node_const_iterator(const node_iterator<Value, constant_iterators,
			  cache>& x)
      : node_iterator_base<Value, cache>(x.m_cur) { }

      reference
      operator*() const
      { return this->m_cur->m_v; }
  
      pointer
      operator->() const
      { return &this->m_cur->m_v; }

      node_const_iterator&
      operator++()
      { 
	this->incr(); 
	return *this; 
      }
  
      node_const_iterator
      operator++(int)
      { 
	node_const_iterator tmp(*this);
	this->incr();
	return tmp;
      }
    };

  template<typename Value, bool cache>
    struct hashtable_iterator_base
    {
      hashtable_iterator_base(hash_node<Value, cache>* node,
			      hash_node<Value, cache>** bucket)
      : m_cur_node(node), m_cur_bucket(bucket)
      { }

      void
      incr()
      {
	m_cur_node = m_cur_node->m_next;
	if (!m_cur_node)
	  m_incr_bucket();
      }

      void
      m_incr_bucket();

      hash_node<Value, cache>* m_cur_node;
      hash_node<Value, cache>** m_cur_bucket;
    };

  // Global iterators, used for arbitrary iteration within a hash
  // table.  Larger and more expensive than local iterators.
  template<typename Value, bool cache>
    void
    hashtable_iterator_base<Value, cache>::
    m_incr_bucket()
    {
      ++m_cur_bucket;

      // This loop requires the bucket array to have a non-null sentinel.
      while (!*m_cur_bucket)
	++m_cur_bucket;
      m_cur_node = *m_cur_bucket;
    }

  template<typename Value, bool cache>
    inline bool
    operator==(const hashtable_iterator_base<Value, cache>& x,
	       const hashtable_iterator_base<Value, cache>& y)
    { return x.m_cur_node == y.m_cur_node; }

  template<typename Value, bool cache>
    inline bool
    operator!=(const hashtable_iterator_base<Value, cache>& x,
	       const hashtable_iterator_base<Value, cache>& y)
    { return x.m_cur_node != y.m_cur_node; }

  template<typename Value, bool constant_iterators, bool cache>
    struct hashtable_iterator
    : public hashtable_iterator_base<Value, cache>
    {
      typedef Value                                    value_type;
      typedef typename IF<constant_iterators, const Value*, Value*>::type
                                                       pointer;
      typedef typename IF<constant_iterators, const Value&, Value&>::type
                                                       reference;
      typedef std::ptrdiff_t                           difference_type;
      typedef std::forward_iterator_tag                iterator_category;

      hashtable_iterator(hash_node<Value, cache>* p,
			 hash_node<Value, cache>** b)
      : hashtable_iterator_base<Value, cache>(p, b) { }

      explicit
      hashtable_iterator(hash_node<Value, cache>** b)
      : hashtable_iterator_base<Value, cache>(*b, b) { }
  
      reference
      operator*() const
      { return this->m_cur_node->m_v; }
  
      pointer
      operator->() const
      { return &this->m_cur_node->m_v; }

      hashtable_iterator&
      operator++()
      { 
	this->incr();
	return *this;
      }
  
      hashtable_iterator
      operator++(int)
      { 
	hashtable_iterator tmp(*this);
	this->incr();
	return tmp;
      }
    };

  template<typename Value, bool constant_iterators, bool cache>
    struct hashtable_const_iterator
    : public hashtable_iterator_base<Value, cache>
    {
      typedef Value                                    value_type;
      typedef const Value*                             pointer;
      typedef const Value&                             reference;
      typedef std::ptrdiff_t                           difference_type;
      typedef std::forward_iterator_tag                iterator_category;

      hashtable_const_iterator(hash_node<Value, cache>* p,
			       hash_node<Value, cache>** b)
      : hashtable_iterator_base<Value, cache>(p, b) { }

      explicit
      hashtable_const_iterator(hash_node<Value, cache>** b)
      : hashtable_iterator_base<Value, cache>(*b, b) { }
  
      hashtable_const_iterator(const hashtable_iterator<Value,
			       constant_iterators, cache>& x)
      : hashtable_iterator_base<Value, cache>(x.m_cur_node, x.m_cur_bucket) { }

      reference
      operator*() const
      { return this->m_cur_node->m_v; }
  
      pointer
      operator->() const
      { return &this->m_cur_node->m_v; }

      hashtable_const_iterator&
      operator++()
      { 
	this->incr();
	return *this;
      }
  
      hashtable_const_iterator
      operator++(int)
      { 
	hashtable_const_iterator tmp(*this);
	this->incr();
	return tmp;
      }
    };
} // namespace Internal

// ----------------------------------------------------------------------
// Many of class template hashtable's template parameters are policy
// classes.  These are defaults for the policies.

namespace Internal
{
  // The two key extraction policies used by the *set and *map variants.
  template<typename T>
    struct identity
    {
      T
      operator()(const T& t) const
      { return t; }
    };

  template<typename Pair>
    struct extract1st
    {
      typename Pair::first_type
      operator()(const Pair& p) const
      { return p.first; }
    };

  // Default range hashing function: use division to fold a large number
  // into the range [0, N).
  struct mod_range_hashing
  {
    typedef std::size_t first_argument_type;
    typedef std::size_t second_argument_type;
    typedef std::size_t result_type;

    result_type
    operator() (first_argument_type r, second_argument_type N) const
    { return r % N; }
  };

  // Default ranged hash function H.  In principle it should be a
  // function object composed from objects of type H1 and H2 such that
  // h(k, N) = h2(h1(k), N), but that would mean making extra copies of
  // h1 and h2.  So instead we'll just use a tag to tell class template
  // hashtable to do that composition.
  struct default_ranged_hash { };

  // Default value for rehash policy.  Bucket size is (usually) the
  // smallest prime that keeps the load factor small enough.
  struct prime_rehash_policy
  {
    prime_rehash_policy(float z = 1.0);
    
    float
    max_load_factor() const;

    // Return a bucket size no smaller than n.
    std::size_t
    next_bkt(std::size_t n) const;
    
    // Return a bucket count appropriate for n elements
    std::size_t
    bkt_for_elements(std::size_t n) const;
    
    // n_bkt is current bucket count, n_elt is current element count,
    // and n_ins is number of elements to be inserted.  Do we need to
    // increase bucket count?  If so, return make_pair(true, n), where n
    // is the new bucket count.  If not, return make_pair(false, 0).
    std::pair<bool, std::size_t>
    need_rehash(std::size_t n_bkt, std::size_t n_elt, std::size_t n_ins) const;
    
    float m_max_load_factor;
    float m_growth_factor;
    mutable std::size_t m_next_resize;
  };

  // XXX This is a hack.  prime_rehash_policy's member functions, and
  // certainly the list of primes, should be defined in a .cc file.
  // We're temporarily putting them in a header because we don't have a
  // place to put TR1 .cc files yet.  There's no good reason for any of
  // prime_rehash_policy's member functions to be inline, and there's
  // certainly no good reason for X<> to exist at all.
  
  struct lt
  {
    template<typename X, typename Y>
      bool
      operator()(X x, Y y)
      { return x < y; }
  };