STL之hashtable源代码剖析

Posted 2020-10-02 brucemengbm

// Filename:    stl_hashtable.h

////////////////////////////////////////////////////////////////////////////////
// 本实作的hashtable採用的是开链法, 其内存布局例如以下
////////////////////////////////////////////////////////////////////////////////
// 对于产生哈希冲突的结点, 我们採取在其位置维护一个链表才处理之
//
//  ------------------------------------------------------------------------
//  |      |      |      |      |      | ..... |      |      |      |      |
//  ------------------------------------------------------------------------
//      |             |                                   |
//      ↓             ↓                                   ↓
//  --------       --------  --------  --------        --------
//  | next |->0    | next |->| next |->| next |->0     | next |->0
//  --------       --------  --------  --------        --------
//  | data |       | data |  | data |  | data |        | data |
//  --------       --------  --------  --------        --------
////////////////////////////////////////////////////////////////////////////////

/*
 * Copyright (c) 1996,1997
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 */

/* NOTE: This is an internal header file, included by other STL headers.
 *   You should not attempt to use it directly.
 */

#ifndef __SGI_STL_INTERNAL_HASHTABLE_H
#define __SGI_STL_INTERNAL_HASHTABLE_H

// hashtable类用于实现哈希关联容器hash_set, hash_map, hash_multiset和hash_multimap

#include <stl_algobase.h>
#include <stl_alloc.h>
#include <stl_construct.h>
#include <stl_tempbuf.h>
#include <stl_algo.h>
#include <stl_uninitialized.h>
#include <stl_function.h>
#include <stl_vector.h>
#include <stl_hash_fun.h>

__STL_BEGIN_NAMESPACE

// 这个是哈希表中维护的链表结点
template <class Value>
struct __hashtable_node
{
  __hashtable_node* next;
  Value val;
};

// 这里使用前置声明, 否则后面的交叉引用会导致编译错误
template <class Value, class Key, class HashFcn,
          class ExtractKey, class EqualKey, class Alloc = alloc>
class hashtable;

template <class Value, class Key, class HashFcn,
          class ExtractKey, class EqualKey, class Alloc>
struct __hashtable_iterator;

template <class Value, class Key, class HashFcn,
          class ExtractKey, class EqualKey, class Alloc>
struct __hashtable_const_iterator;

template <class Value, class Key, class HashFcn,
          class ExtractKey, class EqualKey, class Alloc>
struct __hashtable_iterator
{
  // 注意: hashtable不提供reverse iterator, 也不提供operator --
  typedef hashtable<Value, Key, HashFcn, ExtractKey, EqualKey, Alloc>
          hashtable;
  typedef __hashtable_iterator<Value, Key, HashFcn,
                               ExtractKey, EqualKey, Alloc>
          iterator;
  typedef __hashtable_const_iterator<Value, Key, HashFcn,
                                     ExtractKey, EqualKey, Alloc>
          const_iterator;
  typedef __hashtable_node<Value> node;

  typedef forward_iterator_tag iterator_category;
  typedef Value value_type;
  typedef ptrdiff_t difference_type;
  typedef size_t size_type;
  typedef Value& reference;
  typedef Value* pointer;

  // 本实作中hasntable是由一个线性表作为hash表, 而表内的每个被映射的
  // 哈希结点内部维护这一个链表, 用于处理哈希冲突, 此即开链法
  node* cur;            // 当前的位置, 是线性表中的链表结点
  hashtable* ht;        // 线性表中的位置

  __hashtable_iterator(node* n, hashtable* tab) : cur(n), ht(tab) {}
  __hashtable_iterator() {}

  reference operator*() const { return cur->val; }

#ifndef __SGI_STL_NO_ARROW_OPERATOR
  // 假设编译器支持'->'则重载, 具体见我在<stl_list.h>中的剖析
  pointer operator->() const { return &(operator*()); }
#endif /* __SGI_STL_NO_ARROW_OPERATOR */

  // 具体解析见实现部分
  iterator& operator++();
  iterator operator++(int);

  bool operator==(const iterator& it) const { return cur == it.cur; }
  bool operator!=(const iterator& it) const { return cur != it.cur; }
};

// const情况基本和上面一致
template <class Value, class Key, class HashFcn,
          class ExtractKey, class EqualKey, class Alloc>
struct __hashtable_const_iterator
{
  typedef hashtable<Value, Key, HashFcn, ExtractKey, EqualKey, Alloc>
          hashtable;
  typedef __hashtable_iterator<Value, Key, HashFcn,
                               ExtractKey, EqualKey, Alloc>
          iterator;
  typedef __hashtable_const_iterator<Value, Key, HashFcn,
                                     ExtractKey, EqualKey, Alloc>
          const_iterator;
  typedef __hashtable_node<Value> node;

  typedef forward_iterator_tag iterator_category;
  typedef Value value_type;
  typedef ptrdiff_t difference_type;
  typedef size_t size_type;
  typedef const Value& reference;
  typedef const Value* pointer;

  const node* cur;
  const hashtable* ht;

  __hashtable_const_iterator(const node* n, const hashtable* tab)
    : cur(n), ht(tab) {}
  __hashtable_const_iterator() {}
  __hashtable_const_iterator(const iterator& it) : cur(it.cur), ht(it.ht) {}
  reference operator*() const { return cur->val; }
#ifndef __SGI_STL_NO_ARROW_OPERATOR
  pointer operator->() const { return &(operator*()); }
#endif /* __SGI_STL_NO_ARROW_OPERATOR */
  const_iterator& operator++();
  const_iterator operator++(int);
  bool operator==(const const_iterator& it) const { return cur == it.cur; }
  bool operator!=(const const_iterator& it) const { return cur != it.cur; }
};

// 假设long至少为32-bits, 否则依据情况自己改动
static const int __stl_num_primes = 28;
static const unsigned long __stl_prime_list[__stl_num_primes] =
{
  53,         97,           193,         389,       769,
  1543,       3079,         6151,        12289,     24593,
  49157,      98317,        196613,      393241,    786433,
  1572869,    3145739,      6291469,     12582917,  25165843,
  50331653,   100663319,    201326611,   402653189, 805306457,
  1610612741, 3221225473ul, 4294967291ul
};

// 返回大于n的最小素数
inline unsigned long __stl_next_prime(unsigned long n)
{
  const unsigned long* first = __stl_prime_list;
  const unsigned long* last = __stl_prime_list + __stl_num_primes;
  const unsigned long* pos = lower_bound(first, last, n);
  return pos == last ?
 *(last - 1) : *pos;
}

// Value:       结点的valule类型
// Key:         结点的key类型
// HashFcn:     hash function
// ExtractKey:  从结点中取出键值的方法
// EqualKey:    推断键值是否同样的方法
// Alloc:       allocator, 默认alloc
template <class Value, class Key, class HashFcn,
          class ExtractKey, class EqualKey,
          class Alloc>
class hashtable
{
public:
  typedef Key key_type;
  typedef Value value_type;
  typedef HashFcn hasher;
  typedef EqualKey key_equal;

  typedef size_t            size_type;
  typedef ptrdiff_t         difference_type;
  typedef value_type*       pointer;
  typedef const value_type* const_pointer;
  typedef value_type&       reference;
  typedef const value_type& const_reference;

  // 获取hash相关的函数
  hasher hash_funct() const { return hash; }
  key_equal key_eq() const { return equals; }

private:
  // 具体剖析參考<stl_fun_fun.h>
  hasher hash;
  key_equal equals;
  ExtractKey get_key;

  typedef __hashtable_node<Value> node;
  typedef simple_alloc<node, Alloc> node_allocator;

  vector<node*,Alloc> buckets;  // 线性表以vector实作
  size_type num_elements;

public:
  typedef __hashtable_iterator<Value, Key, HashFcn, ExtractKey, EqualKey,
                               Alloc>
  iterator;

  typedef __hashtable_const_iterator<Value, Key, HashFcn, ExtractKey, EqualKey,
                                     Alloc>
  const_iterator;

  friend struct
  __hashtable_iterator<Value, Key, HashFcn, ExtractKey, EqualKey, Alloc>;
  friend struct
  __hashtable_const_iterator<Value, Key, HashFcn, ExtractKey, EqualKey, Alloc>;

public:
  // 以下这些函数STL容器的表现基本一致,
  // 不做说明, 能够參看<stl_vector.h>, <stl_list.h>中的解析
  hashtable(size_type n,
            const HashFcn&    hf,
            const EqualKey&   eql,
            const ExtractKey& ext)
    : hash(hf), equals(eql), get_key(ext), num_elements(0)
  {
    initialize_buckets(n);
  }

  hashtable(size_type n,
            const HashFcn&    hf,
            const EqualKey&   eql)
    : hash(hf), equals(eql), get_key(ExtractKey()), num_elements(0)
  {
    initialize_buckets(n);
  }

  hashtable(const hashtable& ht)
    : hash(ht.hash), equals(ht.equals), get_key(ht.get_key), num_elements(0)
  {
    copy_from(ht);
  }

  hashtable& operator= (const hashtable& ht)
  {
    if (&ht != this) {
      clear();
      hash = ht.hash;
      equals = ht.equals;
      get_key = ht.get_key;
      copy_from(ht);
    }
    return *this;
  }

  ~hashtable() { clear(); }

  size_type size() const { return num_elements; }
  size_type max_size() const { return size_type(-1); }
  bool empty() const { return size() == 0; }

  void swap(hashtable& ht)
  {
    __STD::swap(hash, ht.hash);
    __STD::swap(equals, ht.equals);
    __STD::swap(get_key, ht.get_key);
    buckets.swap(ht.buckets);
    __STD::swap(num_elements, ht.num_elements);
  }

  iterator begin()
  {
    for (size_type n = 0; n < buckets.size(); ++n)
      if (buckets[n])
        return iterator(buckets[n], this);
    return end();
  }

  iterator end() { return iterator(0, this); }

  const_iterator begin() const
  {
    for (size_type n = 0; n < buckets.size(); ++n)
      if (buckets[n])
        return const_iterator(buckets[n], this);
    return end();
  }

  const_iterator end() const { return const_iterator(0, this); }

  friend bool
  operator== __STL_NULL_TMPL_ARGS (const hashtable&, const hashtable&);

public:
  // 线性表中的结点数
  size_type bucket_count() const { return buckets.size(); }

  // 线性表最多能分配的结点数
  size_type max_bucket_count() const
    { return __stl_prime_list[__stl_num_primes - 1]; }

  // 返回指定key映射了多少value
  size_type elems_in_bucket(size_type bucket) const
  {
    size_type result = 0;
    for (node* cur = buckets[bucket]; cur; cur = cur->next)
      result += 1;
    return result;
  }

  // 插入操作, 不同意反复
  pair<iterator, bool> insert_unique(const value_type& obj)
  {
    // 首先推断容量是否够用, 否则就又一次配置
    resize(num_elements + 1);
    return insert_unique_noresize(obj);
  }

  // 插入操作, 同意反复
  iterator insert_equal(const value_type& obj)
  {
    resize(num_elements + 1);
    return insert_equal_noresize(obj);
  }

  pair<iterator, bool> insert_unique_noresize(const value_type& obj);
  iterator insert_equal_noresize(const value_type& obj);

#ifdef __STL_MEMBER_TEMPLATES
  template <class InputIterator>
  void insert_unique(InputIterator f, InputIterator l)
  {
    insert_unique(f, l, iterator_category(f));
  }

  template <class InputIterator>
  void insert_equal(InputIterator f, InputIterator l)
  {
    insert_equal(f, l, iterator_category(f));
  }

  template <class InputIterator>
  void insert_unique(InputIterator f, InputIterator l,
                     input_iterator_tag)
  {
    for ( ; f != l; ++f)
      insert_unique(*f);
  }

  template <class InputIterator>
  void insert_equal(InputIterator f, InputIterator l,
                    input_iterator_tag)
  {
    for ( ; f != l; ++f)
      insert_equal(*f);
  }

  template <class ForwardIterator>
  void insert_unique(ForwardIterator f, ForwardIterator l,
                     forward_iterator_tag)
  {
    size_type n = 0;
    distance(f, l, n);
    resize(num_elements + n);
    for ( ; n > 0; --n, ++f)
      insert_unique_noresize(*f);
  }

  template <class ForwardIterator>
  void insert_equal(ForwardIterator f, ForwardIterator l,
                    forward_iterator_tag)
  {
    size_type n = 0;
    distance(f, l, n);
    resize(num_elements + n);
    for ( ; n > 0; --n, ++f)
      insert_equal_noresize(*f);
  }

#else /* __STL_MEMBER_TEMPLATES */
  void insert_unique(const value_type* f, const value_type* l)
  {
    size_type n = l - f;
    resize(num_elements + n);
    for ( ; n > 0; --n, ++f)
      insert_unique_noresize(*f);
  }

  void insert_equal(const value_type* f, const value_type* l)
  {
    size_type n = l - f;
    resize(num_elements + n);
    for ( ; n > 0; --n, ++f)
      insert_equal_noresize(*f);
  }

  void insert_unique(const_iterator f, const_iterator l)
  {
    size_type n = 0;
    distance(f, l, n);
    resize(num_elements + n);
    for ( ; n > 0; --n, ++f)
      insert_unique_noresize(*f);
  }

  void insert_equal(const_iterator f, const_iterator l)
  {
    size_type n = 0;
    distance(f, l, n);
    resize(num_elements + n);
    for ( ; n > 0; --n, ++f)
      insert_equal_noresize(*f);
  }
#endif /*__STL_MEMBER_TEMPLATES */

  reference find_or_insert(const value_type& obj);

  // 查找指定key
  iterator find(const key_type& key)
  {
    size_type n = bkt_num_key(key);
    node* first;
    for ( first = buckets[n];
          first && !equals(get_key(first->val), key);
          first = first->next)
      {}
    return iterator(first, this);
  }

  const_iterator find(const key_type& key) const
  {
    size_type n = bkt_num_key(key);
    const node* first;
    for ( first = buckets[n];
          first && !equals(get_key(first->val), key);
          first = first->next)
      {}
    return const_iterator(first, this);
  }

  // 返回key元素的个数
  size_type count(const key_type& key) const
  {
    const size_type n = bkt_num_key(key);
    size_type result = 0;

    for (const node* cur = buckets[n]; cur; cur = cur->next)
      if (equals(get_key(cur->val), key))
        ++result;
    return result;
  }

  pair<iterator, iterator> equal_range(const key_type& key);
  pair<const_iterator, const_iterator> equal_range(const key_type& key) const;

  // 擦除元素
  size_type erase(const key_type& key);
  void erase(const iterator& it);
  void erase(iterator first, iterator last);

  void erase(const const_iterator& it);
  void erase(const_iterator first, const_iterator last);

  void resize(size_type num_elements_hint);
  void clear();

private:
  size_type next_size(size_type n) const { return __stl_next_prime(n); }

  // 预留空间, 并进行初始化
  void initialize_buckets(size_type n)
  {
    const size_type n_buckets = next_size(n);
    buckets.reserve(n_buckets);
    buckets.insert(buckets.end(), n_buckets, (node*) 0);
    num_elements = 0;
  }

  size_type bkt_num_key(const key_type& key) const
  {
    return bkt_num_key(key, buckets.size());
  }

  // 获取obj映射位置, 要经过一个mod过程
  size_type bkt_num(const value_type& obj) const
  {
    return bkt_num_key(get_key(obj));
  }

  size_type bkt_num_key(const key_type& key, size_t n) const
  {
    return hash(key) % n;
  }

  size_type bkt_num(const value_type& obj, size_t n) const
  {
    return bkt_num_key(get_key(obj), n);
  }

  // 分配空间并进行构造
  node* new_node(const value_type& obj)
  {
    node* n = node_allocator::allocate();
    n->next = 0;
    __STL_TRY {
      construct(&n->val, obj);
      return n;
    }
    __STL_UNWIND(node_allocator::deallocate(n));
  }

  // 析构并释放空间
  void delete_node(node* n)
  {
    destroy(&n->val);
    node_allocator::deallocate(n);
  }

  // 解析见实现部分
  void erase_bucket(const size_type n, node* first, node* last);
  void erase_bucket(const size_type n, node* last);

  void copy_from(const hashtable& ht);
};


template <class V, class K, class HF, class ExK, class EqK, class A>
__hashtable_iterator<V, K, HF, ExK, EqK, A>&
__hashtable_iterator<V, K, HF, ExK, EqK, A>::operator++()
{
  const node* old = cur;
  cur = cur->next;              // 当前链表结点的下一个结点, 假设不为0
                                // 那么它就是我们要的

  // 链表结点恰好是最后一个结点, 我们要在线性表的下一个表格的链表中查找
  if (!cur)
  {
    size_type bucket = ht->bkt_num(old->val);
    while (!cur && ++bucket < ht->buckets.size())
      cur = ht->buckets[bucket];
  }

  return *this;
}

template <class V, class K, class HF, class ExK, class EqK, class A>
inline __hashtable_iterator<V, K, HF, ExK, EqK, A>
__hashtable_iterator<V, K, HF, ExK, EqK, A>::operator++(int)
{
  iterator tmp = *this;
  ++*this;      // 触发operator ++()
  return tmp;
}

// const情况同上
template <class V, class K, class HF, class ExK, class EqK, class A>
__hashtable_const_iterator<V, K, HF, ExK, EqK, A>&
__hashtable_const_iterator<V, K, HF, ExK, EqK, A>::operator++()
{
  const node* old = cur;
  cur = cur->next;
  if (!cur) {
    size_type bucket = ht->bkt_num(old->val);
    while (!cur && ++bucket < ht->buckets.size())
      cur = ht->buckets[bucket];
  }
  return *this;
}

template <class V, class K, class HF, class ExK, class EqK, class A>
inline __hashtable_const_iterator<V, K, HF, ExK, EqK, A>
__hashtable_const_iterator<V, K, HF, ExK, EqK, A>::operator++(int)
{
  const_iterator tmp = *this;
  ++*this;
  return tmp;
}

// 对于不支持偏特化的编译器提供traits支持
#ifndef __STL_CLASS_PARTIAL_SPECIALIZATION

template <class V, class K, class HF, class ExK, class EqK, class All>
inline forward_iterator_tag
iterator_category(const __hashtable_iterator<V, K, HF, ExK, EqK, All>&)
{
  return forward_iterator_tag();
}

template <class V, class K, class HF, class ExK, class EqK, class All>
inline V* value_type(const __hashtable_iterator<V, K, HF, ExK, EqK, All>&)
{
  return (V*) 0;
}

template <class V, class K, class HF, class ExK, class EqK, class All>
inline hashtable<V, K, HF, ExK, EqK, All>::difference_type*
distance_type(const __hashtable_iterator<V, K, HF, ExK, EqK, All>&)
{
  return (hashtable<V, K, HF, ExK, EqK, All>::difference_type*) 0;
}

template <class V, class K, class HF, class ExK, class EqK, class All>
inline forward_iterator_tag
iterator_category(const __hashtable_const_iterator<V, K, HF, ExK, EqK, All>&)
{
  return forward_iterator_tag();
}

template <class V, class K, class HF, class ExK, class EqK, class All>
inline V*
value_type(const __hashtable_const_iterator<V, K, HF, ExK, EqK, All>&)
{
  return (V*) 0;
}

template <class V, class K, class HF, class ExK, class EqK, class All>
inline hashtable<V, K, HF, ExK, EqK, All>::difference_type*
distance_type(const __hashtable_const_iterator<V, K, HF, ExK, EqK, All>&)
{
  return (hashtable<V, K, HF, ExK, EqK, All>::difference_type*) 0;
}

#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */

template <class V, class K, class HF, class Ex, class Eq, class A>
bool operator==(const hashtable<V, K, HF, Ex, Eq, A>& ht1,
                const hashtable<V, K, HF, Ex, Eq, A>& ht2)
{
  typedef typename hashtable<V, K, HF, Ex, Eq, A>::node node;
  if (ht1.buckets.size() != ht2.buckets.size())
    return false;
  for (int n = 0; n < ht1.buckets.size(); ++n) {
    node* cur1 = ht1.buckets[n];
    node* cur2 = ht2.buckets[n];
    for ( ; cur1 && cur2 && cur1->val == cur2->val;
          cur1 = cur1->next, cur2 = cur2->next)
      {}
    if (cur1 || cur2)
      return false;
  }
  return true;
}

// 假设编译器支持模板函数特化优先级
// 那么将全局的swap实现为使用hashtable私有的swap以提高效率
#ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER

template <class Val, class Key, class HF, class Extract, class EqKey, class A>
inline void swap(hashtable<Val, Key, HF, Extract, EqKey, A>& ht1,
                 hashtable<Val, Key, HF, Extract, EqKey, A>& ht2) {
  ht1.swap(ht2);
}

#endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */


// 在不须要又一次调整容量的情况下插入元素, key不能够反复
template <class V, class K, class HF, class Ex, class Eq, class A>
pair<typename hashtable<V, K, HF, Ex, Eq, A>::iterator, bool>
hashtable<V, K, HF, Ex, Eq, A>::insert_unique_noresize(const value_type& obj)
{
  // 获取待插入元素在hashtable中的索引
  const size_type n = bkt_num(obj);

  node* first = buckets[n];

  for (node* cur = first; cur; cur = cur->next)
    // 假设keu反复, 在不进行插入, 并告知用户插入失败
    if (equals(get_key(cur->val), get_key(obj)))
      return pair<iterator, bool>(iterator(cur, this), false);

  // 插入结点
  node* tmp = new_node(obj);
  tmp->next = first;
  buckets[n] = tmp;
  ++num_elements;
  return pair<iterator, bool>(iterator(tmp, this), true);
}

// 在不须要又一次调整容量的情况下插入元素, key能够反复
template <class V, class K, class HF, class Ex, class Eq, class A>
typename hashtable<V, K, HF, Ex, Eq, A>::iterator
hashtable<V, K, HF, Ex, Eq, A>::insert_equal_noresize(const value_type& obj)
{
  const size_type n = bkt_num(obj);
  node* first = buckets[n];

  for (node* cur = first; cur; cur = cur->next)
    if (equals(get_key(cur->val), get_key(obj))) {
      node* tmp = new_node(obj);
      tmp->next = cur->next;
      cur->next = tmp;
      ++num_elements;
      return iterator(tmp, this);
    }

  node* tmp = new_node(obj);
  tmp->next = first;
  buckets[n] = tmp;
  ++num_elements;
  return iterator(tmp, this);
}

// 这个用于支持hash_map操作
template <class V, class K, class HF, class Ex, class Eq, class A>
typename hashtable<V, K, HF, Ex, Eq, A>::reference
hashtable<V, K, HF, Ex, Eq, A>::find_or_insert(const value_type& obj)
{
  resize(num_elements + 1);

  size_type n = bkt_num(obj);
  node* first = buckets[n];

  for (node* cur = first; cur; cur = cur->next)
    if (equals(get_key(cur->val), get_key(obj)))
      return cur->val;

  node* tmp = new_node(obj);
  tmp->next = first;
  buckets[n] = tmp;
  ++num_elements;
  return tmp->val;
}

// 查找满足key的区间
template <class V, class K, class HF, class Ex, class Eq, class A>
pair<typename hashtable<V, K, HF, Ex, Eq, A>::iterator,
     typename hashtabfind_or_insertle<V, K, HF, Ex, Eq, A>::iterator>
hashtable<V, K, HF, Ex, Eq, A>::equal_range(const key_type& key)
{
  typedef pair<iterator, iterator> pii;
  const size_type n = bkt_num_key(key);

  for (node* first = buckets[n]; first; first = first->next) {
    if (equals(get_key(first->val), key)) {
      for (node* cur = first->next; cur; cur = cur->next)
        if (!equals(get_key(cur->val), key))
          return pii(iterator(first, this), iterator(cur, this));
      for (size_type m = n + 1; m < buckets.size(); ++m)
        if (buckets[m])
          return pii(iterator(first, this),
                     iterator(buckets[m], this));
      return pii(iterator(first, this), end());
    }
  }
  return pii(end(), end());
}

template <class V, class K, class HF, class Ex, class Eq, class A>
pair<typename hashtable<V, K, HF, Ex, Eq, A>::const_iterator,
     typename hashtable<V, K, HF, Ex, Eq, A>::const_iterator>
hashtable<V, K, HF, Ex, Eq, A>::equal_range(const key_type& key) const
{
  typedef pair<const_iterator, const_iterator> pii;
  const size_type n = bkt_num_key(key);

  for (const node* first = buckets[n] ; first; first = first->next) {
    if (equals(get_key(first->val), key)) {
      for (const node* cur = first->next; cur; cur = cur->next)
        if (!equals(get_key(cur->val), key))
          return pii(const_iterator(first, this),
                     const_iterator(cur, this));
      for (size_type m = n + 1; m < buckets.size(); ++m)
        if (buckets[m])
          return pii(const_iterator(first, this),
                     const_iterator(buckets[m], this));
      return pii(const_iterator(first, this), end());
    }
  }
  return pii(end(), end());
}

// 擦除指定元素
template <class V, class K, class HF, class Ex, class Eq, class A>
typename hashtable<V, K, HF, Ex, Eq, A>::size_type
hashtable<V, K, HF, Ex, Eq, A>::erase(const key_type& key)
{
  // 计算映射位置
  const size_type n = bkt_num_key(key);
  node* first = buckets[n];
  size_type erased = 0;

  // 開始查找并删除
  if (first) {
    node* cur = first;
    node* next = cur->next;
    while (next) {
      if (equals(get_key(next->val), key)) {
        cur->next = next->next;
        delete_node(next);
        next = cur->next;
        ++erased;
        --num_elements;
      }
      else {
        cur = next;
        next = cur->next;
      }
    }
    if (equals(get_key(first->val), key)) {
      buckets[n] = first->next;
      delete_node(first);
      ++erased;
      --num_elements;
    }
  }
  return erased;
}

template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::erase(const iterator& it)
{
  if (node* const p = it.cur) {
    const size_type n = bkt_num(p->val);
    node* cur = buckets[n];

    if (cur == p) {
      buckets[n] = cur->next;
      delete_node(cur);
      --num_elements;
    }
    else {
      node* next = cur->next;
      while (next) {
        if (next == p) {
          cur->next = next->next;
          delete_node(next);
          --num_elements;
          break;
        }
        else {
          cur = next;
          next = cur->next;
        }
      }
    }
  }
}

// 擦除指定区间的元素
template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::erase(iterator first, iterator last)
{
  size_type f_bucket = first.cur ?
 bkt_num(first.cur->val) : buckets.size();
  size_type l_bucket = last.cur ? bkt_num(last.cur->val) : buckets.size();

  if (first.cur == last.cur)
    return;
  else if (f_bucket == l_bucket)
    erase_bucket(f_bucket, first.cur, last.cur);
  else {
    erase_bucket(f_bucket, first.cur, 0);
    for (size_type n = f_bucket + 1; n < l_bucket; ++n)
      erase_bucket(n, 0);
    if (l_bucket != buckets.size())
      erase_bucket(l_bucket, last.cur);
  }
}

template <class V, class K, class HF, class Ex, class Eq, class A>
inline void
hashtable<V, K, HF, Ex, Eq, A>::erase(const_iterator first,
                                      const_iterator last)
{
  erase(iterator(const_cast<node*>(first.cur),
                 const_cast<hashtable*>(first.ht)),
        iterator(const_cast<node*>(last.cur),
                 const_cast<hashtable*>(last.ht)));
}

template <class V, class K, class HF, class Ex, class Eq, class A>
inline void
hashtable<V, K, HF, Ex, Eq, A>::erase(const const_iterator& it)
{
  erase(iterator(const_cast<node*>(it.cur),
                 const_cast<hashtable*>(it.ht)));
}

// 调整hashtable的容量
template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::resize(size_type num_elements_hint)
{
  const size_type old_n = buckets.size();

  // 假设新调整的大小小于当前大小, 不进行更改
  if (num_elements_hint > old_n) {
    const size_type n = next_size(num_elements_hint);

    // 假设已经到达hashtable的容量的极限, 那么也不进行更改
    if (n > old_n) {
      // 建立新的线性表来扩充容量
      vector<node*, A> tmp(n, (node*) 0);
      __STL_TRY {
        // 先面開始copy
        for (size_type bucket = 0; bucket < old_n; ++bucket) {
          node* first = buckets[bucket];
          while (first) {
            size_type new_bucket = bkt_num(first->val, n);
            buckets[bucket] = first->next;
            first->next = tmp[new_bucket];
            tmp[new_bucket] = first;
            first = buckets[bucket];
          }
        }
        buckets.swap(tmp);
      }
#         ifdef __STL_USE_EXCEPTIONS
      catch(...) {
        for (size_type bucket = 0; bucket < tmp.size(); ++bucket) {
          while (tmp[bucket]) {
            node* next = tmp[bucket]->next;
            delete_node(tmp[bucket]);
            tmp[bucket] = next;
          }
        }
        throw;
      }
#         endif /* __STL_USE_EXCEPTIONS */
    }
  }
}

// 擦除指定映射位置的全部元素
template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::erase_bucket(const size_type n,
                                                  node* first, node* last)
{
  node* cur = buckets[n];
  if (cur == first)
    erase_bucket(n, last);
  else {
    node* next;
    for (next = cur->next; next != first; cur = next, next = cur->next)
      ;
    while (next) {
      cur->next = next->next;
      delete_node(next);
      next = cur->next;
      --num_elements;
    }
  }
}

template <class V, class K, class HF, class Ex, class Eq, class A>
void
hashtable<V, K, HF, Ex, Eq, A>::erase_bucket(const size_type n, node* last)
{
  node* cur = buckets[n];
  while (cur != last) {
    node* next = cur->next;
    delete_node(cur);
    cur = next;
    buckets[n] = cur;
    --num_elements;
  }
}

// 清空hashtable, 可是不释放vector的内存
template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::clear()
{
  for (size_type i = 0; i < buckets.size(); ++i) {
    node* cur = buckets[i];
    while (cur != 0) {
      node* next = cur->next;
      delete_node(cur);
      cur = next;
    }
    buckets[i] = 0;
  }
  num_elements = 0;
}

// 复制还有一个hashtable给当前hashtable
template <class V, class K, class HF, class Ex, class Eq, class A>
void hashtable<V, K, HF, Ex, Eq, A>::copy_from(const hashtable& ht)
{
  // 首先清空当前hashtable
  buckets.clear();
  // 预留足够容量
  buckets.reserve(ht.buckets.size());
  // 完毕初始化操作, 这是hashtable的先验条件
  buckets.insert(buckets.end(), ht.buckets.size(), (node*) 0);
  __STL_TRY {
    // 開始copy操作
    for (size_type i = 0; i < ht.buckets.size(); ++i) {
      if (const node* cur = ht.buckets[i]) {
        node* copy = new_node(cur->val);
        buckets[i] = copy;

        for (node* next = cur->next; next; cur = next, next = cur->next) {
          copy->next = new_node(next->val);
          copy = copy->next;
        }
      }
    }
    num_elements = ht.num_elements;
  }
  __STL_UNWIND(clear());
}

__STL_END_NAMESPACE

#endif /* __SGI_STL_INTERNAL_HASHTABLE_H */

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