BasicHashTable.hh

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// Copyright (c) 1996-2022 Live Networks, Inc.  All rights reserved.
// Basic Hash Table implementation
// C++ header
 
#ifndef _BASIC_HASH_TABLE_HH
#define _BASIC_HASH_TABLE_HH
 
#ifndef _HASH_TABLE_HH
#include "HashTable.hh"
#endif
#ifndef _NET_COMMON_H
#include <NetCommon.h> // to ensure that "uintptr_t" is defined
#endif
 
// A simple hash table implementation, inspired by the hash table
// implementation used in Tcl 7.6: <http://www.tcl.tk/>
 
#define SMALL_HASH_TABLE_SIZE 4
 
class BasicHashTable: public HashTable {
private:
        class TableEntry; // forward
 
public:
  BasicHashTable(int keyType);
  virtual ~BasicHashTable();
 
  // Used to iterate through the members of the table:
  class Iterator; friend class Iterator; // to make Sun's C++ compiler happy
  class Iterator: public HashTable::Iterator {
  public:
    Iterator(BasicHashTable const& table);
 
  private: // implementation of inherited pure virtual functions
    void* next(char const*& key); // returns 0 if none
 
  private:
    BasicHashTable const& fTable;
    unsigned fNextIndex; // index of next bucket to be enumerated after this
    TableEntry* fNextEntry; // next entry in the current bucket
  };
 
private: // implementation of inherited pure virtual functions
  virtual void* Add(char const* key, void* value);
  // Returns the old value if different, otherwise 0
  virtual Boolean Remove(char const* key);
  virtual void* Lookup(char const* key) const;
  // Returns 0 if not found
  virtual unsigned numEntries() const;
 
private:
  class TableEntry {
  public:
    TableEntry* fNext;
    char const* key;
    void* value;
  };
 
  TableEntry* lookupKey(char const* key, unsigned& index) const;
    // returns entry matching "key", or NULL if none
  Boolean keyMatches(char const* key1, char const* key2) const;
    // used to implement "lookupKey()"
 
  TableEntry* insertNewEntry(unsigned index, char const* key);
    // creates a new entry, and inserts it in the table
  void assignKey(TableEntry* entry, char const* key);
    // used to implement "insertNewEntry()"
 
  void deleteEntry(unsigned index, TableEntry* entry);
  void deleteKey(TableEntry* entry);
    // used to implement "deleteEntry()"
 
  void rebuild(); // rebuilds the table as its size increases
 
  unsigned hashIndexFromKey(char const* key) const;
    // used to implement many of the routines above
 
  unsigned randomIndex(uintptr_t i) const {
    return (unsigned)(((i*1103515245) >> fDownShift) & fMask);
  }
 
private:
  TableEntry** fBuckets; // pointer to bucket array
  TableEntry* fStaticBuckets[SMALL_HASH_TABLE_SIZE];// used for small tables
  unsigned fNumBuckets, fNumEntries, fRebuildSize, fDownShift, fMask;
  int fKeyType;
};
 
#endif