/**\hashtable.h * Describes the HashFunction, HashFunctionString, and HashTable classes. It * was just easier to put them all in one set of files. *@author Mike Buland */ #ifndef HASH_TABLE_H #define HASH_TABLE_H //Uncomment this line to see a cool text-mode visualization of what's going on //#define HASH_DEBUG_VIS 1 #include #include #include #include "hashfunction.h" /** * A simple yet flexable hash-table. This uses several tricks to help ensure * that the table is always running at maximum efficiency. You no longer have * to specify a "danger fill level" when more space is needed a rehash is * automatically trigered. Deleting elements is fully supported, as well as * duplicate elements. To work with and allow duplicates simple construct your * HashTable the way you normally would, but when deleting or getting elements * you can specify a skip value. This effectively allows you to treat elements * with duplicate ID's as though they were in a zero-based array. The first * element inserted with a given ID would be at skip zero, the next at skip 1 * and so on. This allows you to quickly search for elements with duplicate * names, just stop when you get a null for a skip number, i.e. *
 *   for( int j = 0;; j++ )
 *   {
 *       void *pData = hash.get( myID, j );
 *       if( !pData ) break;
 *       // Do something interesting with pData
 *   }
 * 
* There are new features in this HashTable that also allow for memory saving * when dealing with systems where many elements are being deleted from the * table. In those cases the elements deleted cannot be simply deleted, instead * they have to be marked as deleted and hidden from the user, but maintained in * the table so that future hashing operations don't fail. When rehashing * occurs all elements marked as deleted are quietly removed. In these cases, * if the number of deleted items would free enough space in the table for the * table to be used efficiently without resizing, it is left the same size and * rehashing is performed effectively in place, allowing the deleted items to * be removed. *
* For info on adding new hashing algorithms, please see the HashFunction class. *@author Mike Buland *@todo Fix probing for tables that allow duplicates, and delete an item, then * insert an item with the same name. */ class HashTable { public: /** Constructs a hash table. *@param hNewFunc A pointer to a hashfunction class to use. If this is * null the default general string type will be used. *@param nInitSize The initial size of the hashtable. *@param bAllowDupes Setting this value to true allows the system to * insert more than one copy of any given key. This can be tricky, and * will require you to use the nSkip parameter on the get function. */ HashTable( HashFunction *hNewFunc, unsigned long int nInitSize, bool bAllowDupes=false ); /** * Destroys the hashtable, cleaning up all internal storage, but not stored * elements. Also deletes the HashFunction passed in in the constructor. */ ~HashTable(); /** Inserts an item into the hashtable. This function will trigger a * rehash if adding another item would force the table's load factor over * the danger level. *@param id used to find the data later. *@param data The data item to insert into the table with the identifier * id *@returns True if insertion was successfull, and false if it failed. */ bool insert( const void *id, const void *data ); /** Gets an item in the hashtable based on the id of that item. If there * is more than one item with the same id you can use the nSkip parameter * to access all of them. *@param id The id of the item you're trying to find. *@param nSkip The number of items with that id to skip before returning * with the requested item. *@returns A pointer to the data stored at the given id. */ const void *get( const void *id, unsigned long int nSkip=0 ); /** Gets the total capacity of the hashtable. This is actually the number * of total positions available inside the hashtable at the moment. This * will change when the hashtable's load exceeds the danger level. * Please note that this is NOT the actual amount of space available. * In reality you can only access about 45-50 percent of that space. *@returns The total capacity. */ unsigned long int getCapacity(); /** Gets the number of filled in items in the hash table. This is roughly * equivelent to the getSize function assosiated with the Lists. *@returns The number of filled in items in the hash table. */ unsigned long int getSize(); /** Gets the load (percentage) of filled in items in the table. This is * technically the size divided by the capacity, but is definately usefull * since it's required to check if it's time to rehash. *@returns The table load in the range 0.0 to 1.0 */ double getLoad(); /** Sets up an xPos object for use indexing the items in the table. Call * this first and follow the directions for getNextItemPos below to * iterate through every item in the table, while avoiding the empty * spaces. *@returns A pointer to a xPos object telling the hashtable where to find * the item you're looking at. */ void *getFirstItemPos(); /** Get the item's data that is being pointed to by xPos. This is only * valid after xPos was created using getFirstItemPos and getNextItemPos * was called at least once. *@param xPos supplied by getFirstItemPos. *@returns The key value that was used to insert the data into the table. */ const void *getItemData( void *xPos ); /** Get the item's ID that is being pointed to by xPos. This is only * valid after xPos was created using getFirstItemPos and getNextItemPos * was called at least once. *@param xPos supplied by getFirstItemPos. *@returns The key value that was used to insert the data into the table. */ const void *getItemID( void *xPos ); /** Used for iterating through a hash table sequentially. This will * update the xPos pointer to point to the next time, all ready to * be accessed with getItemID and getItemData. This must be called at * least once before xPos is meaningful, and will return a NULL when it * has reached the last item. *@param xPos This must be an object created by a call to the function * getFirstItemPos, and is only meaningful to the internal routines. * Aborting a call in the middle (not running to the end of the table) * may result in a memory leak at the moment. *@returns xPos if still iterating through the list, otherwise it will * return NULL when the end has been reached and the xPos variable has * been deleted. */ void *getNextItemPos( void *xPos ); /** A helpful operator to make accessing items easier. Please note that * this simply returns a pointer to the data stored internally, and cannot * be used like the STL operator to store new data, use insert for that. *@param id The identifier used to store the requested item. *@returns The data value assosiated with the given id, or NULL if it * wasn't found in the table. */ const void *operator[](const void *id); /** * Delete the specified item from the hashtable. This actually keeps the * data and marks it deleted. For all intents and purposes to the user it * is deleted, except that the space is still used until a rehash is forced. * This means that in hashtables where elements are being inserted and * deleted frequently you may run into a higher rate of expansion. *@param id The ID to delete. *@param nSkip The number of similar id's to skip before deleting in a * hashtable that allows duplicates. *@returns True if the element was found and deleted, false otherwise. */ bool del( const void *id, int nSkip=0 ); /** * Deletes every entry in the hash table. See the notes on del to see what * this means, except that since no data is being kept, the entire table is * just marked as usable space. */ void clear(); private: /** * Contains info related to a position in the hashtable. Used for * searching through hashtables one item at a time, in order. This class * should never be created by anything but a HashTable, and should never * be referenced directly. Instead the hashtable returns a void pointer, * which is what should be passed back in next time you use a search * function. Always finish a search, since the object is deleted at the * end of the search. *@author Mike Buland */ class HashPos { public: /** Create a blank HashPos. */ HashPos() { bStarted=false; nPos = 0; }; /** Has the search been started? */ bool bStarted; /** The position (index) into the backend storage structure. */ unsigned long int nPos; }; /** * All data related to a single element in the hashtable. This should * really only be used and manipulated by the HashTable itself. *@author Mike Buland */ typedef struct HashNode { public: /** Create a new, empty HashNode. */ HashNode() { id = NULL; data = NULL; bDeleted = false; }; /** A pointer to the original ID that was used to key the data. */ const void *id; /** A pointer to the data stored along with the above ID. */ const void *data; /** Weather or not this data should really...exist */ bool bDeleted; } HashNode; private: /** * Just sets the values in the element to some friendly values. *@param newID The new ID to store. *@param newData The new Data to store. */ void set( int j, const void *newID, const void *newData ); /** * Tells you if the node is filled or not. *@returns True=an ID has been stored here, False=no ID. */ bool isFilled( int j ); /** * This actually resizes, but since every resize requires a reHash to go * along with it, that's the name. This actually creates a new buffer for * all of the contained data and then pulls every old element that was in * the old table out and performs the hashing placement calculations again. * This function skips all data that was marked as deleted, so at this * point it really will be. *@param nNewSize The new size to set the table to while re-hashing. *@returns True if the operation was successful, false otherwise. */ bool reHash( unsigned long int nNewSize ); /** * Helper function to allocate a new table. Really just does the memory * allocation. *@param nNewSize The size of the table to generate. *@returns A new, blank array of HashNode objects the size you specified. */ HashNode *newTable( unsigned long int nNewSize ); /** * This function is used once an actual hash code is obtained. nStart is * the given hash code, which is then wrapped to the size of the table. If * there is data at that location, tests are performed to see if it's the * right one. If it is, then it is returned, otherwise a series of further * tests based on a 2^n search pattern is performed. The position of the * requested data in the back-end storage is returned if found, otherwise * another less useful value is returned... *@param nStart The initial hashcode of the ID testing for. *@param id A pointer to the id that is being searched for. *@returns The real location of the data requested. */ unsigned long int probe( unsigned long int nStart, const void *id ); /** * Simple helper function to determine if a number is prime or not. * This function runs in sqrt(n) time. *@param num Number to test for prime-hood. *@returns True if the number is prime, false otherwise. */ bool isPrime( int num ); /** * Given any number, this function finds the first number after it that is * prime. Since this number is a multiple internally it's rare that the * starting number would be prime. *@param base The number to start the prime search on. *@returns The first prime after the number given. */ int nextPrime( int base ); #ifdef HASH_DEBUG_VIS void printDebugLine( const char *exData ); #endif /** A pointer to the HashFunction subclass instance to use. */ HashFunction *hFunc; /** The complete array of HashNode objects to store data in. */ HashNode *aTable; /** The actual size of the table, not how many elements are in it. */ unsigned long int nTableSize; /** The number of elements that are in the table. */ unsigned long int nSize; /** The number of elements that are unavailable now. */ unsigned long int nFilled; /** Allow duplicate ID's in the table. */ bool bAllowDupes; }; #endif