iflHashTable(3)	  Image	Format Library C++ Reference Manual    iflHashTable(3)

NAME    [Toc]    [Back]

     iflHashTable, iflHashElem - base classes from which hash table
     implementations may be derived

INHERITS FROM    [Toc]    [Back]

     This is a base class.

HEADER FILE    [Toc]    [Back]

     #include <ifl/iflHashTable.h>

CLASS DESCRIPTION    [Toc]    [Back]

     This class	implements an abstract hash-based lookup table.	 To create a
     hash table, a derived class must be defined that specifies	the pure
     virtual match() method.  In addition, a hash function must	be defined and
     used to fill in the hashIndex field of any	hash table elements (derived
     from iflHashElem) that are	to be inserted into the	table.	The match()
     method is then used to compare elements when a collision occurs on	the
     hashIndex field.

     The iflHashElem class is defined as:

	  struct iflHashElem {
	      unsigned int hashIndex;
	  };

     It	is used	as a base from which to	derive classes of elements to be
     inserted into a hash table	derived	from iflHashTable.  The	constructor of
     the derived class should fill in the hashIndex field with an appropriate
     unsigned integer value for	the hash index.	 The hash function used	to map
     a hash element to its hash	index must be carefully	chosed to minimize
     collisions	(different elements mapping to the same	index) to get the best
     performance from the hash table.

CLASS MEMBER FUNCTION SUMMARY    [Toc]    [Back]

     Constructor

	  iflHashTable(int maxEntries=0)

     Manipulating    [Toc]    [Back]

	  void clear()
	  int insert(iflHashElem* elem)
	  int remove(iflHashElem* elem)


     Query    [Toc]    [Back]

	  iflHashElem* find(unsigned int index,	const void* key)
	  iflHashElem* next(int& index)
	  float	getFullFraction() const
	  void setFullFraction(const float frac)




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iflHashTable(3)	  Image	Format Library C++ Reference Manual    iflHashTable(3)



     Key matching    [Toc]    [Back]

	  virtual int match(const void*	key,		       protected
			    const iflHashElem* elem) = 0


     Performance Statistics    [Toc]    [Back]

	  int lookCount;
	  int totalLook;
	  int maxLook;
	  void clearStats()

FUNCTION DESCRIPTIONS    [Toc]    [Back]

     iflHashTable()

	  iflHashTable(int maxEntries=0)


	  Creates an empty iflHashTable, with initial size large enough	to
	  hold maxEntries; the default value of	zero will create a table with
	  131 slots.  By default the hash table	will automatically grow	when
	  it gets more than half full.	See setFullFraction() for more
	  details.

     clear()

	  void clear()


	  Removes all elements currently in the	hash table.

     find()

	  iflHashElem* find(unsigned int index,	const void* key)


	  Finds	the element with hash index, index, and	key value, key.

     getFullFraction()

	  float	getFullFraction() const


	  Returns the current fraction of the table, which when	filled will
	  cause	the hash table to be expanded.	The default value is .5	(50%).

     insert()






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iflHashTable(3)	  Image	Format Library C++ Reference Manual    iflHashTable(3)



	  void insert(iflHashElem* elem)


	  Inserts the hash element, elem, into the hash	table.	The hashIndex
	  field	must already be	filled in.

     match()

	  virtual int match(const void*	key,		       protected
			    const iflHashElem* elem) = 0


	  This function	is used	to compare an element key, key,	with the key
	  of another element, elem.  This function must	be defined in any
	  class	derived	from iflHashTable.

     next()

	  iflHashElem* next(int& index)


	  This function	is used	to iterate through the filled entries of a
	  hash table.  To start	iterating, index should	be initiliazed to
	  zero.	 The index should not be altered on subsequent calls, as
	  iflHashTable uses it to keep track of	where it is in the table.  The
	  returned value is a pointer to the next hash element in the table,
	  or NULL, when	there are no more entries left to iterate on in	the
	  table.

     remove()

	  void remove(iflHashElem* elem)


	  This function	is used	to remove the hash table element, elem,	from
	  the table.

     setFullFraction()

	  void setFullFraction(const float frac)


	  Sets the current fraction of the table, which	when filled will cause
	  the hash table to be expanded.  The default value is .5 (50%).  If
	  frac is 1, the hash table will not grow, and insert()	will fail when
	  the table is full.

     clearStats()

	  void clearStats()





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iflHashTable(3)	  Image	Format Library C++ Reference Manual    iflHashTable(3)



	  Resets the lookCount,	totalLook, and maxLook member variables	to
	  zero.	 lookCount holds a running total of the	number of lookups
	  (calls to find() or locate()).  totalLook holds the number of	hashes
	  and rehashes accumulated over	all lookups.  maxLook holds the
	  maximum number of rehashes ever required by a	single lookup.

SEE ALSO    [Toc]    [Back]

     iflDictionary


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