org.apache.lucene.util
Class OpenBitSet

java.lang.Object
  org.apache.lucene.search.DocIdSet
      org.apache.lucene.util.OpenBitSet

All Implemented Interfaces:

Serializable, Cloneable, Bits

Direct Known Subclasses:

OpenBitSetDISI

public class OpenBitSet
extends DocIdSet
implements Cloneable, Serializable, Bits

An "open" BitSet implementation that allows direct access to the array of words storing the bits.

Unlike java.util.bitset, the fact that bits are packed into an array of longs is part of the interface. This allows efficient implementation of other algorithms by someone other than the author. It also allows one to efficiently implement alternate serialization or interchange formats.

OpenBitSet is faster than java.util.BitSet in most operations and *much* faster at calculating cardinality of sets and results of set operations. It can also handle sets of larger cardinality (up to 64 * 2**32-1)

The goals of OpenBitSet are the fastest implementation possible, and maximum code reuse. Extra safety and encapsulation may always be built on top, but if that's built in, the cost can never be removed (and hence people re-implement their own version in order to get better performance). If you want a "safe", totally encapsulated (and slower and limited) BitSet class, use java.util.BitSet.

Performance Results

Test system: Pentium 4, Sun Java 1.5_06 -server -Xbatch -Xmx64M
BitSet size = 1,000,000
Results are java.util.BitSet time divided by OpenBitSet time.

	cardinality	intersect_count	union	nextSetBit	get	iterator
50% full	3.36	3.96	1.44	1.46	1.99	1.58
1% full	3.31	3.90		1.04		0.99

Test system: AMD Opteron, 64 bit linux, Sun Java 1.5_06 -server -Xbatch -Xmx64M
BitSet size = 1,000,000
Results are java.util.BitSet time divided by OpenBitSet time.

	cardinality	intersect_count	union	nextSetBit	get	iterator
50% full	2.50	3.50	1.00	1.03	1.12	1.25
1% full	2.51	3.49		1.00		1.02

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.lucene.util.Bits

Bits.MatchAllBits, Bits.MatchNoBits

Field Summary

protected long[]	bits
protected int	wlen

Fields inherited from class org.apache.lucene.search.DocIdSet

EMPTY_DOCIDSET

Fields inherited from interface org.apache.lucene.util.Bits

EMPTY_ARRAY

Constructor Summary

OpenBitSet()

OpenBitSet(long numBits)
Constructs an OpenBitSet large enough to hold numBits.

OpenBitSet(long[] bits, int numWords)
Constructs an OpenBitSet from an existing long[].

Method Summary

void	and(OpenBitSet other)
void	andNot(OpenBitSet other)
static long	andNotCount(OpenBitSet a, OpenBitSet b) Returns the popcount or cardinality of "a and not b" or "intersection(a, not(b))".
static int	bits2words(long numBits) returns the number of 64 bit words it would take to hold numBits
long	capacity() Returns the current capacity in bits (1 greater than the index of the last bit)
long	cardinality()
void	clear(int startIndex, int endIndex) Clears a range of bits.
void	clear(long index) clears a bit, allowing access beyond the current set size without changing the size.
void	clear(long startIndex, long endIndex) Clears a range of bits.
Object	clone()
void	ensureCapacity(long numBits) Ensure that the long[] is big enough to hold numBits, expanding it if necessary.
void	ensureCapacityWords(int numWords) Expand the long[] with the size given as a number of words (64 bit longs).
boolean	equals(Object o) returns true if both sets have the same bits set
protected int	expandingWordNum(long index)
void	fastClear(int index) clears a bit.
void	fastClear(long index) clears a bit.
void	fastFlip(int index) flips a bit.
void	fastFlip(long index) flips a bit.
boolean	fastGet(int index) Returns true or false for the specified bit index.
boolean	fastGet(long index) Returns true or false for the specified bit index.
void	fastSet(int index) Sets the bit at the specified index.
void	fastSet(long index) Sets the bit at the specified index.
void	flip(long index) flips a bit, expanding the set size if necessary
void	flip(long startIndex, long endIndex) Flips a range of bits, expanding the set size if necessary
boolean	flipAndGet(int index) flips a bit and returns the resulting bit value.
boolean	flipAndGet(long index) flips a bit and returns the resulting bit value.
boolean	get(int index) Returns true or false for the specified bit index.
boolean	get(long index) Returns true or false for the specified bit index
boolean	getAndSet(int index) Sets a bit and returns the previous value.
boolean	getAndSet(long index) Sets a bit and returns the previous value.
int	getBit(int index) returns 1 if the bit is set, 0 if not.
long[]	getBits() Expert: returns the long[] storing the bits
int	getNumWords() Expert: gets the number of longs in the array that are in use
int	hashCode()
void	intersect(OpenBitSet other) this = this AND other
static long	intersectionCount(OpenBitSet a, OpenBitSet b) Returns the popcount or cardinality of the intersection of the two sets.
boolean	intersects(OpenBitSet other) returns true if the sets have any elements in common
boolean	isCacheable() This DocIdSet implementation is cacheable.
boolean	isEmpty() Returns true if there are no set bits
DocIdSetIterator	iterator() Provides a DocIdSetIterator to access the set.
int	length()
int	nextSetBit(int index) Returns the index of the first set bit starting at the index specified.
long	nextSetBit(long index) Returns the index of the first set bit starting at the index specified.
void	or(OpenBitSet other)
int	prevSetBit(int index) Returns the index of the first set bit starting downwards at the index specified.
long	prevSetBit(long index) Returns the index of the first set bit starting downwards at the index specified.
void	remove(OpenBitSet other) Remove all elements set in other.
void	set(long index) sets a bit, expanding the set size if necessary
void	set(long startIndex, long endIndex) Sets a range of bits, expanding the set size if necessary
void	setBits(long[] bits) Expert: sets a new long[] to use as the bit storage
void	setNumWords(int nWords) Expert: sets the number of longs in the array that are in use
long	size() Returns the current capacity of this set.
void	trimTrailingZeros() Lowers numWords, the number of words in use, by checking for trailing zero words.
void	union(OpenBitSet other) this = this OR other
static long	unionCount(OpenBitSet a, OpenBitSet b) Returns the popcount or cardinality of the union of the two sets.
void	xor(OpenBitSet other) this = this XOR other
static long	xorCount(OpenBitSet a, OpenBitSet b) Returns the popcount or cardinality of the exclusive-or of the two sets.

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Field Detail

bits

protected long[] bits

wlen

protected int wlen

Constructor Detail

OpenBitSet

public OpenBitSet(long numBits)

Constructs an OpenBitSet large enough to hold numBits.

Parameters:

numBits -

OpenBitSet

public OpenBitSet()

OpenBitSet

public OpenBitSet(long[] bits,
                  int numWords)

Constructs an OpenBitSet from an existing long[].
The first 64 bits are in long[0], with bit index 0 at the least significant bit, and bit index 63 at the most significant. Given a bit index, the word containing it is long[index/64], and it is at bit number index%64 within that word.

numWords are the number of elements in the array that contain set bits (non-zero longs). numWords should be <= bits.length, and any existing words in the array at position >= numWords should be zero.

Method Detail

iterator

public DocIdSetIterator iterator()

Description copied from class: DocIdSet

Provides a DocIdSetIterator to access the set. This implementation can return null or DocIdSet.EMPTY_DOCIDSET.iterator() if there are no docs that match.

Specified by:

iterator in class DocIdSet

isCacheable

public boolean isCacheable()

This DocIdSet implementation is cacheable.

Overrides:

isCacheable in class DocIdSet

capacity

public long capacity()

Returns the current capacity in bits (1 greater than the index of the last bit)

size

public long size()

Returns the current capacity of this set. Included for compatibility. This is *not* equal to cardinality()

length

public int length()

Specified by:

length in interface Bits

isEmpty

public boolean isEmpty()

Returns true if there are no set bits

getBits

public long[] getBits()

Expert: returns the long[] storing the bits

setBits

public void setBits(long[] bits)

Expert: sets a new long[] to use as the bit storage

getNumWords

public int getNumWords()

Expert: gets the number of longs in the array that are in use

setNumWords

public void setNumWords(int nWords)

Expert: sets the number of longs in the array that are in use

get

public boolean get(int index)

Returns true or false for the specified bit index.

Specified by:

get in interface Bits

fastGet

public boolean fastGet(int index)

Returns true or false for the specified bit index. The index should be less than the OpenBitSet size

get

public boolean get(long index)

Returns true or false for the specified bit index

fastGet

public boolean fastGet(long index)

Returns true or false for the specified bit index. The index should be less than the OpenBitSet size.

getBit

public int getBit(int index)

returns 1 if the bit is set, 0 if not. The index should be less than the OpenBitSet size

set

public void set(long index)

sets a bit, expanding the set size if necessary

fastSet

public void fastSet(int index)

Sets the bit at the specified index. The index should be less than the OpenBitSet size.

fastSet

public void fastSet(long index)

Sets the bit at the specified index. The index should be less than the OpenBitSet size.

set

public void set(long startIndex,
                long endIndex)

Sets a range of bits, expanding the set size if necessary

Parameters:

startIndex - lower index

endIndex - one-past the last bit to set

expandingWordNum

protected int expandingWordNum(long index)

fastClear

public void fastClear(int index)

clears a bit. The index should be less than the OpenBitSet size.

fastClear

public void fastClear(long index)

clears a bit. The index should be less than the OpenBitSet size.

clear

public void clear(long index)

clears a bit, allowing access beyond the current set size without changing the size.

clear

public void clear(int startIndex,
                  int endIndex)

Clears a range of bits. Clearing past the end does not change the size of the set.

Parameters:

startIndex - lower index

endIndex - one-past the last bit to clear

clear

public void clear(long startIndex,
                  long endIndex)

Clears a range of bits. Clearing past the end does not change the size of the set.

Parameters:

startIndex - lower index

endIndex - one-past the last bit to clear

getAndSet

public boolean getAndSet(int index)

Sets a bit and returns the previous value. The index should be less than the OpenBitSet size.

getAndSet

public boolean getAndSet(long index)

Sets a bit and returns the previous value. The index should be less than the OpenBitSet size.

fastFlip

public void fastFlip(int index)

flips a bit. The index should be less than the OpenBitSet size.

fastFlip

public void fastFlip(long index)

flips a bit. The index should be less than the OpenBitSet size.

flip

public void flip(long index)

flips a bit, expanding the set size if necessary

flipAndGet

public boolean flipAndGet(int index)

flips a bit and returns the resulting bit value. The index should be less than the OpenBitSet size.

flipAndGet

public boolean flipAndGet(long index)

flips a bit and returns the resulting bit value. The index should be less than the OpenBitSet size.

flip

public void flip(long startIndex,
                 long endIndex)

Flips a range of bits, expanding the set size if necessary

Parameters:

startIndex - lower index

endIndex - one-past the last bit to flip

cardinality

public long cardinality()

Returns:

the number of set bits

intersectionCount

public static long intersectionCount(OpenBitSet a,
                                     OpenBitSet b)

Returns the popcount or cardinality of the intersection of the two sets. Neither set is modified.

unionCount

public static long unionCount(OpenBitSet a,
                              OpenBitSet b)

Returns the popcount or cardinality of the union of the two sets. Neither set is modified.

andNotCount

public static long andNotCount(OpenBitSet a,
                               OpenBitSet b)

Returns the popcount or cardinality of "a and not b" or "intersection(a, not(b))". Neither set is modified.

xorCount

public static long xorCount(OpenBitSet a,
                            OpenBitSet b)

Returns the popcount or cardinality of the exclusive-or of the two sets. Neither set is modified.

nextSetBit

public int nextSetBit(int index)

Returns the index of the first set bit starting at the index specified. -1 is returned if there are no more set bits.

nextSetBit

public long nextSetBit(long index)

Returns the index of the first set bit starting at the index specified. -1 is returned if there are no more set bits.

prevSetBit

public int prevSetBit(int index)

Returns the index of the first set bit starting downwards at the index specified. -1 is returned if there are no more set bits.

prevSetBit

public long prevSetBit(long index)

Returns the index of the first set bit starting downwards at the index specified. -1 is returned if there are no more set bits.

clone

public Object clone()

Overrides:

clone in class Object

intersect

public void intersect(OpenBitSet other)

this = this AND other

union

public void union(OpenBitSet other)

this = this OR other

remove

public void remove(OpenBitSet other)

Remove all elements set in other. this = this AND_NOT other

xor

public void xor(OpenBitSet other)

this = this XOR other

and

public void and(OpenBitSet other)

or

public void or(OpenBitSet other)

andNot

public void andNot(OpenBitSet other)

intersects

public boolean intersects(OpenBitSet other)

returns true if the sets have any elements in common

ensureCapacityWords

public void ensureCapacityWords(int numWords)

Expand the long[] with the size given as a number of words (64 bit longs). getNumWords() is unchanged by this call.

ensureCapacity

public void ensureCapacity(long numBits)

Ensure that the long[] is big enough to hold numBits, expanding it if necessary. getNumWords() is unchanged by this call.

trimTrailingZeros

public void trimTrailingZeros()

Lowers numWords, the number of words in use, by checking for trailing zero words.

bits2words

public static int bits2words(long numBits)

returns the number of 64 bit words it would take to hold numBits

equals

public boolean equals(Object o)

returns true if both sets have the same bits set

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object