org.apache.cassandra.utils.obs
Class OpenBitSet

java.lang.Object
  org.apache.cassandra.utils.obs.OpenBitSet

All Implemented Interfaces:

java.io.Serializable

public class OpenBitSet
extends java.lang.Object
implements java.io.Serializable

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

Field Summary

protected long[][]	bits
protected static int	PAGE_SIZE length of bits[][] page in long[] elements.
protected int	wlen

Constructor Summary

OpenBitSet()

OpenBitSet(java.util.BitSet bits)
Contructs an OpenBitset from a BitSet

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

OpenBitSet(long numBits, boolean allocatePages)

Method Summary

void	and(OpenBitSet other)
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.
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(java.lang.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.
int	getNumWords() Expert: gets the number of longs in the array that are in use
long[]	getPage(int pageIdx)
int	getPageCount()
int	getPageSize()
int	hashCode()
void	intersect(OpenBitSet other) this = this AND other
boolean	isEmpty() Returns true if there are no set bits
long	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	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
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.

Methods inherited from class java.lang.Object

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

Field Detail

bits

protected long[][] bits

wlen

protected int wlen

PAGE_SIZE

protected static final int PAGE_SIZE

length of bits[][] page in long[] elements. Choosing unform size for all sizes of bitsets fight fragmentation for very large bloom filters.

See Also:

Constant Field Values

Constructor Detail

OpenBitSet

public OpenBitSet(long numBits)

Constructs an OpenBitSet large enough to hold numBits.

Parameters:

numBits -

OpenBitSet

public OpenBitSet(long numBits,
                  boolean allocatePages)

OpenBitSet

public OpenBitSet()

OpenBitSet

public OpenBitSet(java.util.BitSet bits)

Contructs an OpenBitset from a BitSet

Method Detail

getPageSize

public int getPageSize()

Returns:

the pageSize

getPageCount

public int getPageCount()

getPage

public long[] getPage(int pageIdx)

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 long length()

isEmpty

public boolean isEmpty()

Returns true if there are no set bits

getNumWords

public int getNumWords()

Expert: gets 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.

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

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.

intersect

public void intersect(OpenBitSet other)

this = this AND other

and

public void and(OpenBitSet other)

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(java.lang.Object o)

returns true if both sets have the same bits set

Overrides:

equals in class java.lang.Object

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object