## 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`

Copyright © 2012 The Apache Software Foundation