org.apache.lucene.util.packed

Class BlockPackedWriter

java.lang.Object

org.apache.lucene.util.packed.BlockPackedWriter

public final class BlockPackedWriter
extends Object

A writer for large sequences of longs.

The sequence is divided into fixed-size blocks and for each block, the difference between each value and the minimum value of the block is encoded using as few bits as possible. Memory usage of this class is proportional to the block size. Each block has an overhead between 1 and 10 bytes to store the minimum value and the number of bits per value of the block.

Format:

• <BLock>^BlockCount
• BlockCount: ValueCount / BlockSize
• Block: <Header, (Ints)>
• Header: <Token, (MinValue)>
• Token: a byte, first 7 bits are the number of bits per value (bitsPerValue). If the 8th bit is 1, then MinValue (see next) is 0, otherwise MinValue and needs to be decoded
• MinValue: a zigzag-encoded variable-length long whose value should be added to every int from the block to restore the original values
• Ints: If the number of bits per value is 0, then there is nothing to decode and all ints are equal to MinValue. Otherwise: BlockSize packed ints encoded on exactly bitsPerValue bits per value. They are the subtraction of the original values and MinValue

See Also:

BlockPackedReaderIterator, BlockPackedReader

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

Field Summary

Fields

Modifier and Type	Field and Description
protected byte[]	blocks
protected boolean	finished
protected int	off
protected long	ord
protected DataOutput	out
protected long[]	values

Constructor Summary

Constructors

Constructor and Description
BlockPackedWriter(DataOutput out, int blockSize) Sole constructor.

Method Summary

Modifier and Type	Method and Description
void	add(long l) Append a new long.
void	finish() Flush all buffered data to disk.
protected void	flush()
long	ord() Return the number of values which have been added.
void	reset(DataOutput out) Reset this writer to wrap out.
protected void	writeValues(int bitsRequired)

Methods inherited from class java.lang.Object

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

Field Detail

out

protected DataOutput out

values

protected final long[] values

blocks

protected byte[] blocks

off

protected int off

ord

protected long ord

finished

protected boolean finished

Constructor Detail

BlockPackedWriter

public BlockPackedWriter(DataOutput out,
                         int blockSize)

Sole constructor.

Parameters:

blockSize - the number of values of a single block, must be a power of 2

Method Detail

flush

protected void flush()
              throws IOException

Throws:

IOException

reset

public void reset(DataOutput out)

Reset this writer to wrap out. The block size remains unchanged.

add

public void add(long l)
         throws IOException

Append a new long.

Throws:

IOException

finish

public void finish()
            throws IOException

Flush all buffered data to disk. This instance is not usable anymore after this method has been called until reset(DataOutput) has been called.

Throws:

IOException

ord

public long ord()

Return the number of values which have been added.

writeValues

protected final void writeValues(int bitsRequired)
                          throws IOException

Throws:

IOException