org.h2.compress

Class CompressLZF

java.lang.Object

org.h2.compress.CompressLZF

All Implemented Interfaces:

Compressor

public final class CompressLZF
extends java.lang.Object
implements Compressor

This class implements the LZF lossless data compression algorithm. LZF is a Lempel-Ziv variant with byte-aligned output, and optimized for speed.

Safety/Use Notes:

• Each instance should be used by a single thread only.
• The data buffers should be smaller than 1 GB.
• For performance reasons, safety checks on expansion are omitted.
• Invalid compressed data can cause an ArrayIndexOutOfBoundsException.

The LZF compressed format knows literal runs and back-references:

• Literal run: directly copy bytes from input to output.
• Back-reference: copy previous data to output stream, with specified offset from location and length. The length is at least 3 bytes.

The first byte of the compressed stream is the control byte. For literal runs, the highest three bits of the control byte are not set, the lower bits are the literal run length, and the next bytes are data to copy directly into the output. For back-references, the highest three bits of the control byte are the back-reference length. If all three bits are set, then the back-reference length is stored in the next byte. The lower bits of the control byte combined with the next byte form the offset for the back-reference.

Field Summary

Fields inherited from interface org.h2.compress.Compressor

DEFLATE, LZF, NO

Constructor Summary

Constructors

Constructor and Description
CompressLZF()

Method Summary

Modifier and Type	Method and Description
int	compress(byte[] in, int inPos, int inLen, byte[] out, int outPos) Compress a number of bytes.
int	compress(java.nio.ByteBuffer in, int inPos, byte[] out, int outPos) Compress a number of bytes.
void	expand(byte[] in, int inPos, int inLen, byte[] out, int outPos, int outLen) Expand a number of compressed bytes.
static void	expand(java.nio.ByteBuffer in, java.nio.ByteBuffer out) Expand a number of compressed bytes.
int	getAlgorithm() Get the compression algorithm type.
void	setOptions(java.lang.String options) Set the compression options.

Methods inherited from class java.lang.Object

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

Constructor Detail

CompressLZF

public CompressLZF()

Method Detail

setOptions

public void setOptions(java.lang.String options)

Description copied from interface: Compressor

Set the compression options. This may include settings for higher performance but less compression.

Specified by:

setOptions in interface Compressor

Parameters:

options - the options

compress

public int compress(byte[] in,
                    int inPos,
                    int inLen,
                    byte[] out,
                    int outPos)

Description copied from interface: Compressor

Compress a number of bytes.

Specified by:

compress in interface Compressor

Parameters:

in - the input data

inPos - the offset at the input array

inLen - the number of bytes to compress

out - the output area

outPos - the offset at the output array

Returns:

the end position

compress

public int compress(java.nio.ByteBuffer in,
                    int inPos,
                    byte[] out,
                    int outPos)

Compress a number of bytes.

Parameters:

in - the input data

inPos - the offset at the input buffer

out - the output area

outPos - the offset at the output array

Returns:

the end position

expand

public void expand(byte[] in,
                   int inPos,
                   int inLen,
                   byte[] out,
                   int outPos,
                   int outLen)

Description copied from interface: Compressor

Expand a number of compressed bytes.

Specified by:

expand in interface Compressor

Parameters:

in - the compressed data

inPos - the offset at the input array

inLen - the number of bytes to read

out - the output area

outPos - the offset at the output array

outLen - the size of the uncompressed data

expand

public static void expand(java.nio.ByteBuffer in,
                          java.nio.ByteBuffer out)

Expand a number of compressed bytes.

Parameters:

in - the compressed data

out - the output area

getAlgorithm

public int getAlgorithm()

Description copied from interface: Compressor

Get the compression algorithm type.

Specified by:

getAlgorithm in interface Compressor

Returns:

the type