H2 Database Engine 2.3.232 · org.h2.compress.CompressLZF

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

Modifier and Type	Field and Description
private int[]	cachedHashTable Hash table for matching byte sequences (reused for performance).
private static final int	HASH_SIZE The number of entries in the hash table.
private static final int	MAX_LITERAL The maximum number of literals in a chunk (32).
private static final int	MAX_OFF The maximum offset allowed for a back-reference (8192).
private static final int	MAX_REF The maximum back-reference length (264).

Constructor Summary

Access	Constructor and Description
public	CompressLZF()

Method Summary

Modifier and Type	Method and Description
public int	compress(byte[] the input data in, int the offset at the input array inPos, int the number of bytes to compress inLen, byte[] the output area out, int the offset at the output array outPos) Implements org.h2.compress.Compressor.compress. Compress a number of bytes.
public int	Returns: the end position compress(ByteBuffer the input data in, int the offset at the input buffer inPos, byte[] the output area out, int the offset at the output array outPos) Compress a number of bytes.
public void	expand(byte[] the compressed data in, int the offset at the input array inPos, int the number of bytes to read inLen, byte[] the output area out, int the offset at the output array outPos, int the size of the uncompressed data outLen) Implements org.h2.compress.Compressor.expand. Expand a number of compressed bytes.
public static void	expand(ByteBuffer the compressed data in, ByteBuffer the output area out) Expand a number of compressed bytes.
private static int	first(byte[] in, int inPos) Return the integer with the first two bytes 0, then the bytes at the index, then at index+1.
private static int	first(ByteBuffer in, int inPos) Return the integer with the first two bytes 0, then the bytes at the index, then at index+1.
public int	getAlgorithm() Implements org.h2.compress.Compressor.getAlgorithm. Get the compression algorithm type.
private static int	hash(int h) Compute the address in the hash table.
private static int	next(int v, byte[] in, int inPos) Shift the value 1 byte left, and add the byte at index inPos+2.
private static int	next(int v, ByteBuffer in, int inPos) Shift the value 1 byte left, and add the byte at index inPos+2.
public void	setOptions(String the options options) Implements org.h2.compress.Compressor.setOptions. Set the compression options.

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

Field Detail

cachedHashTable	back to summary
private int[] cachedHashTable Hash table for matching byte sequences (reused for performance).

HASH_SIZE	back to summary
private static final int HASH_SIZE The number of entries in the hash table. The size is a trade-off between hash collisions (reduced compression) and speed (amount that fits in CPU cache).

MAX_LITERAL	back to summary
private static final int MAX_LITERAL The maximum number of literals in a chunk (32).

MAX_OFF	back to summary
private static final int MAX_OFF The maximum offset allowed for a back-reference (8192).

MAX_REF	back to summary
private static final int MAX_REF The maximum back-reference length (264).

Constructor Detail

CompressLZF	back to summary
public CompressLZF()

Method Detail

compress	back to summary
public int compress(byte[] in, int inPos, int inLen, byte[] out, int outPos) Implements org.h2.compress.Compressor.compress. Doc from org.h2.compress.Compressor.compress. Compress a number of bytes. Parameters in:byte[] the input data inPos:int the offset at the input array inLen:int the number of bytes to compress out:byte[] the output area outPos:int the offset at the output array Returns:int the end position Annotations @Override

compress

back to summary

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

Implements org.h2.compress.Compressor.compress.

Doc from org.h2.compress.Compressor.compress.

Compress a number of bytes.

Parameters

in:byte[]: the input data
inPos:int: the offset at the input array
inLen:int: the number of bytes to compress
out:byte[]: the output area
outPos:int: the offset at the output array

Returns:int

the end position

Annotations

@Override

compress	back to summary
public int compress(ByteBuffer in, int inPos, byte[] out, int outPos) Compress a number of bytes. Parameters in:ByteBuffer the input data inPos:int the offset at the input buffer out:byte[] the output area outPos:int the offset at the output array Returns:int the end position

compress

back to summary

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

Compress a number of bytes.

Parameters

in:ByteBuffer: the input data
inPos:int: the offset at the input buffer
out:byte[]: the output area
outPos:int: the offset at the output array

Returns:int

the end position

expand	back to summary
public void expand(byte[] in, int inPos, int inLen, byte[] out, int outPos, int outLen) Implements org.h2.compress.Compressor.expand. Doc from org.h2.compress.Compressor.expand. Expand a number of compressed bytes. Parameters in:byte[] the compressed data inPos:int the offset at the input array inLen:int the number of bytes to read out:byte[] the output area outPos:int the offset at the output array outLen:int the size of the uncompressed data Annotations @Override

expand

back to summary

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

Implements org.h2.compress.Compressor.expand.

Doc from org.h2.compress.Compressor.expand.

Expand a number of compressed bytes.

Parameters

in:byte[]: the compressed data
inPos:int: the offset at the input array
inLen:int: the number of bytes to read
out:byte[]: the output area
outPos:int: the offset at the output array
outLen:int: the size of the uncompressed data

Annotations

@Override

expand	back to summary
public static void expand(ByteBuffer in, ByteBuffer out) Expand a number of compressed bytes. Parameters in:ByteBuffer the compressed data out:ByteBuffer the output area

expand

back to summary

public static void expand(ByteBuffer in, ByteBuffer out)

Expand a number of compressed bytes.

Parameters

in:ByteBuffer: the compressed data
out:ByteBuffer: the output area

first	back to summary
private static int first(byte[] in, int inPos) Return the integer with the first two bytes 0, then the bytes at the index, then at index+1.

first	back to summary
private static int first(ByteBuffer in, int inPos) Return the integer with the first two bytes 0, then the bytes at the index, then at index+1.

getAlgorithm	back to summary
public int getAlgorithm() Implements org.h2.compress.Compressor.getAlgorithm. Doc from org.h2.compress.Compressor.getAlgorithm. Get the compression algorithm type. Returns:int the type Annotations @Override

getAlgorithm

back to summary

public int getAlgorithm()

Implements org.h2.compress.Compressor.getAlgorithm.

Doc from org.h2.compress.Compressor.getAlgorithm.

Get the compression algorithm type.

Returns:int

the type

Annotations

@Override

hash	back to summary
private static int hash(int h) Compute the address in the hash table.

next	back to summary
private static int next(int v, byte[] in, int inPos) Shift the value 1 byte left, and add the byte at index inPos+2.

next	back to summary
private static int next(int v, ByteBuffer in, int inPos) Shift the value 1 byte left, and add the byte at index inPos+2.

setOptions	back to summary
public void setOptions(String options) Implements org.h2.compress.Compressor.setOptions. Doc from org.h2.compress.Compressor.setOptions. Set the compression options. This may include settings for higher performance but less compression. Parameters options:String the options Annotations @Override

setOptions

back to summary

public void setOptions(String options)

Implements org.h2.compress.Compressor.setOptions.

Doc from org.h2.compress.Compressor.setOptions.

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

Parameters

options:String: the options

Annotations

@Override

public final Class CompressLZF

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail