Package org.apache.lucene.util.compress

Class LZ4

java.lang.Object

org.apache.lucene.util.compress.LZ4

public final class LZ4
extends Object

LZ4 compression and decompression routines.

https://github.com/lz4/lz4/tree/dev/lib http://fastcompression.blogspot.fr/p/lz4.html

The high-compression option is a simpler version of the one of the original algorithm, and only retains a better hash table that remembers about more occurrences of a previous 4-bytes sequence, and removes all the logic about handling of the case when overlapping matches are found.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final class	LZ4.FastCompressionHashTable	Simple lossy LZ4.HashTable that only stores the last ocurrence for each hash on 2^14 bytes of memory.
static final class	LZ4.HighCompressionHashTable	A higher-precision LZ4.HashTable.

Field Summary

Fields

Modifier and Type	Field	Description
static final int	MAX_DISTANCE	Window size: this is the maximum supported distance between two strings so that LZ4 can replace the second one by a reference to the first one.

Method Summary

Modifier and Type	Method	Description
static void	compress(byte[] bytes, int off, int len, DataOutput out, org.apache.lucene.util.compress.LZ4.HashTable ht)	Compress bytes[off:off+len] into out using at most 16kB of memory.
static void	compressWithDictionary(byte[] bytes, int dictOff, int dictLen, int len, DataOutput out, org.apache.lucene.util.compress.LZ4.HashTable ht)	Compress bytes[dictOff+dictLen:dictOff+dictLen+len] into out using at most 16kB of memory.
static int	decompress(DataInput compressed, int decompressedLen, byte[] dest, int dOff)	Decompress at least decompressedLen bytes into dest[dOff:].

Methods inherited from class java.lang.Object

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

Field Details

MAX_DISTANCE

public static final int MAX_DISTANCE

Window size: this is the maximum supported distance between two strings so that LZ4 can replace the second one by a reference to the first one.

See Also:

• Constant Field Values

Method Details

decompress

public static int decompress(DataInput compressed,
 int decompressedLen,
 byte[] dest,
 int dOff)
                      throws IOException

Decompress at least decompressedLen bytes into dest[dOff:]. Please note that dest must be large enough to be able to hold all decompressed data (meaning that you need to know the total decompressed length). If the given bytes were compressed using a preset dictionary then the same dictionary must be provided in dest[dOff-dictLen:dOff].

Throws:

IOException

compress

public static void compress(byte[] bytes,
 int off,
 int len,
 DataOutput out,
 org.apache.lucene.util.compress.LZ4.HashTable ht)
                     throws IOException

Compress bytes[off:off+len] into out using at most 16kB of memory. ht shouldn't be shared across threads but can safely be reused.

Throws:

IOException

compressWithDictionary

public static void compressWithDictionary(byte[] bytes,
 int dictOff,
 int dictLen,
 int len,
 DataOutput out,
 org.apache.lucene.util.compress.LZ4.HashTable ht)
                                   throws IOException

Compress bytes[dictOff+dictLen:dictOff+dictLen+len] into out using at most 16kB of memory. bytes[dictOff:dictOff+dictLen] will be used as a dictionary. dictLen must not be greater than 64kB, the maximum window size.

ht shouldn't be shared across threads but can safely be reused.

Throws:

IOException