it.unimi.dsi.compression

Class HuTuckerCodec

java.lang.Object

it.unimi.dsi.compression.HuTuckerCodec

All Implemented Interfaces:

Codec, PrefixCodec, Serializable

public class HuTuckerCodec
extends Object
implements PrefixCodec, Serializable

An implementation of the Hu–Tucker optimal lexicographical prefix-free code.

The familiar Huffman coding technique can be extended so to preserve the order in which symbols are given to the coder, in the sense that if j<k, then the j-th symbol will get a code lexicographically smaller than the one assigned to the k-th symbol. This result can be obtained with a small loss in code length (for more details, see the third volume of The Art of Computer Programming).

A Hu–Tucker coder is built given an array of frequencies corresponding to each symbol. Frequency 0 symbols are allowed, but they will degrade the resulting code.

The implementation of this class is rather inefficient, and the time required to build a Hu–Tucker code is quadratic in the number of symbols. An O(n log n) implementation is possible, but it requires very sophisticated data structures.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
int	size The number of symbols of this coder.

Constructor Summary

Constructors

Constructor and Description
HuTuckerCodec(int[] frequency)
HuTuckerCodec(long[] frequency)

Method Summary

Methods

Modifier and Type	Method and Description
CodeWordCoder	coder() Returns a coder for the compression technique represented by this coded.
BitVector[]	codeWords() Returns the vector of prefix-free codewords used by this prefix coder.
Decoder	decoder() Returns a decoder for the compression technique represented by this coded.
PrefixCoder	getCoder() Deprecated.
Decoder	getDecoder() Deprecated.
int	size() Returns the number of symbols handled by this codec.

Methods inherited from class java.lang.Object

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

Field Detail

size

public final int size

The number of symbols of this coder.

Constructor Detail

HuTuckerCodec

public HuTuckerCodec(int[] frequency)

HuTuckerCodec

public HuTuckerCodec(long[] frequency)

Method Detail

coder

public CodeWordCoder coder()

Description copied from interface: Codec

Returns a coder for the compression technique represented by this coded.

Specified by:

coder in interface Codec

Specified by:

coder in interface PrefixCodec

Returns:

a coder for the compression technique represented by this codec.

decoder

public Decoder decoder()

Description copied from interface: Codec

Returns a decoder for the compression technique represented by this coded.

Specified by:

decoder in interface Codec

Returns:

a decoder for the compression technique represented by this codec.

size

public int size()

Description copied from interface: Codec

Returns the number of symbols handled by this codec.

Specified by:

size in interface Codec

Returns:

the number of symbols handled by this codec.

codeWords

public BitVector[] codeWords()

Description copied from interface: PrefixCodec

Returns the vector of prefix-free codewords used by this prefix coder.

Specified by:

codeWords in interface PrefixCodec

Returns:

the vector of prefix-free codewords used by this prefix coder.

getCoder

@Deprecated
public PrefixCoder getCoder()

Deprecated.

getDecoder

@Deprecated
public Decoder getDecoder()

Deprecated.