it.unimi.dsi.bits

Class PrefixCoderTransformationStrategy

java.lang.Object

it.unimi.dsi.bits.PrefixCoderTransformationStrategy

All Implemented Interfaces:

TransformationStrategy<CharSequence>, Serializable

Direct Known Subclasses:

HuTuckerTransformationStrategy

public class PrefixCoderTransformationStrategy
extends Object
implements TransformationStrategy<CharSequence>

A transformation strategy mapping strings using a prefix-free encoder.

The actual encoding must be provided via a map from characters to symbols, and a set of codewords. The default return value of the map will be used for unknown characters.

This strategy creates a new LongArrayBitVector each time toBitVector(CharSequence) is invoked.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected Char2IntOpenHashMap	char2symbol
protected BitVector[]	codeWord
protected boolean	prefixFree

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	PrefixCoderTransformationStrategy(BitVector[] codeWord, Char2IntOpenHashMap char2symbol, boolean prefixFree)
	PrefixCoderTransformationStrategy(PrefixCoder coder, Char2IntOpenHashMap char2symbol, boolean prefixFree) Create a new transformation strategy based on a prefix-free coder.
protected	PrefixCoderTransformationStrategy(PrefixCoderTransformationStrategy transformationStrategy)

Method Summary

Modifier and Type	Method and Description
PrefixCoderTransformationStrategy	copy() Returns a copy of this transformation strategy.
long	length(CharSequence s) Returns the length of the bit vector that would be computed by TransformationStrategy.toBitVector(Object).
long	numBits() The (approximate) number of bits occupied by this transformation.
LongArrayBitVector	toBitVector(CharSequence s) Returns a bit vector representation of the given object.

Methods inherited from class java.lang.Object

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

Field Detail

codeWord

protected final BitVector[] codeWord

char2symbol

protected final Char2IntOpenHashMap char2symbol

prefixFree

protected final boolean prefixFree

Constructor Detail

PrefixCoderTransformationStrategy

public PrefixCoderTransformationStrategy(PrefixCoder coder,
                                         Char2IntOpenHashMap char2symbol,
                                         boolean prefixFree)

Create a new transformation strategy based on a prefix-free coder.

Parameters:

coder - a prefix-free coder.

char2symbol - a map from character to symbols (the default returned value will be used for unknown symbols).

prefixFree - whether it is required that the resulting bit vectors are prefix-free: in this case, symbol 0 will be appended to each string, and will not be allowed to appear in any string.

PrefixCoderTransformationStrategy

protected PrefixCoderTransformationStrategy(PrefixCoderTransformationStrategy transformationStrategy)

PrefixCoderTransformationStrategy

protected PrefixCoderTransformationStrategy(BitVector[] codeWord,
                                            Char2IntOpenHashMap char2symbol,
                                            boolean prefixFree)

Method Detail

toBitVector

public LongArrayBitVector toBitVector(CharSequence s)

Description copied from interface: TransformationStrategy

Returns a bit vector representation of the given object.

Specified by:

toBitVector in interface TransformationStrategy<CharSequence>

Parameters:

s - the object to be turned into a bit-vector representation.

Returns:

a bit-vector representation of object.

length

public long length(CharSequence s)

Description copied from interface: TransformationStrategy

Returns the length of the bit vector that would be computed by TransformationStrategy.toBitVector(Object).

The raison d'être of this method is that it is often easy to know the length of the representation without actually computing the representation.

Specified by:

length in interface TransformationStrategy<CharSequence>

Parameters:

s - the object whose representation length is to be known.

Returns:

the length of the bit-vector representation of object (the one that would be returned by TransformationStrategy.toBitVector(Object)).

numBits

public long numBits()

Description copied from interface: TransformationStrategy

The (approximate) number of bits occupied by this transformation.

Specified by:

numBits in interface TransformationStrategy<CharSequence>

Returns:

the (approximate) number of bits occupied by this transformation.

copy

public PrefixCoderTransformationStrategy copy()

Description copied from interface: TransformationStrategy

Returns a copy of this transformation strategy.

Specified by:

copy in interface TransformationStrategy<CharSequence>

Returns:

a copy of this transformation strategy.