org.apache.lucene.util.encoding
Class FourFlagsIntEncoder

java.lang.Object
  org.apache.lucene.util.encoding.IntEncoder
      org.apache.lucene.util.encoding.ChunksIntEncoder
          org.apache.lucene.util.encoding.FourFlagsIntEncoder

Direct Known Subclasses:

NOnesIntEncoder

public class FourFlagsIntEncoder
extends ChunksIntEncoder

A ChunksIntEncoder which encodes values in chunks of 4. Every group starts with a single byte (called indicator) which represents 4 - 2 bit flags, where the values:

• 1, 2 or 3 mean the encoded value is '1', '2' or '3' respectively.
• 0 means the value is encoded using VInt8IntEncoder, and the encoded bytes follow the indicator.
  Since value 0 is illegal, and 1-3 are encoded in the indicator, the actual value that is encoded is value-4, which saves some more bits.

Encoding example:

• Original values: 6, 16, 5, 9, 7, 1, 11
• After sorting: 1, 5, 6, 7, 9, 11, 16
• D-Gap computing: 1, 4, 1, 1, 2, 5 (so far - done by DGapIntEncoder)
• Encoding: 1,0,1,1 as the first indicator, followed by 0 (4-4), than 2,0,0,0 as the second indicator, followed by 1 (5-4) encoded with.
• Binary encode: 01 | 01 | 00 | 01 00000000 00 | 00 | 00 | 10 00000001 (indicators are underlined).
  NOTE: the order of the values in the indicator is lsb ⇒ msb, which allows for more efficient decoding.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Field Summary

Fields inherited from class org.apache.lucene.util.encoding.ChunksIntEncoder

encodeQueue, encodeQueueSize, encoder, indicator, ordinal

Fields inherited from class org.apache.lucene.util.encoding.IntEncoder

out

Constructor Summary

FourFlagsIntEncoder()

Method Summary

IntDecoder	createMatchingDecoder() Returns an IntDecoder which matches this encoder.
void	encode(int data) Small values (<=3) are stored in the indicator while larger values are saved for later encoding in the ChunksIntEncoder.encodeQueue.
String	toString()

Methods inherited from class org.apache.lucene.util.encoding.ChunksIntEncoder

close, encodeChunk, reInit

Methods inherited from class java.lang.Object

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

Constructor Detail

FourFlagsIntEncoder

public FourFlagsIntEncoder()

Method Detail

encode

public void encode(int data)
            throws IOException

Small values (<=3) are stored in the indicator while larger values are saved for later encoding in the ChunksIntEncoder.encodeQueue. Since Vint8 will only encode values larger or equal to 4, the values saves for encoded are transformed to (value - 4).
When a chunk is ready (got 4 values), the ChunksIntEncoder.encodeChunk() takes control.

Specified by:

encode in class IntEncoder

Throws:

IOException

createMatchingDecoder

public IntDecoder createMatchingDecoder()

Description copied from class: IntEncoder

Returns an IntDecoder which matches this encoder. Every encoder must return an IntDecoder and null is not a valid value. If an encoder is just a filter, it should at least return its wrapped encoder's matching decoder.

NOTE: this method should create a new instance of the matching decoder and leave the instance sharing to the caller. Returning the same instance over and over is risky because encoders and decoders are not thread safe.

Specified by:

createMatchingDecoder in class IntEncoder

toString

public String toString()

Overrides:

toString in class Object