Package org.apache.lucene.util.encoding
Class FourFlagsIntEncoder
- java.lang.Object
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- org.apache.lucene.util.encoding.IntEncoder
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- org.apache.lucene.util.encoding.ChunksIntEncoder
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- org.apache.lucene.util.encoding.FourFlagsIntEncoder
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- Direct Known Subclasses:
NOnesIntEncoder
public class FourFlagsIntEncoder extends ChunksIntEncoder
AChunksIntEncoder
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 isvalue-4
, which saves some more bits.
- 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.
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Field Summary
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Fields inherited from class org.apache.lucene.util.encoding.ChunksIntEncoder
encodeQueue, encodeQueueSize, encoder, indicator, ordinal
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Fields inherited from class org.apache.lucene.util.encoding.IntEncoder
out
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Constructor Summary
Constructors Constructor Description FourFlagsIntEncoder()
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description IntDecoder
createMatchingDecoder()
Returns anIntDecoder
which matches this encoder.void
encode(int data)
Small values (<=3) are stored in theindicator
while larger values are saved for later encoding in theChunksIntEncoder.encodeQueue
.String
toString()
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Methods inherited from class org.apache.lucene.util.encoding.ChunksIntEncoder
close, encodeChunk, reInit
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Method Detail
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encode
public void encode(int data) throws IOException
Small values (<=3) are stored in theindicator
while larger values are saved for later encoding in theChunksIntEncoder.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), theChunksIntEncoder.encodeChunk()
takes control.- Specified by:
encode
in classIntEncoder
- Throws:
IOException
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createMatchingDecoder
public IntDecoder createMatchingDecoder()
Description copied from class:IntEncoder
Returns anIntDecoder
which matches this encoder. Every encoder must return anIntDecoder
andnull
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 classIntEncoder
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