org.apache.iotdb.tsfile.encoding.encoder

Class DeltaBinaryEncoder

java.lang.Object

org.apache.iotdb.tsfile.encoding.encoder.Encoder

org.apache.iotdb.tsfile.encoding.encoder.DeltaBinaryEncoder

Direct Known Subclasses:

DeltaBinaryEncoder.IntDeltaEncoder, DeltaBinaryEncoder.LongDeltaEncoder

public abstract class DeltaBinaryEncoder
extends Encoder

DeltaBinaryEncoder is a encoder for compressing data in type of integer and long. We adapt a hypothesis that contiguous data points have similar values. Thus the difference value of two adjacent points is smaller than those two point values. One integer in java takes 32-bits. If a positive number is less than 2^m, the bits of this integer which index from m to 31 are all 0. Given an array which length is n, if all values in input data array are all positive and less than 2^m, we need actually m*n, but not 32*n bits to store the array.

DeltaBinaryEncoder calculates difference between two adjacent points and record the minimum of those difference values firstly. Then it saves two_diff value that difference minus minimum of them, to make sure all two_diff values are positive. Then it statistics the longest bit length m it takes for each two_diff value, which means the bit length that maximum two_diff value takes. Only the low m bits are saved into result byte array for all two_diff values.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	DeltaBinaryEncoder.IntDeltaEncoder
static class	DeltaBinaryEncoder.LongDeltaEncoder

Field Summary

Fields

Modifier and Type	Field and Description
protected static int	BLOCK_DEFAULT_SIZE
protected int	blockSize
protected byte[]	encodingBlockBuffer
protected ByteArrayOutputStream	out
protected int	writeIndex
protected int	writeWidth

Fields inherited from class org.apache.iotdb.tsfile.encoding.encoder.Encoder

MAX_POINT_NUMBER, MAX_STRING_LENGTH

Constructor Summary

Constructors

Constructor and Description
DeltaBinaryEncoder(int size) constructor of DeltaBinaryEncoder.

Method Summary

Modifier and Type	Method and Description
protected abstract void	calcTwoDiff(int i)
protected abstract int	calculateBitWidthsForDeltaBlockBuffer()
void	flush(ByteArrayOutputStream out) calling this method to flush all values which haven't encoded to result byte array.
protected abstract void	reset()
protected abstract void	writeHeader()
protected abstract void	writeValueToBytes(int i)

Methods inherited from class org.apache.iotdb.tsfile.encoding.encoder.Encoder

encode, encode, encode, encode, encode, encode, encode, encode, getMaxByteSize, getOneItemMaxSize, getType, setType

Methods inherited from class java.lang.Object

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

Field Detail

BLOCK_DEFAULT_SIZE

protected static final int BLOCK_DEFAULT_SIZE

See Also:

Constant Field Values

out

protected ByteArrayOutputStream out

blockSize

protected int blockSize

encodingBlockBuffer

protected byte[] encodingBlockBuffer

writeIndex

protected int writeIndex

writeWidth

protected int writeWidth

Constructor Detail

DeltaBinaryEncoder

public DeltaBinaryEncoder(int size)

constructor of DeltaBinaryEncoder.

Parameters:

size - - the number how many numbers to be packed into a block.

Method Detail

writeHeader

protected abstract void writeHeader()
                             throws IOException

Throws:

IOException

writeValueToBytes

protected abstract void writeValueToBytes(int i)

calcTwoDiff

protected abstract void calcTwoDiff(int i)

reset

protected abstract void reset()

calculateBitWidthsForDeltaBlockBuffer

protected abstract int calculateBitWidthsForDeltaBlockBuffer()

flush

public void flush(ByteArrayOutputStream out)

calling this method to flush all values which haven't encoded to result byte array.

Specified by:

flush in class Encoder

Parameters:

out - - ByteArrayOutputStream