Package org.apache.iotdb.tsfile.encoding.encoder

Class 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.

    • Field Detail

      • out

        protected java.io.ByteArrayOutputStream out

      • blockSize

        protected int blockSize

      • encodingBlockBuffer

        protected byte[] encodingBlockBuffer

      • writeIndex

        protected int writeIndex

      • writeWidth

        protected int writeWidth

    • Constructor Detail

      • DeltaBinaryEncoder

        protected 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 java.io.IOException
        Throws:
        java.io.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​(java.io.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