Package org.apache.lucene.util.packed

Class BlockPackedWriter

java.lang.Object
org.apache.lucene.util.packed.BlockPackedWriter
public final class BlockPackedWriter extends Object
A writer for large sequences of longs.

The sequence is divided into fixed-size blocks and for each block, the difference between each value and the minimum value of the block is encoded using as few bits as possible. Memory usage of this class is proportional to the block size. Each block has an overhead between 1 and 10 bytes to store the minimum value and the number of bits per value of the block.

Format:

  • <BLock>BlockCount
  • BlockCount: ⌈ ValueCount / BlockSize ⌉
  • Block: <Header, (Ints)>
  • Header: <Token, (MinValue)>
  • Token: a byte, first 7 bits are the number of bits per value (bitsPerValue). If the 8th bit is 1, then MinValue (see next) is 0 , otherwise MinValue and needs to be decoded
  • MinValue: a zigzag-encoded variable-length long whose value should be added to every int from the block to restore the original values
  • Ints: If the number of bits per value is 0, then there is nothing to decode and all ints are equal to MinValue. Otherwise: BlockSize packed ints encoded on exactly bitsPerValue bits per value. They are the subtraction of the original values and MinValue
See Also:
NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

  • Field Details

    • out

      protected DataOutput out

    • values

      protected final long[] values

    • blocks

      protected byte[] blocks

    • off

      protected int off

    • ord

      protected long ord

    • finished

      protected boolean finished

  • Constructor Details

    • BlockPackedWriter

      public BlockPackedWriter(DataOutput out, int blockSize)
      Sole constructor.
      Parameters:
      blockSize - the number of values of a single block, must be a power of 2

  • Method Details

    • flush

      protected void flush() throws IOException
      Throws:
      IOException

    • reset

      public void reset(DataOutput out)
      Reset this writer to wrap out. The block size remains unchanged.

    • add

      public void add(long l) throws IOException
      Append a new long.
      Throws:
      IOException

    • finish

      public void finish() throws IOException
      Flush all buffered data to disk. This instance is not usable anymore after this method has been called until reset(DataOutput) has been called.
      Throws:
      IOException

    • ord

      public long ord()
      Return the number of values which have been added.

    • writeValues

      protected final void writeValues(int bitsRequired) throws IOException
      Throws:
      IOException