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:
  - `BlockPackedReaderIterator`
NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected byte[]`
  `blocks`
  `protected boolean`
  `finished`
  `protected int`
  `off`
  `protected long`
  `ord`
  `protected DataOutput`
  `out`
  `protected final long[]`
  `values`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `BlockPackedWriter(DataOutput out, int blockSize)`
  Sole constructor.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `add(long l)`
  Append a new long.
  `void`
  `finish()`
  Flush all buffered data to disk.
  `protected void`
  `flush()`
  `long`
  `ord()`
  Return the number of values which have been added.
  `void`
  `reset(DataOutput out)`
  Reset this writer to wrap `out`.
  `protected final void`
  `writeValues(int bitsRequired)`

  ### Methods inherited from class java.lang.Object

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

- ## 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`