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`, `BlockPackedReader`
  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 and Description
    --- | ---
    `protected byte[]` | `blocks`
    `protected boolean` | `finished`
    `protected int` | `off`
    `protected long` | `ord`
    `protected DataOutput` | `out`
    `protected long[]` | `values`

  - ### Constructor Summary

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

  - ### Method Summary

    Methods
    Modifier and Type | Method and 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 void` | `writeValues(int bitsRequired)`

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

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

- - ### Field Detail

    - #### 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 Detail

    - #### 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 Detail

    - #### 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`

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