org.apache.lucene.util.packed

Class 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