Module me.lemire.integercompression
Package me.lemire.integercompression

Class OptPFDS9

java.lang.Object
me.lemire.integercompression.OptPFDS9
All Implemented Interfaces:
IntegerCODEC, SkippableIntegerCODEC
public final class OptPFDS9 extends Object implements IntegerCODEC, SkippableIntegerCODEC
OptPFD based on Simple9 by Yan et al.

Follows:

H. Yan, S. Ding, T. Suel, Inverted index compression and query processing with optimized document ordering, in: WWW 09, 2009, pp. 401-410.

using Simple9 as the secondary coder. It encodes integers in blocks of 128 integers. For arrays containing an arbitrary number of integers, you should use it in conjunction with another CODEC: 
 IntegerCODEC ic = new Composition(new OptPFDS9(), new VariableByte()).
Note that this does not use differential coding: if you are working on sorted lists, you must compute the deltas separately. For multi-threaded applications, each thread should use its own OptPFDS9 object.
Author:
Daniel Lemire

  • Constructor Details

    • OptPFDS9

      public OptPFDS9()
      Constructor for the OptPFDS9 CODEC.

  • Method Details

    • headlessCompress

      public void headlessCompress(int[] in, IntWrapper inpos, int inlength, int[] out, IntWrapper outpos)
      Description copied from interface: SkippableIntegerCODEC
      Compress data from an array to another array. Both inpos and outpos are modified to represent how much data was read and written to. If 12 ints (inlength = 12) are compressed to 3 ints, then inpos will be incremented by 12 while outpos will be incremented by 3. We use IntWrapper to pass the values by reference. Implementation note: contrary to IntegerCODEC.compress(int[], me.lemire.integercompression.IntWrapper, int, int[], me.lemire.integercompression.IntWrapper), this may skip writing information about the number of encoded integers.
      Specified by:
      headlessCompress in interface SkippableIntegerCODEC
      Parameters:
      in - input array
      inpos - where to start reading in the array
      inlength - how many integers to compress
      out - output array
      outpos - where to write in the output array

    • headlessUncompress

      public void headlessUncompress(int[] in, IntWrapper inpos, int inlength, int[] out, IntWrapper outpos, int mynvalue)
      Description copied from interface: SkippableIntegerCODEC
      Uncompress data from an array to another array. Both inpos and outpos parameters are modified to indicate new positions after read/write.
      Specified by:
      headlessUncompress in interface SkippableIntegerCODEC
      Parameters:
      in - array containing data in compressed form
      inpos - where to start reading in the array
      inlength - length of the compressed data (ignored by some schemes)
      out - array where to write the uncompressed output
      outpos - where to start writing the uncompressed output in out
      mynvalue - number of integers we want to decode. May be less than the actual number of compressed integers

    • maxHeadlessCompressedLength

      public int maxHeadlessCompressedLength(IntWrapper compressedPositions, int inlength)
      Description copied from interface: SkippableIntegerCODEC
      Compute the maximum number of integers that might be required to store the compressed form of a given input array segment, without headers.

      This is useful to pre-allocate the output buffer before calling SkippableIntegerCODEC.headlessCompress(int[], IntWrapper, int, int[], IntWrapper).

      Specified by:
      maxHeadlessCompressedLength in interface SkippableIntegerCODEC
      Parameters:
      compressedPositions - since not all schemes compress every input integer, this parameter returns how many input integers will actually be compressed. This is useful when composing multiple schemes.
      inlength - number of integers to be compressed
      Returns:
      the maximum number of integers needed in the output array

    • compress

      public void compress(int[] in, IntWrapper inpos, int inlength, int[] out, IntWrapper outpos)
      Description copied from interface: IntegerCODEC
      Compress data from an array to another array. Both inpos and outpos are modified to represent how much data was read and written to. If 12 ints (inlength = 12) are compressed to 3 ints, then inpos will be incremented by 12 while outpos will be incremented by 3. We use IntWrapper to pass the values by reference.
      Specified by:
      compress in interface IntegerCODEC
      Parameters:
      in - input array
      inpos - where to start reading in the array
      inlength - how many integers to compress
      out - output array
      outpos - where to write in the output array

    • uncompress

      public void uncompress(int[] in, IntWrapper inpos, int inlength, int[] out, IntWrapper outpos)
      Description copied from interface: IntegerCODEC
      Uncompress data from an array to another array. Both inpos and outpos parameters are modified to indicate new positions after read/write.
      Specified by:
      uncompress in interface IntegerCODEC
      Parameters:
      in - array containing data in compressed form
      inpos - where to start reading in the array
      inlength - length of the compressed data (ignored by some schemes)
      out - array where to write the compressed output
      outpos - where to start writing the uncompressed output in out

    • toString

      public String toString()
      Overrides:
      toString in class Object