me.lemire.integercompression
Class OptPFD

java.lang.Object
  me.lemire.integercompression.OptPFD

All Implemented Interfaces:

IntegerCODEC

public final class OptPFD
extends Object
implements IntegerCODEC

OptPFD: fast patching scheme 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 Simple16 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 OptPFD(), new VariableByte()).

Note that this does not use differential coding: if you are working on sorted lists, you must compute the deltas separately. (Yes, this is true even though the "D" at the end of the name probably stands for delta.) For multi-threaded applications, each thread should use its own OptPFD object.

Author:

Daniel Lemire

Field Summary

protected static int[]	bits
protected static int[]	invbits

Constructor Summary

OptPFD()
Constructor for the OptPFD CODEC.

Method Summary

void	compress(int[] in, IntWrapper inpos, int inlength, int[] out, IntWrapper outpos) Compress data from an array to another array.
String	toString()
void	uncompress(int[] in, IntWrapper inpos, int inlength, int[] out, IntWrapper outpos) Uncompress data from an array to another array.

Methods inherited from class java.lang.Object

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

Field Detail

bits

protected static final int[] bits

invbits

protected static final int[] invbits

Constructor Detail

OptPFD

public OptPFD()

Constructor for the OptPFD CODEC.

Method Detail

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 - location in the input 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 write the compressed output in out

toString

public String toString()

Overrides:

toString in class Object