Package me.lemire.integercompression

Class OptPFD

java.lang.Object

me.lemire.integercompression.OptPFD

All Implemented Interfaces:

IntegerCODEC, SkippableIntegerCODEC

public final class OptPFD
extends Object
implements IntegerCODEC, SkippableIntegerCODEC

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

Constructor Summary

Constructors

Constructor	Description
OptPFD()	Constructor for the OptPFD CODEC.

Method Summary

Modifier and Type	Method	Description
void	compress(int[] in, IntWrapper inpos, int inlength, int[] out, IntWrapper outpos)	Compress data from an array to another array.
void	headlessCompress(int[] in, IntWrapper inpos, int inlength, int[] out, IntWrapper outpos)	Compress data from an array to another array.
void	headlessUncompress(int[] in, IntWrapper inpos, int inlength, int[] out, IntWrapper outpos, int mynvalue)	Uncompress 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

Constructor Details

OptPFD

public OptPFD()

Constructor for the OptPFD 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

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