Package me.lemire.integercompression

Interface SkippableIntegerCODEC

All Known Implementing Classes:

BinaryPacking, FastPFOR, FastPFOR128, GroupSimple9, JustCopy, Kamikaze, NewPFD, NewPFDS16, NewPFDS9, OptPFD, OptPFDS16, OptPFDS9, Simple16, Simple9, SkippableComposition, VariableByte

public interface SkippableIntegerCODEC

Interface describing a standard CODEC to compress integers. This is a variation on the IntegerCODEC interface meant to be used for random access (i.e., given a large array, you can segment it and decode just the subarray you need). The main difference is that you must specify the number of integers you wish to uncompress. This information should be stored elsewhere. This interface was designed by the Terrier team for their search engine.

Author:

Daniel Lemire

Method Summary

Modifier and Type	Method	Description
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 num)	Uncompress data from an array to another array.

Method Details

headlessCompress

void headlessCompress(int[] in,
 IntWrapper inpos,
 int inlength,
 int[] out,
 IntWrapper outpos)

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.

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

void headlessUncompress(int[] in,
 IntWrapper inpos,
 int inlength,
 int[] out,
 IntWrapper outpos,
 int num)

Uncompress data from an array to another array. Both inpos and outpos parameters are modified to indicate new positions after read/write.

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

num - number of integers we want to decode. May be less than the actual number of compressed integers