edu.wisc.cs.stego.lib
Class PPCTLookup

java.lang.Object
  |
  +--edu.wisc.cs.stego.lib.PPCTLookup

public class PPCTLookup

extends java.lang.Object

This class is the utility class used by PPCTEncoder and PPCTScanner. The main purpose of this class is to build a lookup table which is used for encoding and decoding the watermark. In our implementation the watermark is a very large integer represented using BigInteger. For more information on how the matrix is computed, please read Combinatorial Algorithms by Donald Kreher and Douglas Stinson

See Also:

PPCTEncoder, PPCTScanner

Constructor Summary

PPCTLookup(int catalan)
Constructor for PPCTLookup Upon successful construction, this class will contain a table built using the catalan number passed in as parameter.

Method Summary

static java.math.BigInteger	factor(int start) This method computes n!
java.math.BigInteger	lookup(int row, int column) Lookup method Given a row and column number, lookup table will return a BigInteger representing the number for that point

Methods inherited from class java.lang.Object

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

Constructor Detail

PPCTLookup

public PPCTLookup(int catalan)

Constructor for PPCTLookup Upon successful construction, this class will contain a table built using the catalan number passed in as parameter. Note that the catalan number referred here is not actually the catalan number C(n), it's n. C(n) is defined as (2n, n)/(n - 1) Techinically, the table is a matrx of size catalan X catalan * 2 However, since a large portion of the numbers in the matrix is zero (hence the matrix is sparse), we use a vector of maps to represent the matrix.

See Also:

edu.wisc.cs.stego.PPCTEncoder, edu.wisc.cs.stego.PPCTScanner

Method Detail

lookup

public java.math.BigInteger lookup(int row,
                                   int column)

Lookup method Given a row and column number, lookup table will return a BigInteger representing the number for that point

See Also:

edu.wisc.cs.stego.PPCTEncoder, edu.wisc.cs.stego.PPCTScanner

factor

public static java.math.BigInteger factor(int start)

This method computes n!