PureCode.java

package com.onionnetworks.fec;

import com.onionnetworks.util.Util;
import com.onionnetworks.util.Buffer;
/**
 * This class, along with FECMath, provides the implementation of the pure
 * Java 8 bit FEC codes.  This is heavily dervied from Luigi Rizzos original
 * C implementation.  See the file "LICENSE" along with this distribution for
 * additional copyright information.
 *
 * (c) Copyright 2001 Onion Networks
 * (c) Copyright 2000 OpenCola
 *
 * @author Justin F. Chapweske (justin@chapweske.com)
 */
public class PureCode extends FECCode {

    // Keeping this around because it amuses me.
    public static final int FEC_MAGIC = 0xFECC0DEC;
    protected static final FECMath fecMath = new FECMath(8);
    protected char[] encMatrix;
    
    //create a new encoder. This contains n,k and the encoding matrix.
    public PureCode(int k, int n) {
        this(k,n,fecMath.createEncodeMatrix(k,n));
    }

    public PureCode(int k, int n, char[] encMatrix) {
        super(k,n);
        this.encMatrix = encMatrix;
    }

    /**
     * encode accepts as input pointers to n data packets of size sz,
     * and produces as output a packet pointed to by fec, computed
     * with index "index".
     */
    protected void encode(byte[][] src, int[] srcOff, byte[][] repair, 
                          int[] repairOff, int[] index, int packetLength) {
        for (int i=0;i<repair.length;i++) {
            encode(src,srcOff,repair[i],repairOff[i],index[i],packetLength);
        }
    }

    protected void encode(byte[][] src, int[] srcOff, byte[] repair, 
                          int repairOff, int index, int packetLength) {
        // *remember* indices start at 0, k starts at 1.
        if (index < k) { // < k, systematic so direct copy.
            System.arraycopy(src[index],srcOff[index],repair,repairOff,
                             packetLength);
        } else { // index >= k && index < n
            int pos = index*k;
            Util.bzero(repair,repairOff,packetLength);
            for (int i=0; i<k ; i++) {
                fecMath.addMul(repair,repairOff,src[i],srcOff[i],
                                   (byte) encMatrix[pos+i],packetLength);
            }
        } 
    }
    
    protected void decode(byte[][] pkts, int[] pktsOff, int[] index, 
                          int packetLength, boolean shuffled) {                
        // This may be the second time shuffle has been called, if so
        // this is ok because it will quickly determine that things are in
        // order.  The previous shuffles may have been necessary to keep
        // another data structure in sync with the byte[]'s
        if (!shuffled) {
            shuffle(pkts, pktsOff, index, k);
        }

        char[] decMatrix = fecMath.createDecodeMatrix(encMatrix,index,k,n);
        
        // do the actual decoding..
        byte[][] tmpPkts = new byte[k][];
        for (int row=0; row<k; row++) {
            if (index[row] >= k) {
                tmpPkts[row] = new byte[packetLength];
                for (int col=0 ; col<k ; col++) {
                    fecMath.addMul(tmpPkts[row],0,pkts[col],pktsOff[col], 
                                   (byte) decMatrix[row*k + col],
                                   packetLength);
                }
            }
        }

        // move pkts to their final destination
        for (int row=0;row < k;row++) {
            if (index[row] >= k) { // only copy those actually decoded.
                System.arraycopy(tmpPkts[row],0, pkts[row],pktsOff[row],
                                 packetLength);
                index[row] = row;
            }
        }
    }
    
    public String toString() {
        return new String("PureCode[k="+k+",n="+n+"]");
    }
}