anon.mixminion.fec
Class Pure16Code

java.lang.Object
  anon.mixminion.fec.FECCode
      anon.mixminion.fec.PureCode
          anon.mixminion.fec.Pure16Code

public class Pure16Code
extends PureCode

This class, along with FECMath, provides the implementation of the pure Java 16 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), JAP-Team -- made some changes

Field Summary

protected static FECMath

fecMath

Fields inherited from class anon.mixminion.fec.PureCode

encMatrix, FEC_MAGIC

Fields inherited from class anon.mixminion.fec.FECCode

k, n

Constructor Summary

Pure16Code(int k, int n)
Notes about large N support: you can just generate the top k*k vandermonde matrix, call it V, then invert it, then when you have k blocks generate a matrix M with the k rows you need and E = M* V^{-1} is the encoding matrix for the systematic code which you then need to invert to perform the decoding.

Method Summary

void	decode(byte[][] pkts, int[] pktsOff, int[] index, int packetLength, boolean inOrder) This method takes an array of encoded packets and decodes them.
protected char[][]	decode(char[][] pkts, int[] pktsOff, int[] index, int numChars)
void	encode(byte[][] src, int[] srcOff, byte[][] repair, int[] repairOff, int[] index, int packetLength) 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(char[][] src, int[] srcOff, char[] repair, int repairOff, int index, int numChars) ASSERT: index >= k && index < n
java.lang.String	toString()

Methods inherited from class anon.mixminion.fec.PureCode

encode

Methods inherited from class anon.mixminion.fec.FECCode

shuffle

Methods inherited from class java.lang.Object

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

Field Detail

fecMath

protected static final FECMath fecMath

Constructor Detail

Pure16Code

public Pure16Code(int k,
                  int n)

Notes about large N support: you can just generate the top k*k vandermonde matrix, call it V, then invert it, then when you have k blocks generate a matrix M with the k rows you need and E = M* V^{-1} is the encoding matrix for the systematic code which you then need to invert to perform the decoding. Probably there is a fast way to invert E given that M is also a vandermonde matrix so it is "easy" to compute M^{-1}

Method Detail

encode

public void encode(byte[][] src,
                   int[] srcOff,
                   byte[][] repair,
                   int[] repairOff,
                   int[] index,
                   int packetLength)

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".

Overrides:

encode in class PureCode

Parameters:

src - An array of k byte[]'s that contain the source packets to be encoded. Often these byte[]'s are actually references to a single byte[] that contains the entire source block, then you must simply vary the srcOff's to pass it in in this fashion. src[0] will point to the 1st packet, src[1] to the second, etc.

srcOff - An array of integers which specifies the offset of each each packet within its associated byte[].

repair - Much like src, variable points to a number of buffers to which the encoded repair packets will be written. This array should be the same length as repairOff and index.

repairOff - This is the repair analog to srcOff.

index - This int[] specifies the indexes of the packets to be encoded and written to repair. These indexes must be between 0..n (should probably be k..n, because encoding < k is a NOP)

packetLength - the packetLength in bytes. All of the buffers in src and repair are assumed to be this long.

encode

protected void encode(char[][] src,
                      int[] srcOff,
                      char[] repair,
                      int repairOff,
                      int index,
                      int numChars)

ASSERT: index >= k && index < n

decode

public void decode(byte[][] pkts,
                   int[] pktsOff,
                   int[] index,
                   int packetLength,
                   boolean inOrder)

Description copied from class: FECCode

This method takes an array of encoded packets and decodes them. Before the packets are decoded, they are shuffled so that packets that are original source packets (index < k) are positioned so that their index within the byte[][] is the same as their packet index. If the shuffled flag is set to true then it is assumed that the packets are already in the proper order. If not then they will have the references of the byte[]'s shuffled within the byte[][]. No data will be copied, only references swapped. This means that if the byte[][] is wrapping an underlying byte[] then the shuffling proceedure may bring the byte[][] out of sync with the underlying data structure. From an SPI perspective this means that the implementation is expected to follow the exact same behavior as the shuffle() method in this class which means that you should simply call shuffle() if the flag is false.

Overrides:

decode in class PureCode

Parameters:

pkts - An array of k byte[]'s that contain the repair packets to be decoded. The decoding proceedure will copy the decoded data into the byte[]'s that are provided and will place them in order within the byte[][]. If the byte[][] is already properly shuffled then the byte[]'s will not be moved around in the byte[][].

pktsOff - An array of integers which specifies the offset of each each packet within its associated byte[].

index - This int[] specifies the indexes of the packets to be decoded. These indexes must be between 0..n

packetLength - the packetLength in bytes. All of the buffers in pkts are assumed to be this long.

decode

protected char[][] decode(char[][] pkts,
                          int[] pktsOff,
                          int[] index,
                          int numChars)

toString

public java.lang.String toString()

Overrides:

toString in class PureCode