Reed–Solomon error correction in java, providing RS(255,223) encode and decode method.
#Usage encode the string before net transmission or local storage:
RSEncoder encoder=new RSEncoder();
byte[] bytes=encoder.encode(string);
decode while receiving from network or reading from the disk
String result=decoder.decode(receive);
#Example
public static void simulateTransmission(String message){
//encode
System.out.println("String ready to translate：");
System.out.println(message);
System.out.println("--------------------------");
RSEncoder encoder=new RSEncoder();
byte[] bytes=encoder.encode(message);
RSDecoder decoder=new RSDecoder();
//modify several bytes to simulate errors in transmission
byte[] receive=bytes;
receive[0]='a';
receive[300]='a';
receive[301]='b';
//decode
String result=decoder.decode(receive);
System.out.println("--------------------------");
System.out.println("String after error correction： ");
System.out.println(result);
System.out.println("--------------------------");
System.out.println("Is result the same as message？： "+message.equals(result));
}
#Document
- Class RSEncoder
byte[] encode(String message)
Encode the given string with RS(255,223).Return encoded byte array.
First，invoke enlargeMessage() to make sure message string can be divided into several encoding unit.Then,for each encoding unit,invoke doEncode().At last,merge the codeword polynomial ,and turn it to byte array.
Polynomial doEncode(String unit)
Conduct encoding for each encoding unit.Return codeword polynomial.The length of an encoding unit is 223.After encoding,32 byte redundancy is added into the unit.
String enlargeMessage(String message)
Enlarge message string to integer multiples of 223, by padding zeros at the end of string.
- Class RSDecoder
String decode(byte[] receive)
Decode the given byte array ,correct the error and return raw stirng.
For each 255-length decoding unit,invoke the doDecode() and use StringBuffer to store the decoded string.After that,turn StirngBuffer to string,and trim the string(Because raw string has been padded by zeros after encoding).
String doDecode(byte[] receive)
Conduct decoding for each decoding unit.Return decoded string.
Procedure:
(1)calSyndromes(Polynomial receive)：Calculate syndromes polynomial.
(2)calBerlekampMassey(Polynomial s):Run BerlekampMassey algorithm,input syndromes polynomial and return array of sigma and omega.
(3)chienSearch(Polynomial sigma):Input error-locator polynomial--sigma,return the roots of sigma.
(4)forney():Input error-value polynomial--omega and the corresponding error location,return the coefficient of error polynomial.
(5)generate error polynomial,codeword = receive - error polynomial.