Exception in ECC

Question

I am trying to implement ECC : Error correcting Code / reed-solomon. I try to apply it over a file but each split at the time. My problem is that it works for the first splits but then I get this error :

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 8217
at package_name.GF28.mult(GF28.java:73)
at package_name.Encoder.encode(Encoder.java:36)
at package_name.ErrorCodesMain.Ecc(ErrorCodesMain.java:27)

This exception occurs after encoding the first three splits, each split having 72bytes. Any suggestion of what can be wrong?

I tried to narrow where the problem comes from and I see that it comes from the class constructing the Galois Field: Here is where the bug happens:

public GF28 mult(char b) {
    if (!multsDone[val][b]) {
        mults[val][b] = mult(val, b);
        mults[b][val] = mults[val][b];
        multsDone[val][b] = true;
        multsDone[b][val] = true;}

    return new GF28(mults[val][b]);
}

and here is the whole class code

package package_name;
import java.util.*;

public class GF28 {
public static char[][] adds;
public static char[][] mults;
public static char[] inverse;
public static boolean[][] addsDone;
public static boolean[][] multsDone;
public static boolean[] inverseDone;

public static final char PX = (char) 0x11B;

public static void init() {
    int max = 1 << 8;
    adds = new char[max][max];
    mults = new char[max][max];
    addsDone = new boolean[max][max];
    multsDone = new boolean[max][max];
    inverse = new char[max];
    inverseDone = new boolean[max];
    for (int i = 0; i < adds.length; i++) {
        inverse[i] = 0;
        inverseDone[i] = false;
        for (int j = 0; j < adds[0].length; j++) {
            adds[i][j] = 0;
            mults[i][j] = 0;
            addsDone[i][j] = false;
            multsDone[i][j] = false;
        }
    }
}

public static char add(char a, char b) {
    return (char) (a ^ b);
}

public static char mult(char a, char b) {
    int p = a;
    int r = 0;
    while (b != 0) {
        if ((b & 1) == 1)
            r = r ^ p;
        b = (char) (b >>> 1);
        p = p << 1;
        if ((p & 0x100) == 0x100)
            p = p ^ PX;
    }
    return (char) r;
}

char val;

public GF28(char val) {
    this.val = val;
}

public GF28 add(char b) {
    if (!addsDone[val][b]) {
        adds[val][b] = add(val, b);
        adds[b][val] = adds[val][b];
        addsDone[val][b] = true;
        addsDone[b][val] = true;
    }
    return new GF28(adds[val][b]);
}

public GF28 add(GF28 b) {
    return add(b.val);
}

public GF28 mult(char b) {
    if (!multsDone[val][b]) {
        mults[val][b] = mult(val, b);
        mults[b][val] = mults[val][b];
        multsDone[val][b] = true;
        multsDone[b][val] = true;}

    return new GF28(mults[val][b]);
}

public GF28 mult(GF28 b) {
    return mult(b.val);
}

public GF28 getInverse() {
    return inverse(val);
}

public static GF28 inverse(char a) {
    if (!inverseDone[a]) {
        GF28 ga = new GF28(a);
        for (char i = 0; i < (1 << 8); i++) {
            if (ga.mult(i).val == 1) {
                inverseDone[a] = true;
                inverseDone[i] = true;
                inverse[a] = i;
                inverse[i] = a;
                break;
            }
        }
    }
    return new GF28(inverse[a]);
}

public static String getBinaryString(char c) {
    String s = "";
    for (int i = 0; i < 8; i++) {
        s = (c % 2) + s;
        c = (char) (c >> 1);
    }
    return "0b" + s;
}

public static ArrayList<Integer> findGenerators() {
    ArrayList<Integer> gs = new ArrayList<Integer>();
    for (int j = 1; j < 1 << 8; j++) {
        GF28 gz = new GF28((char) j);
        HashSet<Character> hs = new HashSet<Character>();
        hs.add(gz.val);
        for (int i = 2; i <= 1 << 8; i++) {
            gz = gz.mult((char) j);
            hs.add(gz.val);
        }
        if (hs.size() == 255)
            gs.add(j);
    }
    return gs;
}

}