LFSR.java

public class LFSR {

    private boolean[] lfsr;
    private int tap;
    
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) 
    {
        LFSR lfsr = new LFSR("01101000010", 8);
        
        System.out.println("Testing step()");
        for (int i = 0; i < 10; i++) 
        {
            int bit = lfsr.step();
            System.out.println(lfsr + " " + bit);
        }
        lfsr = new LFSR("01101000010",8);
        System.out.println("\nTesting generate()");
        for (int i = 0; i < 10; i++) 
        {
            int r = lfsr.generate(5);
            System.out.println(lfsr + " " + r);
        }
    }
    
    public LFSR(String seed, int tap)
    {
        lfsr = new boolean[seed.length()];
        this.tap = (seed.length()-1)-tap;
        
        for(int i = 0; i < seed.length(); i++)
        {
            if(seed.charAt(i) == 48)
            {
                lfsr[i] = false;
            }
            else
            {
                lfsr[i] = true;
            }
        }
    }
    
    public int step()
    {
        boolean newBit = lfsr[0] ^ lfsr[tap];
        
        for(int i = 0; i < lfsr.length-1; i++)
        {
            lfsr[i] = lfsr[i+1];
        }
        lfsr[lfsr.length-1] = newBit;
        
        return newBit == false ? 0 : 1;
    }
    
    public int generate(int k)
    {
        int temp = 0;
        
        for(int i = 0; i < k; i++)
        {
            temp *= 2;
            temp += step();
        }
        
        return temp;
    }
    
    public String toString()
    {
        String representation = "";
        for(int i = 0; i < lfsr.length; i++)
        {
            representation += lfsr[i] == false ? 0 : 1;
        }
        return representation;
    }
}