sign « biginteger « Java Data Type Q&A

1. why is a minus sign prepended to my biginteger?    stackoverflow.com

package ewa;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.math.BigInteger;
/**
 *
 * @author Lotus
 */
public class md5Hash {

    public static void main(String[] args) throws NoSuchAlgorithmException {
     ...

2. BigInteger unsigned left or right shift    stackoverflow.com

I am reimplementing a function using BigInteger in place in int. Now there is step

h = n >>> log2n--