code: private IPAddress computeMaskFromNetworkPrefix(int prefix) {
  		
  		/*
  		 * int subnet = 0; for (int i=0; i<prefix; i++) { subnet = subnet << 1; subnet += 1; }
  		 */
  		
  		StringBuilder str = new StringBuilder();
  		for (int i = 0; i < 32; i++) {
  			if (i < prefix) {
  				str.append("1");
  			} else {
  				str.append("0");
  			}
  		}
  		
  		String decimalString = toDecimalString(str.toString());
  		return new IPAddress(decimalString);
  		
  	}
docs: Convert a extended network prefix integer into an IP number.
  
  @param prefix The network prefix number.
  @return Return the IP number corresponding to the extended network
  prefix.