private Register SelectRegister() {
        
        Register Rselected;
		
         switch (getRF().Index) {
            case 0:
                Rselected = getGPR0();
                break;
            case 1:
                Rselected = getGPR1();
                break;
            case 2:
                Rselected = getGPR2();
                break;   
             case 3:
                Rselected = getGPR3();
                break;
             default:
                 Rselected = null;
                 break;
         }
         
         return Rselected;
         
 }