code: private int getIntOpRegister(final int seen) {
          if ((seen == Const.ISTORE) || (seen == Const.IINC)) {
              return getRegisterOperand();
          }
          return seen - Const.ISTORE_0;
      }
docs: fetch the register from a integer op code
  
  @param seen
  the currently parsed opcode
  
  @return the register in use