code: boolean isNormal() {
          if (intLen + offset > value.length)
              return false;
          if (intLen == 0)
              return true;
          return (value[offset] != 0);
      }
docs: Returns true iff this MutableBigInteger is in normal form. A
  MutableBigInteger is in normal form if it has no leading zeros
  after the offset, and intLen + offset <= value.length.