@Override
  public String toString() {
    return toFormalString() + "(Decimal128: scale=" + scale + ", signum="
        + signum + ", BigDecimal.toString=" + toBigDecimal().toString()
        + ", unscaledValue=[" + unscaledValue.toString() + "])";
  }
Returns the formal string representation of this value. Unlike the debug
string returned by {@link #toString()}, this method returns a string that
can be used to re-construct this object. Remember, toString() is only for
debugging.

@return string representation of this value
common/src/java/org/apache/hadoop/hive/common/type/Decimal128.java