@HiveDecimalVersionV2
  public String toString(
      byte[] scratchBuffer) {
    if (fastSerializationScale() != -1) {

      // Use the serialization scale and format the string with trailing zeroes (or
      // round the decimal) if necessary.
      return
          fastToFormatString(
              fastSerializationScale(),
              scratchBuffer);
    } else {
      return
          fastToString(scratchBuffer);
    }
  }
Return a string representation of the decimal.
<p>
It is the equivalent of calling bigDecimalValue().toPlainString -- it does not add exponent
notation -- but is much faster.
<p>
NOTE: If setScale(int serializationScale) was used to create the decimal object, then trailing
fractional digits will be added to display to the serializationScale.  Or, the display may
get rounded.  See the comments for that method.
storage-api/src/java/org/apache/hadoop/hive/common/type/HiveDecimal.java