@HiveDecimalWritableVersionV2
  public void setFromLong(long longValue) {
    fastReset();
    fastSetFromLong(longValue);
    isSet = true;
  }
Set a decimal writable's value to a long's value with scale 0.
<p>
Afterwards, the isSet() method will return true since all long values fit in a decimal.
storage-api/src/java/org/apache/hadoop/hive/serde2/io/HiveDecimalWritable.java