public void set(int elementNum, HiveDecimalWritable writable) {
    scratchHiveDecWritable.set(writable);
    scratchHiveDecWritable.mutateEnforcePrecisionScale(precision, scale);
    if (!scratchHiveDecWritable.isSet()) {
      noNulls = false;
      isNull[elementNum] = true;
    } else {
      vector[elementNum] = scratchHiveDecWritable.serialize64(scale);
    }
  }
Set a Decimal64 field from a HiveDecimalWritable.

This is a FAST version that assumes the caller has checked to make sure the writable
is not null and elementNum is correctly adjusted for isRepeating.  And, that the isNull entry
has been set.

We will check for precision/scale range, so the entry's NULL may get set.
Otherwise, only the output entry fields will be set by this method.

@param elementNum
@param writable
storage-api/src/java/org/apache/hadoop/hive/ql/exec/vector/Decimal64ColumnVector.java