@Override
  protected void func(TimestampColumnVector outV, DecimalColumnVector inV,  int i) {
    Timestamp timestamp =
        TimestampUtils.decimalToTimestamp(
            inV.vector[i],
            scratchHiveDecimalWritable1, scratchHiveDecimalWritable2);
    outV.set(i, timestamp);
  }
Type cast decimal to timestamp. The decimal value is interpreted
as NNNN.DDDDDDDDD where NNNN is a number of seconds and DDDDDDDDD
is a number of nano-seconds.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/CastDecimalToTimestamp.java