@HiveDecimalWritableVersionV2
  public int compareTo(HiveDecimal dec) {
    if (!isSet() || dec == null) {
      throw new RuntimeException("Invalid comparision operand(s)");
    }
    return fastCompareTo(dec);
  }
Allocate scratchLongs with HiveDecimal.SCRATCH_LONGS_LEN longs.
And, allocate scratch scratchBuffer with HiveDecimal.SCRATCH_BUFFER_LEN_BIG_INTEGER_BYTES bytes.
storage-api/src/java/org/apache/hadoop/hive/serde2/io/HiveDecimalWritable.java