@HiveDecimalVersionV1
  @Override
  public int hashCode() {
    return fastHashCode();
  }
This is returns original hash code as returned by HiveDecimalV1.
<p>
We need this when the HiveDecimalV1 hash code has been exposed and and written or affected
how data is written.
<p>
This method supports compatibility.
<p>
Examples: bucketing, Hive hash() function, and Hive statistics.
<p>
NOTE: It is necessary to create a BigDecimal object and use its hash code, so this method is
      slow.
storage-api/src/java/org/apache/hadoop/hive/common/type/HiveDecimal.java