@HiveDecimalWritableVersionV2
  public boolean serializationUtilsRead(
      InputStream inputStream, int scale,
      byte[] scratchBytes)
          throws IOException {
    fastReset();
    isSet =
        fastSerializationUtilsRead(
            inputStream,
            scale,
            scratchBytes);
    return isSet;
  }
See the comments for HiveDecimal.serializationUtilsRead.
storage-api/src/java/org/apache/hadoop/hive/serde2/io/HiveDecimalWritable.java