@HiveDecimalWritableVersionV2
  public boolean mutateEnforcePrecisionScale(int precision, int scale) {
    if (!isSet) {
      return false;
    }
    isSet = fastEnforcePrecisionScale(precision, scale);
    if (!isSet) {
      fastReset();
    }
    return isSet;
  }
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