code: private void verifySum(long errPos) throws ChecksumException {
      long crc = getChecksum();
      long sumValue = sum.getValue();
      sum.reset();
      if (crc != sumValue) {
        throw new ChecksumException(
            "Checksum error: "+file+" at "+errPos, errPos);
      }
    }
docs: /* verify checksum for the chunk.
  @throws ChecksumException if there is a mismatch