title: Why we need to invert crc? In which cases we need to do this?
body: <p>Why we need to invert crc? In which cases we need to do this? (invert mean <code>crc = ~crc</code>)</p>
  
  <p>Is it defence from zero cases (when whole message is consists of zeros)? </p>
  
  <p>How it helps in this case?</p>