What is a running CRC?

Question

I have searched and am not able to find information on what it is and how it is computed.

Answer 1

Well, basically it's just a CRC. The word running would mean that you are supposed to calculate it on-the-fly, as the data is incoming, or that you are doing a cumulative calculation (which is the way CRC is implemented).

You have a good example:

  # Or you can compute the running CRC:
  $crc = 0;
  $crc = Archive::Zip::computeCRC32( 'abcdef', $crc );
  $crc = Archive::Zip::computeCRC32( 'ghijkl', $crc );

Note how the $crc variable is set to 0 at the beginning, and the updated twice. The algorithm for CRC calculation uses the previously calculated CRC value and updates it. That is why it is sometimes called running CRC.

From your code I presume you already have an implementation, if not, simply google for CRC32.

Answer 2

I have no idea why the question has been negative voted. Is it not clear and programming related? Or should I have asked:

# Or you can compute the running CRC:
$crc = 0;
$crc = Archive::Zip::computeCRC32( 'abcdef', $crc );
$crc = Archive::Zip::computeCRC32( 'ghijkl', $crc );

What exactly happens here?