title: CRC64 file checksum PHP implementation
body: <p>I need to get CRC64 checksum of files using PHP.</p>
  
  <p>With this code</p>
  
  <pre><code>file_put_contents('example.txt', 'just an example');
  
  echo hash_file('crc32', 'example.txt');
  </code></pre>
  
  <p>I get CRC32 checksum "c8c429fe";</p>
  
  <p>But I need to get a checksum using CRC64 algorithm (</p>
  
  <p><img src="https://i.stack.imgur.com/otBup.png" alt="enter image description here">)</p>
  
  <p>I took it from here: <a href="http://en.wikipedia.org/wiki/Cyclic_redundancy_check" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Cyclic_redundancy_check</a> </p>
  
  <p>How can I implement this hashing algorithm in PHP?</p>