Unsigned value handling in CRC calculator

[sparkpunkd]

I am writing a 100% Javascript MPEG-TS library for Node-JS.

FYI, I was following the patterns in your CRC code and found an issues where in certain cases the CRC values could go negative. This is caused by the way Javascript treats unsigned integers when bit shifting. My altered version of the CRC calculator uses the >>> 0 operator to force treatment as unsigned and that seems to fix the issue. For example:

function crc (b) => {
  var crc = 0xffffffff;
  for (var i = 0; i < b.length; ++i) {
    var tableIndex = ((crc >>> 24) ^ b[i]) & 0xff;
    crc = ((crcTable[tableIndex] ^ (crc << 8)) & 0xffffffff) >>> 0;
  }
  return (crc & 0xffffffff) >>> 0;
};

Tested with values generated using http://www.sunshine2k.de/coding/javascript/crc/crc_js.html