crc32.js

/**
 * Calculates the CRC32 checksum of a Buffer
 */

/* Table of CRCs of all 8-bit messages. */
var crc_table = new Array(256);

/* Make the table for a fast CRC. */
(function() {
  var c;
  var n, k;

  for (n = 0; n < 256; n++) {
	  c = n;
	  for (k = 0; k < 8; k++) {
		  if (c & 1)
			  c = -306674912 ^ (c >>> 1);
		  else
			  c = c >>> 1;
	  }
	  crc_table[n] = c;
      //console.log(n + ' ' + c);
  }
}());


/* Update a running CRC with the bytes buf[0..len-1]--the CRC
should be initialized to all 1's, and the transmitted value
is the 1's complement of the final running CRC (see the
crc() routine below)). */

function update_crc(crc, buf, len)
{
	var c = crc;
	var n;

	for (n = 0; n < len; n++) {
		c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >>> 8);
	}
	return c;
}

/* Return the CRC of the bytes buf[0..len-1]. */
exports.crc32 = function crc32(buf)
{
	return (update_crc(0xffffffff, buf, buf.length) ^ 0xffffffff);
};