crc32中的简单例子

	function crcTable(arr, append) {
		var crc, i, l;

		// if we're in append mode, don't reset crc
		// if arr is null or undefined, reset table and return
		if (typeof crcTable.crc === 'undefined' || !append || !arr) {
			crcTable.crc = 0 ^ -1;

			if (!arr) {
				return;
			}
		}

		// store in temp variable for minor speed gain
		crc = crcTable.crc;

		for (i = 0, l = arr.length; i < l; i += 1) {
			crc = (crc >>> 8) ^ table[(crc ^ arr[i]) & 0xff];
		}

		crcTable.crc = crc;

		return crc ^ -1;
	}