crc32.js

function() {

      // persist the table so it doesn't need to be created every time
      var crcTable = null;

      var makeCrcTable = function() {
         var c;
         var table = [];
         for (var n = 0; n < 256; n++) {
            c = n;
            for (var k = 0; k < 8; k++) {
               c = ((c & 1) ? (0xEDB88320 ^ (c >>> 1)) : (c >>> 1));
            }
            table[n] = c;
         }
         return table;
      };

      this.calc = function(str) {

         // http://stackoverflow.com/a/18639999/571637

         var table = crcTable || (crcTable = makeCrcTable());
         var crc = 0 ^ (-1);

         for (var i = 0; i < str.length; i++) {
            crc = (crc >>> 8) ^ table[(crc ^ str.charCodeAt(i)) & 0xFF];
         }

         return (crc ^ (-1)) >>> 0;
      };
   }