crc32.js

'use strict';

// Note: we can't get significant speed boost here.
// So write code to minimize size - no pregenerated tables
// and array tools dependencies.


// Use ordinary array, since untyped makes no boost here
function makeTable() {
  var c, 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;
}

// Create table on load. Just 255 signed longs. Not a problem.
var crcTable = makeTable();


function crc32(crc, buf, len, pos) {
  var t = crcTable
    , end = pos + len;

  crc = crc ^ (-1);

  for (var i = pos; i < end; i++ ) {
    crc = (crc >>> 8) ^ t[(crc ^ buf[i]) & 0xFF];
  }

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


module.exports = crc32;