pngjs/lib/crc.js

// Copyright (c) 2012 Kuba Niegowski
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

'use strict';

var crcTable = [];

(function() {
  for (var i = 0; i < 256; i++) {
    var currentCrc = i;
    for (var j = 0; j < 8; j++) {
      if (currentCrc & 1) {
        currentCrc = 0xedb88320 ^ (currentCrc >>> 1);
      } else {
        currentCrc = currentCrc >>> 1;
      }
    }
    crcTable[i] = currentCrc;
  }
}());

var CrcCalculator = module.exports = function() {
  this._crc = -1;
};

CrcCalculator.prototype.write = function(data) {

  for (var i = 0; i < data.length; i++) {
    this._crc = crcTable[(this._crc ^ data[i]) & 0xff] ^ (this._crc >>> 8);
  }
  return true;
};

CrcCalculator.prototype.crc32 = function() {
  return this._crc ^ -1;
};


CrcCalculator.crc32 = function(buf) {

  var crc = -1;
  for (var i = 0; i < buf.length; i++) {
    crc = crcTable[(crc ^ buf[i]) & 0xff] ^ (crc >>> 8);
  }
  return crc ^ -1;
};