tongshanred/node_modules/pngjs/lib/crc.js

'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;
};