/**
 * Copyright 2013 Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @providesModule adler32
 */

/* jslint bitwise:true */

"use strict";

var MOD = 65521;

// This is a clean-room implementation of adler32 designed for detecting
// if markup is not what we expect it to be. It does not need to be
// cryptographically strong, only reasonable good at detecting if markup
// generated on the server is different than that on the client.
function adler32(data) {
  var a = 1;
  var b = 0;
  for (var i = 0; i < data.length; i++) {
    a = (a + data.charCodeAt(i)) % MOD;
    b = (b + a) % MOD;
  }
  return a | (b << 16);
}

module.exports = adler32;
