adler32.js

/**
 * Copyright 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule adler32
 * @flow
 */

'use strict';

var MOD = 65521;

// adler32 is not cryptographically strong, and is only used to sanity check that
// markup generated on the server matches the markup generated on the client.
// This implementation (a modified version of the SheetJS version) has been optimized
// for our use case, at the expense of conforming to the adler32 specification
// for non-ascii inputs.
function adler32(data: string): number {
  var a = 1;
  var b = 0;
  var i = 0;
  var l = data.length;
  var m = l & ~0x3;
  while (i < m) {
    var n = Math.min(i + 4096, m);
    for (; i < n; i += 4) {
      b += (
        (a += data.charCodeAt(i)) +
        (a += data.charCodeAt(i + 1)) +
        (a += data.charCodeAt(i + 2)) +
        (a += data.charCodeAt(i + 3))
      );
    }
    a %= MOD;
    b %= MOD;
  }
  for (; i < l; i++) {
    b += (a += data.charCodeAt(i));
  }
  a %= MOD;
  b %= MOD;
  return a | (b << 16);
}

module.exports = adler32;