base64.js #1

/* -*- Mode: js; js-indent-level: 2; -*- */
/*
 * Copyright 2011 Mozilla Foundation and contributors
 * Licensed under the New BSD license. See LICENSE or:
 * http://opensource.org/licenses/BSD-3-Clause
 */
{
  var intToCharMap = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'.split('');

  /**
   * Encode an integer in the range of 0 to 63 to a single base 64 digit.
   */
  exports.encode = function (number) {
    if (0 <= number && number < intToCharMap.length) {
      return intToCharMap[number];
    }
    throw new TypeError("Must be between 0 and 63: " + number);
  };

  /**
   * Decode a single base 64 character code digit to an integer. Returns -1 on
   * failure.
   */
  exports.decode = function (charCode) {
    var bigA = 65;     // 'A'
    var bigZ = 90;     // 'Z'

    var littleA = 97;  // 'a'
    var littleZ = 122; // 'z'

    var zero = 48;     // '0'
    var nine = 57;     // '9'

    var plus = 43;     // '+'
    var slash = 47;    // '/'

    var littleOffset = 26;
    var numberOffset = 52;

    // 0 - 25: ABCDEFGHIJKLMNOPQRSTUVWXYZ
    if (bigA <= charCode && charCode <= bigZ) {
      return (charCode - bigA);
    }

    // 26 - 51: abcdefghijklmnopqrstuvwxyz
    if (littleA <= charCode && charCode <= littleZ) {
      return (charCode - littleA + littleOffset);
    }

    // 52 - 61: 0123456789
    if (zero <= charCode && charCode <= nine) {
      return (charCode - zero + numberOffset);
    }

    // 62: +
    if (charCode == plus) {
      return 62;
    }

    // 63: /
    if (charCode == slash) {
      return 63;
    }

    // Invalid base64 digit.
    return -1;
  };
}