1  /* -*- Mode: js; js-indent-level: 2; -*- */
 2  /*
 3   * Copyright 2011 Mozilla Foundation and contributors
 4   * Licensed under the New BSD license. See LICENSE or:
 5   * http://opensource.org/licenses/BSD-3-Clause
 6   */
 7  
 8  var intToCharMap = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'.split('');
 9  
10  /**
11   * Encode an integer in the range of 0 to 63 to a single base 64 digit.
12   */
13  exports.encode = function (number) {
14    if (0 <= number && number < intToCharMap.length) {
15      return intToCharMap[number];
16    }
17    throw new TypeError("Must be between 0 and 63: " + number);
18  };
19  
20  /**
21   * Decode a single base 64 character code digit to an integer. Returns -1 on
22   * failure.
23   */
24  exports.decode = function (charCode) {
25    var bigA = 65;     // 'A'
26    var bigZ = 90;     // 'Z'
27  
28    var littleA = 97;  // 'a'
29    var littleZ = 122; // 'z'
30  
31    var zero = 48;     // '0'
32    var nine = 57;     // '9'
33  
34    var plus = 43;     // '+'
35    var slash = 47;    // '/'
36  
37    var littleOffset = 26;
38    var numberOffset = 52;
39  
40    // 0 - 25: ABCDEFGHIJKLMNOPQRSTUVWXYZ
41    if (bigA <= charCode && charCode <= bigZ) {
42      return (charCode - bigA);
43    }
44  
45    // 26 - 51: abcdefghijklmnopqrstuvwxyz
46    if (littleA <= charCode && charCode <= littleZ) {
47      return (charCode - littleA + littleOffset);
48    }
49  
50    // 52 - 61: 0123456789
51    if (zero <= charCode && charCode <= nine) {
52      return (charCode - zero + numberOffset);
53    }
54  
55    // 62: +
56    if (charCode == plus) {
57      return 62;
58    }
59  
60    // 63: /
61    if (charCode == slash) {
62      return 63;
63    }
64  
65    // Invalid base64 digit.
66    return -1;
67  };