use hardcoded ranges instead of indexOf

lib/b64.js

@@ -1,10 +1,30 @@
-(function (exports) {
-  'use strict';
+var lookup = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
+
 
-  var lookup = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
+;(function (exports) {
+  'use strict';
 
-  function decode (c) {
-    return indexOf(lookup, c)
+  var ZERO   = '0'.charCodeAt(0)
+  var PLUS   = '+'.charCodeAt(0)
+  var SLASH  = '/'.charCodeAt(0)
+  var NUMBER = '0'.charCodeAt(0)
+  var LOWER  = 'a'.charCodeAt(0)
+  var UPPER  = 'A'.charCodeAt(0)
+
+  function decode (elt) {
+    var code = elt.charCodeAt(0)
+    if(code === PLUS)
+      return 62 // '+'
+    if(code === SLASH)
+      return 63 // '/'
+    if(code < NUMBER)
+      return -1 //no match
+    if(code < NUMBER + 10)
+      return code - NUMBER + 26 + 26
+    if(code < UPPER + 26)
+      return code - UPPER
+    if(code < LOWER + 26)
+      return code - LOWER + 26
   }
 
   function b64ToByteArray(b64) {
@@ -91,9 +111,14 @@
 
   module.exports.toByteArray = b64ToByteArray;
   module.exports.fromByteArray = uint8ToBase64;
+  module.exports.indexOf = indexOf
+  module.exports.lookup = lookup
 }());
 
+
+
 function indexOf (arr, elt /*, from*/) {
+
   var len = arr.length;
 
   var from = Number(arguments[1]) || 0;
@@ -111,3 +136,4 @@ function indexOf (arr, elt /*, from*/) {
   }
   return -1;
 }
+