Merge pull request #55 from sno2/perf/faster-btoa

perf(btoa): improve btoa() speed

base64.js

@@ -28,26 +28,32 @@
   InvalidCharacterError.prototype.name = 'InvalidCharacterError';
 
   // encoder
-  // [https://gist.github.com/999166] by [https://github.com/nignag]
   function btoa(input) {
-    var str = String (input);
-    for (
-      // initialize result and counter
-      var block, charCode, idx = 0, map = chars, output = '';
-      // if the next str index does not exist:
-      //   change the mapping table to "="
-      //   check if d has no fractional digits
-      str.charAt (idx | 0) || (map = '=', idx % 1);
-      // "8 - idx % 1 * 8" generates the sequence 2, 4, 6, 8
-      output += map.charAt (63 & block >> 8 - idx % 1 * 8)
-    ) {
-      charCode = str.charCodeAt (idx += 3 / 4);
-      if (charCode > 0xFF) {
+    var data = String (input), o1, o2, o3, bits, i = 0, acc = '';
+
+    while (i < data.length) {
+      // pack three octets into four hextets
+      o1 = data.charCodeAt (i++);
+      o2 = data.charCodeAt (i++);
+      o3 = data.charCodeAt (i++);
+
+      if (o1 > 128 || o2 > 128 || o3 > 128) {
         throw new InvalidCharacterError ("'btoa' failed: The string to be encoded contains characters outside of the Latin1 range.");
       }
-      block = block << 8 | charCode;
+
+      bits = (o1 << 16) | (o2 << 8) | o3;
+      // use hextets to index into b64, and append result to encoded string
+      acc += chars.charAt ((bits >> 18) & 0x3F) +
+             chars.charAt ((bits >> 12) & 0x3F) +
+             chars.charAt ((bits >>  6) & 0x3F) +
+             chars.charAt ((bits)       & 0x3F);
+    }
+
+    switch (data.length % 3) {
+      case 0: return acc;
+      case 1: return acc.slice (0, -2) + '==';
+      case 2: return acc.slice (0, -1) + '=';
     }
-    return output;
   }
 
   // decoder