dart base64 perf test.

gistfile1.dart

import 'dart:math';

var random = new Random(0xCAFEBABE);

/// The base64 encoding table
final List<int>characters = const [
  // A-Z [65-90]
  65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90,
  // a-z [97-122]
  97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122,
  // 0-9 [48-57]
  48, 49, 50, 51, 52, 53, 54, 55, 56, 57,
  // + / =
  43, 47, 61
];

_btoa(List<int> bytes, List<int> out, int j, int len) {
  int a, b, c, b1, b2, b3, b4, i=0;
  while (i < len) {
    a = bytes[i++];
    b = bytes[i++];
    c = bytes[i++];

    b1 = (a >> 2) & 0x3F;
    b2 = ((a & 0x3) << 4) | ((b >> 4) & 0xF);
    b3 = ((b & 0xF) << 2) | ((c >> 6) & 0x3);
    b4 = c & 0x3F;
    if (len==3)
       b!=0 ? c!=0 ? 0 : b4 = 64 : b3 = b4 = 64;

    out[j++]=characters[b1];
    out[j++]=characters[b2];
    out[j++]=characters[b3];
    out[j++]=characters[b4];
  }
}

String btoa(List<int> bytes) {
    var tailLen=bytes.length % 3,
        bodyLen = bytes.length-tailLen,
        array=new List<int>((bodyLen~/3)*4+(tailLen==0?0:4));

    _btoa(bytes, array, 0, bodyLen);
    if (tailLen !=0) {
      _btoa(<int>[bytes[bodyLen], tailLen==2?bytes[bodyLen+1]:0, 0],
          array, (bodyLen~/3)*4, 3);
    }
    return new String.fromCharCodes(array);
}

fillRandom(List<int> l) {
  for(int j=0; j < l.length; j+=2) {
    l[j] = random.nextInt(255);
    l[j+1]=0;
  }
}

String encodeTest(List<int> l, int iterations) {
  String enc;
  for( int i = 0; i < iterations; ++i ) {
    enc = btoa(l);
  }
  return enc;
}

void main() {
  var l = new List<int>(1024);
  var iterations = 20000;
  fillRandom(l);
  // Warm-up
  String enc;
  enc = encodeTest(l, 1000);
  var w = new Stopwatch()..start();
  enc = encodeTest(l, iterations);
  print("Encode for $iterations is ${w.elapsedMilliseconds} msec");
}