anchor.diff:    @override
     bool operator [](int index) {
       if (0 <= index && index < length) {
  -      return (buffer[index >> _shift] & _setMask[index & _offset]) != 0;
  +      return (buffer[index >> SHIFT] & SET_MASK[index & OFFSET]) != 0;
       } else {
         throw new RangeError.range(index, 0, length);
       }
  
positive.code:   int count([bool expected = true]) {
      var tally = 0;
      for (var index = 0; index < length; index++) {
        var actual = (buffer[index >> _shift] & _setMask[index & _offset]) != 0;
        if (actual == expected) {
          tally++;
        }
  
negative.code:   /// Constructs a new list from a given [Iterable] of booleans.
    factory BitList.from(Iterable<bool> other) {
      var length = other.length;
      var buffer = new Uint32List((length + OFFSET) >> SHIFT);
      if (other is BitList) {
        buffer.setAll(0, other.buffer);
      } else {
        for (var i = 0, iterator = other.iterator; i < buffer.length; i++) {
          var value = 0;
          for (var j = 0; j <= OFFSET && iterator.moveNext(); j++) {
            if (iterator.current) {
              value |= SET_MASK[j];
            }
          }
          buffer[i] = value;
  