anchor.diff:    void operator []=(int index, bool value) {
       RangeError.checkValidIndex(index, this);
       if (value) {
  -      buffer[index >> SHIFT] |= SET_MASK[index & OFFSET];
  -    } else {
  -      buffer[index >> SHIFT] &= CLEAR_MASK[index & OFFSET];
  +      buffer[index >> bitShift] |= bitSetMask[index & bitOffset];
  +    } else {
  +      buffer[index >> bitShift] &= bitClearMask[index & bitOffset];
       }
     }
   
  
positive.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;
  
negative.code:   @override
    bool operator [](int index) {
      RangeError.checkValidIndex(index, this);
      return (buffer[index >> bitShift] & bitSetMask[index & bitOffset]) != 0;
    }
  
    /// Sets the [value] of the bit with the given [index].
  