anchor.diff:  
     /// Returns the value of the bit with the given [index]. The behavior is
     /// undefined if [index] is outside of bounds.
  +  @pragma('vm:prefer-inline')
  +  @pragma('dart2js:tryInline')
     bool getUnchecked(int index) =>
         (buffer[index >> bitShift] & bitSetMask[index & bitOffset]) != 0;
   
  
positive.code:     setUnchecked(index, value);
    }
  
    /// Sets the [value] of the bit with the given [index].  The behavior is
    /// undefined if [index] is outside of bounds.
    void setUnchecked(int index, bool value) {
      if (value) {
        buffer[index >> bitShift] |= bitSetMask[index & bitOffset];
      } else {
        buffer[index >> bitShift] &= bitClearMask[index & bitOffset];
      }
    }
  
    @override
    BitList operator +(List<bool> other) {
  
negative.code: // Constants specific to mapping bits into a [UInt32List].
  const int bitShift = 5;
  const int bitOffset = 31;
  const int bitCount = bitOffset + 1;
  const int bitMask = 0xffffffff;
  const List<int> bitSetMask = [
    1,
  