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:   /// value.
    void flip(int index) {
      RangeError.checkValidIndex(index, this);
      flipUnchecked(index);
    }
  
    /// Sets the bit at the specified [index] to the complement of its current
    /// value. The behavior is undefined if [index] is outside of bounds.
    @pragma('vm:prefer-inline')
    @pragma('dart2js:tryInline')
    void flipUnchecked(int index) =>
        buffer[index >> bitShift] ^= bitSetMask[index & bitOffset];
  
    /// Counts the number of bits that are set to [expected].
    int count([bool expected = true]) {
  