code: protected void append(RoaringArray sa, int startingIndex, int end) {
      extendArray(end - startingIndex);
      for (int i = startingIndex; i < end; ++i) {
        this.keys[this.size] = sa.keys[i];
        this.values[this.size] = sa.values[i];
        this.size++;
      }
    }
docs: Append the values from another array, no copy is made (use with care)
  
  @param sa other array
  @param startingIndex starting index in the other array
  @param end endingIndex (exclusive) in the other array