code: func (r *RuntimeSort) OriginalPosition(ix int) int {
  	if ix < 0 || ix > len(r.origPosition) {
  		return -1
  	}
  	return r.origPosition[ix]
  }
docs: // OriginalPosition returns the starting (original) position of a particular index.
  // e.g. If OriginalPosition(0) returns 5 than the
  // the item currently at position 0 was at position 5 in the original unsorted array.