When you say "short" and "long" do you mean short-term (shares you owned for a year or less) and long-term (shares you owned for more than a year)? Selling short, or a short sale, means something different. It means selling shares that you don't own, with the hope that the price will go down. (You borrow the shares, sell the borrowed shares, then buy later to cover the short sale.) I don't think you are really talking about selling short.
If you do mean that some of the shares were long-term and some were short-term, you cannot combine them. It does matter, even if you do not have a loss. Long-term gain is treated differently from short-term gain on your tax return. Long-term gain is taxed at lower rates than short-term gain.
