I'm no fan of software patents but comparing a simple arithmetic operation to an algorithm is a bad way to argue about software patents. Algorithms are a higher level of abstraction that can be quite complex in the end. And they are rarely the unique way to do something. It can even be almost impossible that an algorithm is really the best choice in your case.

Do I think software patents (or any patents) make sense? No, but I won't call software algorithms simple mathematical expressions similar to adding 1+1.