The company I am currently working on is patenting a software feature that I have used in my private project. My private project is very old and has been using this technique/feature for a long time. The company in question came across this recently and decided to patent it. What are my options to avoid having to rewrite the whole feature in a new way (i.e. invent a new idea to keep my software working)? If there are no options, is making the software public going to work?
How did the company "come across" the feature? Was it by reviewing your "private project?" If so, then maybe your project wasn't really that private and itself constitutes prior art.
But, yes, making the software public (and preserving any documentation you have that demonstrates the age of your solution) should go a long way towards ultimately preventing someone else from patenting it. You may want to notify both the company and the patent office of this, once you publish it and document the fact that you did it a while ago. Then you have the option of starting what's called an "interference," which could result in you getting any patent, or in preventing the company from getting the patent. If you're happy preventing any patent from issuing, then maybe you can do some internet research on your own and take a stab at it. You'd probably still benefit from the assistance of an attorney. If you'd like to go the interference route, then you should certainly consider an attorney.
However, I'm worried about the fact that you work "on" this company. You may want to make sure that this scenario isn't affected by your relationship with the company.
Pre-AIA 35 U.S.C. 102 Conditions for patentability; novelty and loss of right to patent. I think you can use this....if not simply declaring it your own personal trade secret (since you didn't invent it while working for the company). I'd just object to their attempt to patent it and point out that you did use it in your own work, in years prior.
The patent rules read.
A person shall be entitled to a patent unless -
(b) the invention was patented or described in a printed publication in this or a foreign country or in public use or on sale in this country, more than one year prior to the date of application for patent in the United States.