GPL: you know how it's done, but you have'nt seen the code, is then your own code GPL? [closed]

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Please imagine such a sutuation:

1. You found a piese of GPL'ed software. The software does thing "A".
2. Without looking at the source code of "A", you implement the same functionality of "A" yourself and put it into "MyA.cpp".
3. In such a case, do you have to license "MyA.cpp" as GPL?

Thanks in advance for your answer.

Answer 1

I am not a lawyer and this is not legal advice.

The GPL applies to software, i.e. copyrighted materials, not to ideas which are covered in IP law by patents. If you've never seen the source code for the original software and make a completely novel, "clean room" implementation, then you have copyright on that implementation and can usually(*) license it as you please. However, if you have seen the original program's source code, things get complicated. Of course, proving that you haven't seen the code when it's public is hard enough in itself.

This is in fact how the GNU project itself started off: they hired programmers to rewrite the Unix operating system, piece by piece, looking only at publicly available descriptions of how the system should work (manuals, books) but not its actual source code.

(*) There may be exceptions such as patented algorithms. I know too little about patent law to say anything sensible about it.