You can't copyright the functionality of a software program. Copyright is a fixed expression. You can't copyright a song about heartbreak and you can't copyright the idea of a four function calculator implemented in a GUI.
You may be able to patent the functionality of a piece of software.
The point of the clean room practice is to avoid a literal line for line copy of the original software. It would be entirely legal to say, write a song from the perspective of Taylor Swift about her feeling sad and betrayed after a breakup.
But analogies are dicey because the law treats functional software differently from literary expression.
Precedent here is vTech reimplementing the Apple II BIOS and Phoenix reimplementing the IBM BIOS and Connectix selling a PlayStation emulator for a fraction of the price of a PlayStation.
You may be able to patent the functionality of a piece of software.
The point of the clean room practice is to avoid a literal line for line copy of the original software. It would be entirely legal to say, write a song from the perspective of Taylor Swift about her feeling sad and betrayed after a breakup.
But analogies are dicey because the law treats functional software differently from literary expression.
Precedent here is vTech reimplementing the Apple II BIOS and Phoenix reimplementing the IBM BIOS and Connectix selling a PlayStation emulator for a fraction of the price of a PlayStation.