Software Piracy???

Actually, unless I'm talking out of my hat, you'd have to make major changes in the code. To use another similarity: Two writers each write a novel about a true murder. Parts of it will be the similar, the murder, how it happened, and the general information. Maybe a few of the sentences will even be the same. But the books themselves will be so different that neither author would be able to claim copyright infringement.

The entire software code would have to be rewritten, in other words.

All of these are good points,but I think we're all forgetting the "clean room" approach to reverse engineering.For those that have never heard of it,it was made famous by Pheonix to functionally duplicate IBM BIOSes.To do this they hired two teams of engineers,the second team consisted of people who had never seen or studied an IBM BIOS(or at least were willing to testify to that in court).The first team studied the BIOS and wrote a complete description as possible of what the BIOS did.Then finally,the second team read the description and made a BIOS from scratch that did the exact same thing as the IBM BIOS.The technique survived all legal attacks,because you can't intentionally duplicate something you have absolutely no knowledge of.Although none of this was a direct quote,I got the info from Upgrading and Repairing PC's 10th edition.How I remembered that was in there is beyond me,as it's been at least 2 years since I've read it.