[leereeves]

Prior art matters for patents, not copyrights. Carmack's code is still protected by copyright even if he didn't invent the algorithm.

And copyright doesn't prevent someone else from implementing the same algorithm, only from copying the code. If Microsoft had been able to copyright the fast inverse square root function, Carmack could still have written his own version and even copyrighted that version himself.

[williamcotton]

Prior art has been used for copyright in plenty of court cases, and increasingly so!

Here’s an example: https://scholar.google.com/scholar_case?case=728470765881077...

It seems particularly apt to consider prior art for use in software IP if only for the similarities with the patentable invention of mechanical parts.

[imtringued]

What? You are free to reverse engineer any non patented object and reproduce an almost identical object. Prior art for copyright is meaningless unless it is about authorship. You can still do a clean room implementation and ignore prior art.

[williamcotton]

But the current interpretation is that you cannot claim authorship over things that were already in the public domain. Feel free to read the case notes and follow some of the links in there for more info. Am I not interpreting the court rulings correctly?

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Considering de novo the evidence before the district court, we hold that the district court did not err in granting summary judgment. Johannsongs failed to offer admissible evidence to rebut Ferrara's analysis, so there is no genuine dispute of material fact as to his conclusions that Söknuður and You Raise Me Up are not substantially similar and most of their similarities are attributable to prior art. Based on these conclusions, Johannsongs has failed to satisfy the extrinsic test and Defendants are entitled to judgment as a matter of law.