Maybe the best way is to write it yourself and when you face an issue you try to see how they solved it? It's fairly doable to understand a small part of the co

Maybe the best way is to write it yourself and when you face an issue you try to see how they solved it? It's fairly doable to understand a small part of the code until you see what they needed to do. I wouldn't call it reading all the millions of lines,I agree with OP that that would most likely take longer.