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[E-reader] LZ77/Huffman .vpk compression with CaitSith2's nevpk tool


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Hi there people!

I was doing some research on how exactly e-reader cards work. I could figure out a bunch myself but now i'm stuck on the way the .vpk files inside a e-card are compressed.
When I decompress a .vpk file with CaitSith2's nevpk tool, everything goes well, but when I compress it back the "recompressed" .vpk looks totally different from the original compressed .vpk (when looking at hexadecimals). When decompressing with the tool, no option can be chosen, but when compressing, you can pick options like LZwindow, LZsize, Method 0 or 1 and Level 0, 1, 2 or 3.

Can someone explain to me if it is actually possible to decompress a .vpk file and then compress it back so that the newly compressed file is exactly the same as the original compressed file?
I want to know this, because then we know what exact compression Nintendo used for their e-reader cards, which is really interesting to me.

Thank you very much for reading and possibly responding!

Sunicune

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