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S2 Nick Arcade's unknown compression is used in Kid Chameleon STI standard compression?

#1 User is offline Clownacy 

Posted 18 October 2016 - 11:26 AM

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Having got my feet wet with LZSS, I read up on Kosinski, Saxman, and Comper's compression schemes, all of which were supported in my Captain PlaneEd tool. I then remembered my tool supported an addition compression, which it inherited from the original PlaneEd project: "Kid Chameleon". The format was cracked some time ago, and (de)compressors were made for it.

Out of curiosity, I hunted down the original ASM decompressor in a Kid Chameleon disassembly. To my amazement, the decompressor looked identical to the ASM decompressor I'd seen in a Nick Arcade disassembly mere days ago. I used one of the Chameleon decompressors to decompress S2NA GHZ's chunks, and it worked.

Kid Chameleon also used Enigma, and was developed by STI. This leads me to the question of if this compression was a fourth 'standard' compression offered by Sega themself, along with Nemesis, Engima, and Kosinski. Though, as MainMemory pointed out to me, this could also be STI's own in-house compression.

You can find the decompressor labelled sub_13684 in the Kid Chameleon disassembly. A copy of it is below. It can be found in the Nick Arcade disassembly under the name UnknownDec.


This post has been edited by Clownacy: 18 October 2016 - 11:35 AM

#2 User is offline Caverns 4 

Posted 19 October 2016 - 02:11 PM

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That's good to know - I wondered about the "Unknown" compression in Sonic 2 NA, and why it was in the ROM for all of like, 2 things, and that does shed a small amount of light on at least what it is... Heaven knows why they felt the need to use a different compression for GHZ's blocks/Chunks in the first place, though.

Good eye, spotting that though, I had no idea what that format was.

#3 User is offline Billy 

Posted 19 October 2016 - 08:33 PM

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Given that GHZ was leftover from a previous point in development, it's possible that they intended to use this compression algorithm but then changed their minds. Or maybe they were just experimenting with it.

#4 User is offline kazblox 

Posted 19 October 2016 - 08:49 PM

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It's probably the latter. Maybe it could have been one of Sega Technical Institute's first coding exercises while collaborating with Sonic Team.

As an interesting footnote, Kid Chameleon was released in America on May 28, 1992. That was around the time that the Sonic 2 Nick Arcade build was presumably assembled.

#5 User is offline Cooljerk 

Posted 23 October 2016 - 04:32 AM

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So are we gonna start calling this Clownacy compression? :v:

And will this be worked into KENS?

#6 User is offline Clownacy 

Posted 23 October 2016 - 01:46 PM

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I'm still trying to figure the format out, but if I do, I'll see if I can make it part of FW-KENSC, like I did with Rocket.

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