[PS2] Need help figuring out what to do next!

[rufaswan]

I can see why this game trip you up. I don't think I saw this kind of compression algorithm before. But I have a good understanding of it now.

Let's use an example for a start, you want to duplicate 0xC9 for 0x40 times. First you use method 6 for 0x1f+2 bytes, so you'll get "DF C9". For the remaining 0x1f bytes, you repeat the last command, or method 0, but with length 0x1d+2 instead, so you'll get "1D".

Hence, the compressed data to duplicate 0xC9 for 0x40 times is "DF C9 1D".

And the game keep the last 6 commands as history, or method 0 to 5.

The whole decompression goes:

read one byte for METHOD and LEN

Code:

METHOD = BYTE >> 5
LEN = BYTE & 0x1f

if the METHOD is 6, read next byte as BYTE, and then duplicate it for LEN + 2 times to output.

if the METHOD is 7, read the next LEN + 1 bytes as STRING and output it.

For both, add it to HISTORY[0] and push the queue down.

Code:

HISTORY[5] = HISTORY[4]
HISTORY[4] = HISTORY[3]
HISTORY[3] = HISTORY[2]
HISTORY[2] = HISTORY[1]
HISTORY[1] = HISTORY[0]
HISTORY[0] = current

For METHOD 0 to 5, set that as current, and re-queue everything before it. For example, METHOD 3 would

Code:

HISTORY[5] // do nothing
HISTORY[4] // do nothing
current = HISTORY[3]
HISTORY[3] = HISTORY[2] // re-queue
HISTORY[2] = HISTORY[1] // re-queue
HISTORY[1] = HISTORY[0] // re-queue
HISTORY[0] = current // re-queue

If the repeat METHOD is 6, duplicate the same BYTE but with new LEN + 2 times.

If the repeat METHOD is 7, then get SUB_POS and SUB_LEN from LEN

Code:

SUB_POS = LEN >> 2
SUB_LEN = LEN & 3

referring to the same STRING, output SUB_LEN + 1 bytes, starting from position SUB_POS.

That's about it.

The code has already uploaded to my github. You can run them by follow the Setup section of tutorial on my signature.

Then run

Code:

php  psxtools/ps2_zero_hd-bin.php  SCENEDAT.hd

I also noticed there are 3 Zero no Tsukaima games from the same company on PS2, and they are all using the same SCENEDAT hd+bin set. So I updated the script to support all 3 of them.

Sample




Have fun!
- Rufas