Chrono Cross PS1 Memory Card Checksum

[spamzilla]

I'm having an issue with trying to hack a PS1 memory card save checksum. The game is Chrono Cross and the format is .MCS from the pSX emulator. I have provided two files to illustrate the issue. The only difference between them is address 0x13E7 and the last four bytes which are probably the checksum. It isn't a Checksum-32 or any other common checksum that I know of. I ran it through a web-based checksum fixer but I would rather just write my own editor program than use that one.

Chrono Cross.7z

[Sparagas]

In Silent Hill 1 on PS1 checksum is just a simple XOR operation on all bytes. Maybe this is the same

[spamzilla]

I wrote some code to check this but it doesn't seem to work

for (int aa = 0; aa < byteFile.Length - 4; aa++)
{
	fileSum ^= byteFile[aa];
}

 

[Sparagas]

No, not the whole memory card. Try only on the save block, or more realistically only on one of the structures inside the save block. It is not for the whole memory card.

Edited 42 minutes ago by Sparagas

[spamzilla]

That code wasn't meant for the whole memory card but I can see how it could be construed that way.