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Final Fantasy IV Research & Development / FF4 SNES SRM Checksum
« on: February 11, 2017, 10:23:22 PM »
Hello everybody,
I was pointed here by the nice folks at ff6hacking.com. Maybe somebody here can help me out.
I'm trying to figure out the algorithm for generating the save game checksum for Final Fantasy II on SNES (or 4 however you look at it). I know the file is 8kB long and is divided into 4 equally spaced 2kB blocks. The checksum from what I gather is at the end of this block. I've tried sums of the words, XORs of the words, and I'm really sort of lost as to how it's computed. I found a tool by Lord J - FF4H version 3B that implements this. That's great, but I'd like to know the calculation behind it. From looking at his freely available source code for FF3H, it does look like it's more or less a simple sum of the words in each slot, XORd with all 1's at the end. I don't think FF4 is quite the same. I also found a tool by Zyrthofar on this website that implements this algorithm, but there's no source available.
Side note: I'm a programmer, so I'd like to make my own tool for fun as opposed to using one of the currently available tools that are out there.
Thanks for any help you can provide.
I was pointed here by the nice folks at ff6hacking.com. Maybe somebody here can help me out.
I'm trying to figure out the algorithm for generating the save game checksum for Final Fantasy II on SNES (or 4 however you look at it). I know the file is 8kB long and is divided into 4 equally spaced 2kB blocks. The checksum from what I gather is at the end of this block. I've tried sums of the words, XORs of the words, and I'm really sort of lost as to how it's computed. I found a tool by Lord J - FF4H version 3B that implements this. That's great, but I'd like to know the calculation behind it. From looking at his freely available source code for FF3H, it does look like it's more or less a simple sum of the words in each slot, XORd with all 1's at the end. I don't think FF4 is quite the same. I also found a tool by Zyrthofar on this website that implements this algorithm, but there's no source available.
Side note: I'm a programmer, so I'd like to make my own tool for fun as opposed to using one of the currently available tools that are out there.
Thanks for any help you can provide.