3. Generation checksum calculation

Hi,

i've read so many threads about this now and i still dont understand it completely.

My plan was to create a Trading Programm for 3. gen, to trade Pokemon on the ti-nspire (a calculator) with friends.

The first problem was that my program swaps the first pokemon in the team in both savefiles, but both savefiles are ruined afterwards, because:

- the checksum of the whole section (1) was wrong, so i cant load the latest, but only the previous savefile in emulator)

- the checksum of each pokemon (only the swapped) was wrong -> bad egg (i looked it up in "A-Save", a 3. gen saveedit as i cant open the savefile in emulator)

edit: problem 2 solved now, i just shifted the whole pokemon section so things got messed up.

I've found some threads/websites about this topic:

- http://bulbapedia.bulbagarden.net/wiki/Save_data_structure_in_Generation_III#Checksum

- http://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9mon_data_structure_in_Generation_III

- http://furlocks-forest.net/wiki/?page=Pokemon_GBA_Save_Format (especially the comments of adam)

- http://projectpokemon.org/forums/showthread.php?1904-help-with-pokemon-checksum/

Can someone explain the checksum calculation in easy words with examples and maybe even pictures?

(expect me to be a 5 year old little child that knows how to google and use "goldfinger", "hexcmp2", "A-Save", "Vba Emulator" and some other pokemon/hexcode related tools)

Hopefully someone can help :smile:

edit: i also found the sourcecode of this program, but i dont understand what parameters i have to use for the Chksum() function:

https://dl.dropboxusercontent.com/u/12206225/PSavFixV2.zip

You can look at Chase's Pokémon save hacking library - I believe he has Gen III all figured out:

https://github.com/Chase-san/libspec

Specifically:

https://github.com/Chase-san/libspec/blob/master/include/game_gba.h and https://github.com/Chase-san/libspec/blob/master/src/game_gba.c

wow ...

Didnt expect anyone to make something like this...

I'll try to make use of it as soon as possible

thanks man

However, can i just take both the header and the c file, include them and use built-in functions to load, modify and save the .sav file?

On a technical level, I don't know a lot about the library, such as which dependencies those two files might have on other library files, but I think you're correct.

If you're asking for some kind of permission, well... it's open source for a reason, right? ;-)

sadly i dont know at all what i should do with the library as i cant make it run because every function is defined plenty of times but i see only one of them ...

/* Forget that shit please... was a typo in the first step that ruined everything...

However, how can i calculate the checksum... I get always wrong results...

Here's my savefile:

http://www.file-upload.net/download-9223985/Pokemon-Emerald-clean-save.sav.html

at offset 0x7ff4

i did it like this to calculate:

Sum of these:

FB2CFC2C (EDIT: its 2cfc2cfb anyway, second mistake here, but useless cuz typo)

509700D9

C7BFD1CE

D1C9FF00

00000202

CCBFBEFF

FFFFFF00

3BF50000

3DBBFCF5

37BBFCF5

AB44FCF5

ADBBFC09

57BBFCF5

ABBBFCF5

54BB79D4

544403CA

ABBBFC75

F6BB7DF5

DBBBFCF5

B2AFE2F5

= 9e9195ca5

now i cut off the highest bit to get 32 bits:

e9195ca5

adding the lower 16 and the higher 16 bits resulted in this:

e919 +

5ca5 =

145BE

truncated to 16 bits its 45 BE and sadly thats not DF 97 like in the savefile

Are these steps the right and i just made typo in the first step?

*/