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Old 10-21-2005, 02:22 AM   #1
JadussD
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Join Date: Jan 2003
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Default SNES ROM Checksums.

I was reading the http://www.emulatronia.com/doctec/co...bededcartridgeSNESKart</A> document, which is excellent, except for some ambiguity on the subject of the checksum. It says that SNES ROM checksums are 16-bit, but they are obtained by adding together all the bytes in 4Mbit chunks, then adding these chunks together and taking the lower 32-bits. Obviously, the checksum cannot be 32-bits, if there is only 16-bits to store it in. What gives?

It also says some confusing things about what to do whenever the ROM size is not evenly divided by 4Mbit. So, if I have a 10Mbit ROM (Were any commercial games actually of this size or is worrying about this a waste of time?), would I have to multiply the result of the last 2Mbit by itself, or simply add 0s where the non-existant space is? The document is ambiguous on the matter. Also, could anyone tell me any games that were of a size indivisible by 4Mbit (524,288 bytes) if any?
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Old 02-02-2011, 06:54 PM   #2
Videogamer555
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Default

So do you apply Data AND $FFFF after each addition? Or do you do all additions and then perform AND $FFFF the final sum? Please explain what's going on here.
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