SNES Checksum calculation.

[KingMike]

So, out of curiousity, I dumped my Slapstick cart with a tototek dumper. It dumped a 2MB ROM. I noticed it had a different CRC (FDF11B50) than the existing GoodSNES CRC (53FB163B).
So I read Slapstick/Robotrek's proper size is 1.5MB.
I cut off the last 512KB, then it results in the same CRC as the existing dump.
So, 16mbit is just a sum of all bytes in the ROM.
12 mbit is a sum of (first 8mbit) + ( (last 4mbit) x 2 ).
If the last 4mbit (0x180000-0x1FFFFF) of a 16mbit ROM is physically identical to the preceeding 4mbit (0x100000-0x17FFFF), shouldn't that 16mbit sum produce the same CRC as the 12mbit?

[Deathlike2]

Think about it. The answer is no. Even if that data is padded, it's factored into the CRC check. That's why it fails.

[grinvader]

Calculate it manually with a 16-byte example similar to your data, i.e.

AaaaaaaaBbbbBbbb

8 + 4 (mirrored to 16).

and compare with

AaaaaaaaBbbb