"checksum" -Can nsrt fix that with clean roms?

z4ever · Post by **z4ever** » Sun Dec 14, 2008 2:03 pm

Just wonder what is contained in nsrt db.
I suppose checksum is some bytes contained in rom itself.Is that right?
Is that all clean sets in nsrt's db have good checksum?
If true what can we do if we get clean roms with no header but with bad/corrupt checksum?
What caused that?overdump or something else?Can nsrt fix them?

PS:maybe it easy to understand my question by thinking about this question below.
Is there any possiblity that a game dumped without any problem,but the rom contains a bad checksum?

Post by **Agozer** » Sun Dec 14, 2008 4:12 pm

What exactly do you mean by "clean roms"? if you mean unaltered roms, then 9 times out of then a rom with bad checksum means that it has been tampered with, be it because of poor dumping, hacks, hardpatched translations or some other modification.

NSRT contains info on all known good dumps as well as games with specific hacks/overdumps etc. that can be fixed with NSRT. A checksum in a SNES rom is a 32-bit integer. NSRT calculates this value and then compares it to the one it has in its database.

Post by **grinvader** » Sun Dec 14, 2008 5:03 pm

Agozer wrote:A checksum in a SNES rom is a 32-bit integer. NSRT calculates this value and then compares it to the one it has in its database.

Incorrect.

The 'checksum incorrect' thing is the internal SNES checksum. Two 16 bit values (checksum and inverse checksum).

NSRT checks against its database for a varied amount of hashes, including crc32, md5, whirlpool, sha512 and some more.

z4ever wrote:Just wonder what is contained in nsrt db.
I suppose checksum is some bytes contained in rom itself.Is that right?

Yes.

Is that all clean sets in nsrt's db have good checksum?

No.

If true what can we do if we get clean roms with no header but with bad/corrupt checksum?
What caused that?overdump or something else?Can nsrt fix them?

Depends what caused it. Some betas are known to have a bad checksum, you could manually fix them but then they wouldn't be technically 'clean' anymore.

Is there any possiblity that a game dumped without any problem,but the rom contains a bad checksum?

Yes there is.
As I already mentionned some prototypes and beta didn't have their internal checksum valid. Nothing serious, since the SNES doesn't do anything with that.

z4ever · Post by **z4ever** » Sun Dec 14, 2008 5:10 pm

What I mean clean rom is roms that in no-intro and can be sorted in InDB by nsrt.
I assume that some roms have no "good checksums" dumps/sets as I found nsrt's rom editing only contains overdump trimming&hacking fix.
With a rom in no-intro with noheader,I think I cannot do a trimming.
Also it in no-intro I think it's not a hacking rom.
So I think nsrt can not fix it to own a "good checksums".
So I think maybe nsrt contains some roms' info in nsrt's db but info about that rom contains no "good checksums" set.

PS:Thanks grinvader for your explanation.