Snes9x.com

OV2 wrote: ↑Mon Nov 23, 2020 3:57 pm As long as the ROM has a size that is a multiple of 512KB, then this mirror algorithm is used (and it works the same below 1MB as above).
If it is not a multiple of 512KB, then it simply calculates the sum over the whole orignial ROM size, without any mirroring.

Got it, thanks again!

For non power of two sizes the idea is to take the largest power of two block, then look at the remaining size in power of two parts, and mirror until you have another block of the largest size. Then the end result is also a power of two. If you have multiple smaller parts you always mirror the sma...

There is no difference in the calculation for a 20MBit and a 27MBit ROM. What caused you problems in checksum_mirror_sum? Maybe you can describe how you think it is calculated for a 20Mbit ROM? From what I understand, for a 20MBit ROM, its (Sum of the first 16MBit) + 4*(Sum of the last 4MBit), rema...

Hi, I'd like to know how snes9x does the calculation of the "Actual checksum" for odd sized SNES roms. I have a rom hack thats 27MBits and want to know how it is performed. I know how the algorithm works for power-of-2-roms and evenly sized roms (e.g. 10/12/20MBit), but not for snes9x's im...