Gyb checksum formula - Githubissues

Wohlstand / OPN2BankEditor

A small cross-platform editor of the OPN2 FM banks of different formats (Downloads in README below)

GNU General Public License v3.0

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Gyb checksum formula #61

Closed jpcima closed 4 years ago

jpcima commented 5 years ago

By chance I found the checksum formula of this file format which was previouly unknown. The project vgmpre has it, where it is known as "nineko's crazy checksum formula".

Judging from code, I guess we can say it's a somewhat fitting description. https://github.com/vgmtool/vgm2pre/blob/f4f917df35d531512292541234a5c1722b8af96f/vgm2pre/fmt/gyb.hpp#L30-L70

Wohlstand commented 5 years ago

So, let's try to implement this and check will midi2vgm accept the result?

jpcima commented 5 years ago

Oh it's a minor thing, I wanted to keep note because I've found it during research of formats. Are other software known to use this format?

Wohlstand commented 5 years ago

Are other software known to use this format?

Idk, mainly those midi2vgm and it's editor

jpcima commented 5 years ago

I found again an old post where ValleyBell talks of a newer revision of Gyb known as v3 (Nov 2018). It is suggested to have support of bank MSB+LSB through linked editor software. This software has source code with the Gyb loader. At first look, it has a case for FileVer based on 3 different versions. http://forums.sonicretro.org/index.php?s=9007c6bcd222e60acc7e3e2f044313ce&showtopic=25337&view=findpost&p=934762

ValleyBell commented 4 years ago

If you want a GYB checksum implementation, feel free to use the one from 2612_checksum.c that's included in the mid2smps 0.3.5 source code (subfolder OPNInsEdit)

So far the GYB format is only used by midi2vgm YM2612 and mid2smps. The latter is pretty popular in the Sonic hacking scene.

Wohlstand commented 4 years ago

So far the GYB format is only used by midi2vgm YM2612 and mid2smps. The latter is pretty popular in the Sonic hacking scene.

I see, BTW, some recent time I made my own MIDI2VGM with using of libOPNMIDI core:

The tool: https://github.com/Wohlstand/libOPNMIDI/blob/master/utils/midi2vgm/midi2vgm.cpp
The actual writer: https://github.com/Wohlstand/libOPNMIDI/blob/master/src/chips/vgm_file_dumper.cpp Processing of channels and music playing libOPNMIDI is doing. Yeah, libOPNMIDI initially is the MIDI synthesizer over OPN2 and OPNA chips, however, knowing some tricks I made the MIDI2VGM tool with basing on capturing of OPN commands and sending them into VGM file. Files are appearing non-optimized and their size would have more than 1 MB. However, your vgm_cmp squishes it into a few kilobytes size (except files are getting too many arpeggios due to voice channels overuse because of notes mess).

jpcima commented 4 years ago

This was implemented in the latest GYB format updates.