Open source IPF implementation

[vadosnaprimer]

IPF used to be a format that only its creators supported via a library that used to be proprietary and then its source got released but it remained strictly non-commercial. Therefore it's not open source, and can't be directly included into an open source project.

For this reason, every Amiga emulator I could find supports IPF by letting users download CAPSimg separately, put it into the right place, and link it that way.

Turns out there are some open source implementations of an IPF loader, apparently based on reverse engineering the format itself (that's the case for MAME, haven't checked the others).

MAME's IPF importer amusingly was made 4 days before SPS released their code.

Another one I found is this:
https://github.com/Tom1975/CPCCore/blob/master/CPCCoreEmu/CAPSFile.cpp

MAME is perfectly capable of loading Turrican (Europe).ipf, it works fine (even though emulation is not perfect). In case Amiga needs to write to a disk, MAME offers some options that don't modify the original image.

If there are some less straightforward things about IPF that need to be tested, I'm happy to try them in MAME, just tell me what image to run (like canonical filename and hash), and what to pay attention to to see if everything actually works (I don't have a lot of experience with IPF myself).

PS: There's already a more generic issue for IPF, but midwan suggested I make a new one.

[RodimusFVC]

It would be nice if IPF files could be treated like the CHD format in mame, where any changes to the file are stored in a .dif file that is applied during usage - and if you want to drop back to the original file, you just delete the .dif. These are also stored in a 'diff' folder, so 'updates' can be kept out of the read-only tree. I'm not sure what all goes into the .dif file format, but I'd hope they track the hash/crc/sha of the original file so it doesn't try to apply diffs to the wrong image and end up with a corrupted mess in memory if someone replaces the underlying file with a newer/different one. These are my random thoughts. :)