As promised below I’ve put a bit of time into hooking up 7-zip support in MAME. This is a first pass, so there is still room for improvements (both to code quality, and potentially bug fixes)
The way I see it zip / 7z offer the following pros / cons
– Aging 32-bit format
– Can only hold 2gb of data (we’re hitting that limit in some cases)
– Only supports UTF-8 filenames
– Single, dated algorithm
+ low memory overhead
+ Modern 64-bit format
+ No practical limitation to filesizes
+ UTF16 support (debatable advantage)
+ newer more advanced algorithms
– higher memory overhead if ‘solid’ blocks are used
Zlib (.zip support) might be tried and tested, but it’s showing it’s age, it’s a format of the previous decade when FAT32 was the standard, and nobody had large files. .7z is newer and doesn’t have many of the inherent issues of an older format, although does still need some testing. Staying ahead of the game is always a good idea tho, better to be modern and be prepared.
Download the diff here. This has been sent to R.Belmont for portability checking and official inclusion. Right now this can be used for roms, artwork, samples, cheats etc. -romident and romcmp.exe aren’t hooked up to it yet, but that will come with time. As I said, this is first pass, and a demonstration it works.
I’ve tested this with a wide range of settings in the Windows 7-zip binary and haven’t managed to make a file which fails to decompress yet. Both 32-bit and 64-bit Windows MAME builds have been tested and as long as you’re sensible about block sizes and compression used speed / memory overhead is comparable to standard .zip (ie don’t use PPmd with huge block sizes on huge ROMs because that would just be stupid and can take a good 3 minutes to decompress kof2003.zip even with the official tools ;-)
I’m increasingly being sent .7z files when asked to look at things to work on in MAME as opposed to zips in days gone by. I’d attribute a lot of this to the decline of WinZip (they practically nuked their own business model) as well as the horrendous build-in Zip support Windows has, forcing people to look for alternatives. This means having .7z support makes MAME work easier as I don’t have to decompress / recompress everything just to check it out. Weigh that up with the limitations of the format and moving forward seems like a good idea. I’m also often sent .rar files (because people appear to have flocked to either 7-zip or WinRAR in equal numbers) but I need to do further investigation on the suitability of decompression code for those, there are a few strings attached because it’s not a ‘free’ format.
Of course, the original .zip support remains, .7z is just an option. There is no reason to rip out the long standing .zip support, merely supplement it with something more modern.
The other benefit of course is that the LMZA and LMZA2 algorithms will be in the MAME code for leverage elsewhere, and would be ideal for use in CHDs and such. Not done anything on that front tho because it’s not a priority, and the FLAC work is still pending cleanups and being officially turned on.