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First post, by Stiletto

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From here:
showthread.php?s=&threadid=214

WinRAR was used to package these files at a 39% greater compression ratio than could be achieved using standard ZIP archiving. (1.31MB for ZIP vs. only 372KB for RAR)

Well, go do some reading:
http://www.cmetge.dixinet.com/compression.asp
http://www.cmetge.dixinet.com/archive.asp
http://www.compression.ca/

WinRAR is by no means the "best". But it is surely one of the best popular ones.

Currently, 7-zip (http://www.7-zip.com) has obtained a level of popularity in the emulation world as a file rezipper. See also here:
ZipMax - http://www.clrmame.com/download.htm
AdvanceScan - http://advancemame.sourceforge.net/scan-readme.html

Some comments from the author of AdvanceScan:

Some months ago I did a lot of testing on the 7zip compression algorithm (called LZMA). […]
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Some months ago I did a lot of testing on the 7zip compression algorithm (called LZMA).

The first thing discovered is that this algo is for sure better than all the others RAR, ACE, bzip2 (BWT), PPM, ... when recompressing roms.

The second thing is that you can't save a lot of space. Recompressing the whole romset you can save approximately only 550 MB respect the standard deflate implementation with maximum compression (pkzip, winzip, zlib).
And only 450 MB respect the 7zip deflate implementation.

These are the size of a complete romset with different compression :

zlib-deflate 4,606,494,475 bytes
7zip-deflate 4,503,914,469 bytes
7zip-lzma 4,026,339,475 bytes
See this thread:
http://sourceforge.net/mailarchive/forum.php? … 44&forum_id=718

And a few more comments from another MAMEDEV member regarding the security of MD5 and CRC32:

We use the checksum system to identify the ROMs, and we do that all the time. Since CRC32 is very easy to crack (defining crack as forcing a ROM to get any wanted CRC32 value by modifying 4 bytes), we have already seen people (lamers) modifying romsets, cracking the CRC so that it matches the original one, and distributing them. Raflsaiu is not a problem since we know
the correct ROMs don't exist, but if anybody did the same with some existing romsets, it would become impossible (read: very hard and painful) for us to identify which is the correct romset, since the _only_ automated thing we use is CRC.

Now, MD5 has been already cracked as well, no matter if the Unix/Linux world has adopted and advertised it for some reason. It might not be just as trivial as CRC, but there are known attacks to crack it. The only safe hash algorithm to date seems to be SHA-1, which I strongly suggest for MAME.

Sometime in the future, MAME will probably add SHA-1 as a file signature checking method. 😀

"I see a little silhouette-o of a man, Scaramouche, Scaramouche, will you
do the Fandango!" - Queen

Stiletto

Reply 1 of 5, by DosFreak

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Yawn

I prefer PowerArchiver's .cab personally...but different compression method's are better for different things. I use rar & .cab for my backup's.... .cab beat's out .rar mostly but in some cases rar wins.

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Reply 2 of 5, by Snover

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Is that a "Normal" compression or a "Maximum" compression? I always found CAB files give pretty crappy compression ratios.
The best I think I ever found was LHA/LZH, which is (or was) used largely in Nihon [Japan]. ACE generally works better than RAR, and bzip2 generally works better than most of them (however, I haven't done many tests with ACE because I don't actually HAVE WinACE -- one compression program is enough for me, thanks). I can't vouch for 7zip. However, LZMA sounds like it uses the same (or simlar) compression technique as LHA/LZH (Lempel/Ziv/Huffman) -- most likely Lemphel/Ziv plus some other dude and "archive". In any case, it seems to me that the best compression could be achieved by creating a format that incorporated many different aspects -- lossless images => PNG, images acceptible to be lossy => JPG, animations => MNG or AVI -- basically just getting rid of all of the uncompressed crap (Targa, PCX, Bitmap). Similarily, using LAME --r3mix -q0 for audio would work wonders -- it's preceptually lossless and still does a damn good job of it. Vorbis would be even better, but it hasn't been fully tested yet so I can't really recommend it. Yet. Anything else...text files, other strange data resources (don't ask me what, since computers can output three things: visual, aural, and more recently "touch" data) could be compressed using whichever format worked the best for compressing, y'know, text or whatever. But then, that's just a dream of mine, and one that's already been at least partially accomplished with MP3 packing utilities from CLASS and other cracking groups, but one that will never really be a reality. (Said CLASS utility would be useful if it was used legally and if it was openly modifiable and if Fraunhofer didn't want to charge $0.75 per decoder now.)
Anyway, whee.

My personal solution to most things like this is to make less bulky shit. 😄 [Vector data, well-written code *cough,ahhem*, no !@#$ raster data]

Oh, and SHA-1? LET'S GET THOSE DISTRIBUTED.NET BOXEN ON IT! Honestly though, CRC32 and MD5 generally work well enough, since all they're being used for is the verification of versions, really, and not for critical, possibly malicious data. I mean anything could be malicious, but, y'know, WHY?

Yes, it’s my fault.

Reply 3 of 5, by Stiletto

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Off-Topic: For the record, I checked through my DOS4GW's last night. I'd forgotten that along the way I'd been updating them with newer versions, to no ill effect. I'm unable to see what really came with the games without reinstalling them, so while I had 10 copies of dos4gw.exe, 6 of them were the same CRC as 1_97_2.exe, and the rest were 1_97.exe. But I think, now, I'll change them all to ver 2.01a. 😀

"I see a little silhouette-o of a man, Scaramouche, Scaramouche, will you
do the Fandango!" - Queen

Stiletto

Reply 4 of 5, by DosFreak

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Bump.

Man these forums are DEAD. 🙁

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Reply 5 of 5, by Snover

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You say that, but then realise that I'm still getting three or four new users signing up every day. (Not that they post, but...)

Besides, it seems only the regulars or near-regulars pay any attention to anything other than getting their own problems solved.

Yes, it’s my fault.