DOS ain't dead - DOS/32a: utility to extract Linear Compressed (LC) files?

Zyzzle

28.09.2022, 00:38

DOS/32a: utility to extract Linear Compressed (LC) files? (Users)

The DOS/32 Advanced extender is a great replacement for DOS4G/w, but files compressed with its SC compressor utility can't be decompressed (easily). Unfortunately, the SC utility is a very bad compressor. UPX greatly outperforms and offers much, much tighter compression, *and* can decompress the produced executables.

Is there any utility or program that can easily decompress the compressed DOS/32a executables? My aim is to recompress these executables in order to save ~30-50% disk space over the inefficient compression which SC.EXE offers. The claim is that such LC files are "unextractable" but I'm sure someone has found a way. I've looked and can find no such utility, however, but perhaps I missed it back in the day?

Guti

28.09.2022, 07:20

@ Zyzzle

DOS/32a: utility to extract Linear Compressed (LC) files?

Post reply

> The DOS/32 Advanced extender is a great replacement for DOS4G/w, but files
> compressed with its SC compressor utility can't be decompressed (easily).
> Unfortunately, the SC utility is a very bad compressor. UPX greatly
> outperforms and offers much, much tighter compression, *and* can decompress
> the produced executables.
>
> Is there any utility or program that can easily decompress the compressed
> DOS/32a executables? My aim is to recompress these executables in order to
> save ~30-50% disk space over the inefficient compression which SC.EXE
> offers. The claim is that such LC files are "unextractable" but I'm sure
> someone has found a way. I've looked and can find no such utility, however,
> but perhaps I missed it back in the day?

Just as an OT, it seems that official site for DOS32/A is dead: https://dos32a.narechk.net/

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Laaca

Czech republic,
28.09.2022, 08:13

@ Guti

DOS/32a: utility to extract Linear Compressed (LC) files?

Post reply

> Just as an OT, it seems that official site for DOS32/A is dead:
> https://dos32a.narechk.net/

I see. But it is still on the GitHub.
https://github.com/abbec/dos32a

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roytam 28.09.2022, 10:42 @ Laaca	DOS/32a: utility to extract Linear Compressed (LC) files? Post reply
	> > Just as an OT, it seems that official site for DOS32/A is dead: > > https://dos32a.narechk.net/ > > I see. But it is still on the GitHub. > https://github.com/abbec/dos32a >About >Source for the DOS32a extender (not official)

CandyMan 28.09.2022, 11:09 @ roytam	DOS/32a: utility to extract Linear Compressed (LC) files? Post reply
	You can find the source code for DOS32A here: https://github.com/amindlost/dos32a Among other things, there is SD (SunSys Debugger - see "sloadlc.asm" file - which loads LC compressed files into memory).

Zyzzle 30.09.2022, 05:58 @ CandyMan	DOS/32a: utility to extract Linear Compressed (LC) files? Post reply
	> You can find the source code for DOS32A here: > > https://github.com/amindlost/dos32a > > Among other things, there is SD (SunSys Debugger - see "sloadlc.asm" file - > which loads LC compressed files into memory). Thank you! This pointer helped immensely. sloadlc.asm is exactly what I wanted.

RayeR

CZ,
15.12.2022, 16:16

@ Zyzzle

DOS/32a: utility to extract Linear Compressed (LC) files?

Post reply

> This pointer helped immensely. sloadlc.asm is exactly what I wanted.

Well, did you managed to make a unpacker of it? It may come handy so I'm interested.

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Zyzzle

20.12.2022, 06:25

@ RayeR

DOS/32a: utility to extract Linear Compressed (LC) files?

Post reply

> > This pointer helped immensely. sloadlc.asm is exactly what I wanted.
>
> Well, did you managed to make a unpacker of it? It may come handy so I'm
> interested.
I managed only to load the (compressed) LC files into the SD debugger, but could not dump the contents of these (uncompressed) files to disk, as SD.exe froze my system.

Attempting to compile sloadlc.asm file didn't work for me in TASM, either. I got compiler errors which I couldn't circumvent or correct.

So, I gave up. It's obviously possible to load compressed LC files into SD.exe, but some versions I tried of SD.exe said "Compressed LC-files are not supported". This error occurred in the latest official release (DOS32/A SD v9.1.2), but not on the version of SD.EXE included in DOS/32A v7.35 at: https://sourceforge.net/projects/dos32a/files/

So, somehow latest version of SD was castrated in v.9.1.2. Perhaps source of sloadlc.asm is incompatible, which explains my errors in trying to compile just it into a simple dumper to disk of the uncompressed data file. Rebuilding relocations, and rewriting a new, valid .EXE file and header.

The sample file I'm trying to decompress is QV.EXE included in Quickview v. 2.61 package. (This loads fine into v. 7.35 SD, but v. 9.1.2 SD refuses saying it "LC files are not supported in this version). This is for sole purpose of recompressing it by UPX to save much more diskspace over very inefficient SC.EXE (non-LZ77 compressor).

Could you make further progress?

Berlin, Germany,
22.12.2022, 21:43

@ Zyzzle

DOS/32a: utility to extract Linear Compressed (LC) files?

Post reply

> The sample file I'm trying to decompress is QV.EXE included in Quickview v.
> 2.61 package. (This loads fine into v. 7.35 SD, but v. 9.1.2 SD refuses
> saying it "LC files are not supported in this version). This is for sole
> purpose of recompressing it by UPX to save much more diskspace over very
> inefficient SC.EXE (non-LZ77 compressor).

Did you already try to reach QV author Wolfgang Hesseler?

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Zyzzle

23.12.2022, 10:44

@ rr

DOS/32a: utility to extract Linear Compressed (LC) files?

Post reply

> > The sample file I'm trying to decompress is QV.EXE included in Quickview
> v.
> > 2.61 package. (This loads fine into v. 7.35 SD, but v. 9.1.2 SD refuses
> > saying it "LC files are not supported in this version). This is for sole
> > purpose of recompressing it by UPX to save much more diskspace over very
> > inefficient SC.EXE (non-LZ77 compressor).
>
> Did you already try to reach QV author Wolfgang Hesseler?

Yes, I did try successfully, and reached him a few years ago (2018 or so), and he was not interested in releasing a UPX'ed version of Quickview. Or, at least did not indicate it would be in his best interests, since it is "harder" to extract / decompress the LC executables, there being no built-in extractor. He was a very nice fellow. So, I tried -- merely for educational use, mind you, to find a way to make such version myself, since UPX (lzma compression) yields in general about ~30 to 50% smaller .EXE than the compressed files produced by DOS 32/A SC.EXE. My intention being to create very small, optimized portable DOS with Quickview player which will fit on floppy disk.

My goal merely being to create smallest-possible binaries by recompressing these LC files. Another example is the MPXPLAY.EXE executable, which is also compressed by LC.exe, and that is a totally donation-based project. I did not try contacting PDFSoft author, however.

Guti

29.09.2022, 13:22

@ Laaca

DOS/32a: utility to extract Linear Compressed (LC) files?

Post reply

> > Just as an OT, it seems that official site for DOS32/A is dead:
> > https://dos32a.narechk.net/
>
> I see. But it is still on the GitHub.
> https://github.com/abbec/dos32a

Yes, but this is only a fork. Not the official project.

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