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lft
Registered: Jul 2007
Posts: 369 |
GCR decoding on the fly
Here's how to do it:
http://linusakesson.net/programming/gcr-decoding/index.php |
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HCL
Registered: Feb 2003
Posts: 728 |
@WVL: Yes i know about Doynax's packer. It was based on ByteBoozer, at least from the beginning, and optimized from there in all (?) possible ways. I'm just honored by his work :). ..and again, transferring while reading is a no-go if you want to be interruptable, and i would not sacrifice that. |
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Cruzer
Registered: Dec 2001
Posts: 1048 |
Quoting KrillMy experience with packing code has shown that it can indeed be sensible to pack code by separating op-code stream and operand stream. Clever!
Quote:For even better compression, make sure to actually add redundancy to the code (e.g., lda #$00:ldx #$00 is likely to pack better than lda #$00:tax in the end). That would cause bigger code, resulting in a potentially worse effect, so I would never do a thing like that.
The priority for a trackmo should be effect quality > loading time > file size. |
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Krill
Registered: Apr 2002
Posts: 2982 |
As i said, 4K.
But it really depends, there is no real loss in "lda #$00:ldx #$00" vs. "lda #$00:tax": same amount of cycles, just one byte more. The packed file is shorter with the former, the unpacked file longer. No problem. :) |
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WVL
Registered: Mar 2002
Posts: 903 |
Talking about that Doynax packer, I can't find it on CSDb.. Has it been released or is it just a few people that got it from Doynax himself? |
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Krill
Registered: Apr 2002
Posts: 2982 |
http://csdb.dk/forums/?roomid=11&topicid=59374#59404 -> http://doynax.googlepages.com/lz.zip .
Seems like he deleted his account, and before that never officially released the packer. Weird :\ |
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WVL
Registered: Mar 2002
Posts: 903 |
Whatever happened to him? :-( |
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Burglar
Registered: Dec 2004
Posts: 1105 |
http://sh.scs-trc.net/hereyougo/doynax_lz.zip |
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doynax
Account closed
Registered: Oct 2004
Posts: 212 |
First off, let me congratulate lft for an elegant solution and an entertaining write-up.
I have attempted to write a loader without an intermediate swizzling stage myself but could never manage it. This despite skipping the checksum, abusing the entire stack and zeropages as buffers, transmitting the resulting bit a whole bizarre order, and abusing every illegal opcode in the book.
Quoting KrillSeems like he deleted his account, and before that never officially released the packer. Weird : Oh, I'm still alive and lurking.
I rather lost interest after solving the technical problems but if anyone cares I'll put together a package with a bit of documentation plus binaries and "release" it somewhere reputable.
For the record it was designed to be easy to integrate into streaming loaders.
Personally I'm tempted to abandon D64 compatibility and try out Kabuto's beautiful 7-bit/byte GCR coder. I sort-of get the general idea but will really have to sit down with pen-and-paper to work out the finer details and convince myself that it really can code all inputs.
Anything to put off having to write actual game logic ;) |
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Fungus
Registered: Sep 2002
Posts: 691 |
I would love to see a proper release of your compressor doynax. |
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Dano
Registered: Jul 2004
Posts: 240 |
+1 for that! |
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