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Mr. Mouse
Registered: Dec 2001
Posts: 235 |
Warp compression method (AR)
Does anyone know the compression scheme used in Action Replay's "warp" disksaving method? I notice the sectors look a little different, where's the information about which next sector to go to while decompressing?
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
warp*25 uses a non standard sector format indeed... but no idea where to find info on it, could be interesting :) |
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Krill
Registered: Apr 2002
Posts: 2980 |
Which "compression" are you talking about? It's merely a custom disk format. As far as i remember, there is no sector link information - the sector layout is fixed. That is the reason why you can't have more than one warp file per track. |
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Mr. Mouse
Registered: Dec 2001
Posts: 235 |
What do you mean, no more than one file per track ? I've got several small ones that are on the same track. Okay, so I'd seen that one file was smaller after a warp save. Also the block contents are quite different compared to the non-warped saves. So what format is it in then? What is the order? I've noticed that on an empty disk the first normal files are started at track 17, the warped files start at track 1, sector 0. Suppose my file is smaller than oh 200 bytes. I won't need more than one sector. If I save several warped files of that small size, they each start in order, skipping 1 sector. So the first warped at sector 0, the next sector 2, then sector 4 etc.
Still, that leaves to find out for me how to read those sectors. Where do they start and in which direction does the reader go? And what process is used to alter the way the original bytes are represented. |
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tlr
Registered: Sep 2003
Posts: 1790 |
It looks to me like a warp saved track has the same layout as a normal dos track except for the contents of the data block.
Maybe the "compression" you see is that the t/s link is implied, thus giving two more bytes per sector free?
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rattus
Account closed
Registered: Oct 2002
Posts: 14 |
This might be actually quite interesting... Loading time for a warp file
was unbelievable in those days... Maybe usable in demos or so... |
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Mr. Mouse
Registered: Dec 2001
Posts: 235 |
The T/S link is not implied at all, in my view. Take a look at the first sector of a warped file. There are no immediate references to tracks or sectors. And the contents are really quite different from normal dos blocks. Try saving a small file on an empty disk, then warp-save the file and take a look at the BAM and sectors. You'll find the bytes in the warped sectors match nothing in the normal dos version. And that part interests me. What is happening, and how can I dissolve this. |
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Mr. Mouse
Registered: Dec 2001
Posts: 235 |
Here's an example file.
http://c64.xentax.com/downloads/warp_test.zip
There is an 8 byte file of values 01, 02, 04, 08, 10, 20 , 40, 80 (hex) stored at $1000.
And it's warped counterpart. |
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tlr
Registered: Sep 2003
Posts: 1790 |
Implied as in: the order is implicit i.e 0, 2, 4, 6, 8, etc...
I haven't checked the BAM yet.
Here's your first sector:
--- sync -----------------------
0000: ff ff ff ff ff
--- gcr ------------------------
0005: 52 54 b5 29 4b d2 b4 a5 55 55 55 55 55 55 55
--- decoded --------------------
0005: 08 01 00 01 a0 a0 0f 0f 0f 0f 0f 0f
--- interpretation -------------
sector header, t=1, s=0 (ID='$a0,$a0') chk=$01 (calc=$01)
--------------------------------
--- sync -----------------------
0014: 55 ff ff ff ff ff ff
--- gcr ------------------------
001b: 55 d4 ad a6 a9 69 49 d5 db 76 ab ca 52 95 a6 a6 a6 5d 76 ce 49 49 49 72
0033: 79 7b aa ab 6e 4e 53 99 4b 9d 4e 9a 96 9e a9 d6 ca b2 d2 b5 ae db c9 a6
004b: b3 d6 9b db 52 9a 72 bd 53 6b 73 4e 53 b5 bd d9 d9 5e 96 ad 53 52 a6 6d
0063: ad d3 7a a6 d6 6a ca 56 5d d6 9b 49 c9 66 ca 9e 96 ca aa cd 9d b3 ae 5e
007b: 9a db 5a c9 5b 93 d2 55 53 49 73 bb 6a b9 53 9b ba 6d 5b ad d6 4d 7b 4d
0093: 4a 4d 56 da ce 66 ca c9 4a 5d 9b b3 72 75 4d 6d da b2 66 d5 ce ae 72 9e
00ab: 5b 79 ce d5 d9 a6 75 49 d2 a5 6e 4e 52 9b d6 d2 5a b2 ba 55 ab aa b3 69
00c3: 5a d6 66 ad 7a b2 ab 4b 65 a9 95 69 56 52 96 4d 79 d6 d5 4e 5a 9b bb 73
00db: b2 49 5a 7b 7a b2 ab 4b 65 cd a6 ce 56 52 96 db 4e 9e ba 79 53 da 73 d2
00f3: cb 9e 53 66 66 52 ca 9d 4b 75 d6 d2 5d a6 7b 6e c9 d2 d6 b6 5a 79 b5 9e
010b: 93 56 ba 79 7a b2 ab 4b 65 cb 9a da 56 52 96 ce 4d 9e d9 5a 7a b2 ab 4b
0123: 65 a6 d2 cb 56 52 96 52 da 9e 4a ab 53 da 73 d2 6b 56 65 a9 a9 52 ca 9d
013b: 4b 75 d6 d2 5d a6 7b 6e c9 d2 d6 b6 5b 53 b9 9e 93 56 ba 79 7a b2 ab 4b
0153: 65 cb 9a da 56 52 96 ce 4d 9e 5e 9d 9d ff 4a 55 55 55 55 55
--- decoded --------------------
001b: 07 00 b8 f8 xx xx 16 b6 f5 xx xx xx xx xx ad 64
002f: xx xx xx 39 54 f0 6b 24 04 xx xx 04 30 18 d0 46
0043: 90 9c xx c4 b5 xx xx e6 35 cf xx 32 7f 86 xx a4
0057: 04 ab b6 49 1a 10 xx a2 xx 6a xx ba xx xx f2 26
006b: 17 18 62 48 xx xx xx 60 f1 xx xx d4 1a cc 66 68
007f: 14 8d xx 03 xx 9b 6a f9 04 cb xx 0b f7 xx ae ac
0093: 88 xx c6 64 xx xx 22 2d 34 97 xx 0c c7 c1 xx 6f
00a7: 9a xx xx 2b xx xx 16 xx 4f xx xx 14 89 88 7f 62
00bb: 10 91 xx c1 f0 96 26 66 xx 67 xx f1 8c 2a xx 18
00cf: 09 88 xx 19 ab xx xx xx 7c 9b xx 0a 5c d1 xx a1
00e3: xx xx c3 26 00 1c 63 xx 78 xx xx 33 a1 xx xx xx
00f7: xx xx xx 01 47 1c xx xx 5c xx xx 66 69 xx 3c xx
010b: 2c 11 xx 1a 60 xx 69 41 31 xx xx xx 99 xx d6 0a
011f: 50 90 62 xx xx xx 6f 22 29 8c xx 20 fc 8d xx e2
0133: cc xx 10 c8 01 xx a2 bf ab xx b8 3b cb xx xx f6
0147: 1c 8b xx xx 0a xx 2e f2 fc xx 12 xx b8 xx xx 64
015b: 86 xx xx xx xx xx 0f 0f 0f 0f
As you can see the header block is normal, but the data block uses a custom encoding. |
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tlr
Registered: Sep 2003
Posts: 1790 |
Quote: Here's an example file.
http://c64.xentax.com/downloads/warp_test.zip
There is an 8 byte file of values 01, 02, 04, 08, 10, 20 , 40, 80 (hex) stored at $1000.
And it's warped counterpart.
Warped files aren't storable on a d64 as it doesn't support bit level encodings. Please use g64 instead. |
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Mr. Mouse
Registered: Dec 2001
Posts: 235 |
http://c64.xentax.com/downloads/warptest_g64.zip
Okay, used g64. What tools do you use to view those, other than hex editors?
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