Author Topic: Snapshot - WinAPE compression  (Read 1528 times)

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Offline CECPC

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Snapshot - WinAPE compression
« on: 15:40, 20 August 14 »
Hi!

I'm programming a utility based on SnapShot data.
I was used the info of this wiki (among others) about this format.

Format:SNA snapshot file format - CPCWiki

But WinAPE has an option to "compress" the data inside a V3 Snapshot.
I didn't find any info about this option.

This compression is different to SNZ implementation (a simple Gzip over a normal SNA).
Showing two snapshots, with and without compression, seems like some type of RLE implementation altough i don't know the specific implementation. Even
how to detect (except that size don't match) if the snapshot is compressed or not to avoid accept compressed snapshots.

Someone knows about it?
« Last Edit: 15:42, 20 August 14 by CECPC »

Offline Aeliss

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Re: Snapshot - WinAPE compression
« Reply #1 on: 18:36, 20 August 14 »
Something I have see in winape, if it s compressed Snapshot you have 2 things:
> offset 6b-6c = 0 (memory dump size)
> chunk memory and the end of file.

MEM0 for Standard 64k.
MEM1 to MEM8 for memory expansion bank.

And yes it's RLE compression. The control byte is 0x0e5.

IDK how to explain clearely but for decompression
11 22 33 = 11 22 33
E5 03 11 = 11 11 11
E5 00 = E5

And for compression 11 11 = 11 11 and not E5 02 11
« Last Edit: 18:59, 20 August 14 by Aeliss »

Offline Aeliss

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Re: Snapshot - WinAPE compression
« Reply #2 on: 18:49, 20 August 14 »
****
Wrong manipulation, there is nothing to delete post ?
« Last Edit: 18:50, 20 August 14 by Aeliss »

Offline TFM

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Re: Snapshot - WinAPE compression
« Reply #3 on: 22:51, 20 August 14 »
****
Wrong manipulation, there is nothing to delete post ?


No sadly not, we had that in the good old days, but  :-\
TFM of FutureSoft
Also visit the CPC and Plus users favorite OS: FutureOS - The Revolution on CPC6128 and 6128Plus

Offline CECPC

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Re: Snapshot - WinAPE compression
« Reply #4 on: 10:41, 21 August 14 »
Argh. I'm dumb. I though that the chunk part was for CPC+ only.

Sorry. I promise to RTFM better next time.

Offline TFM

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Re: Snapshot - WinAPE compression
« Reply #5 on: 18:49, 21 August 14 »
Sorry. I promise to RTFM better next time.


RTFM... here... ReadTheFutureosManual...



TFM of FutureSoft
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Offline Executioner

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Re: Snapshot - WinAPE compression
« Reply #6 on: 03:05, 27 August 14 »
Yes, Aeliss has the compression algorithm correct. It's simple RLE with E5 control byte, exactly as posted above.