On at 2023-09-01 19:03 +0200, Bernd Böckmann via Freedos-devel wrote:
Well, I think it's me to blame ;-)
I will try to build some compression mechanism into AMB, so that the
help files get smaller. The main FreeDOS help file would also benefit
from that, I think.
Bernd
I recently added one of my executable compression formats to my
debugger's online help, allowing it to "assemble" (build) the help pages
at build time and then compress them before inclusion (by NASM incbin
directive) into the main assembly pass. Perhaps you want to copy parts
of this.
I used the heatshrink library, "A data compression/decompression library
for embedded/real-time systems." [1]. It is available under the ISC
License [2]. I created two different depackers, both under the Fair
License (but feel free to use and copy these under any usage
conditions). One is the executable depacker, which can deal with data
(both compressed and decompressed) exceeding 64 KiB, using 8086
segmented addressing [3]. The other is a bit smaller and assumes that
all data fits in a single segment each, though the source and
destination can be in different segments [4].
For the recent lDebug release 6 I did not yet enable these build
options, although everything is implemented for the in-memory online
help to be largely compressed. I'm compressing each help page as its own
data block, unrelated to one another. Despite this, almost all of the
data does compress down by 20% to 60%. (In heatshrink use, the
percentage indicates how much of the uncompressed size is dropped to
reach the compressed size.)
The depacker needs about 300 bytes in my application (for only the
memory-to-memory depacker). The compression is done in a loop at build
time [5]. I try every -w parameter from 10 to 14 and every -l parameter
from 4 to 14 (but -l must be below -w), and use the best result.
(Usually -w 10 -l 4.) (I just found that the valid ranges for the
parameters are actually larger than this, still testing how well those
work.) I use a slightly modified compressed file format, in which the
first byte is the -w parameter and the second byte is the -l parameter,
and then the original compressed data file is appended. The depacker
needs to know the packed size to know when to end depacking. In my
debugger's depacker, I append a NUL byte at the end for the user to know
how long the unpacked data is, but this could be modified easily to
return the size.
Regards,
ecm
[1]: https://github.com/atomicobject/heatshrink
[2]:
https://github.com/atomicobject/heatshrink/blob/7d419e1fa4830d0b919b9b6a91fe2fb786cf3280/LICENSE
[3]: https://hg.pushbx.org/ecm/inicomp/file/41860de1db0e/heatshr.asm
[4]:
https://hg.pushbx.org/ecm/ldebug/file/654bf2cbfffb/source/hshrink.asm#l208
[5]: https://hg.pushbx.org/ecm/ldebug/file/654bf2cbfffb/source/mak.sh#l309
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