My 8086 DOS heatshrink uses (segmented inicomp depacker, single-segment help page depacker, streaming ELD library depacker)

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Hi, I wanted to let you know I am using the heatshrink compression format for several parts of my 86 DOS debugger project, lDebug (that's an L).

The first use was in inicomp, my executable depacker for triple-mode executables (DOS kernel, DOS device driver, DOS application). The heatshrink format is used as one of many options. This depacker supports compressed as well as uncompressed data sizes beyond 64 KiB, using 8086 segmented addressing in Real/Virtual 86 Mode. Other than that, it is special in that the destination buffer is always below the source and it is valid for the destination to partially overwrite the source if the source pointer is always above-or-equal the destination pointer. That means the entire data must be stored in memory, but less memory than the full source + full destination is needed.

The second use is for lDebug help pages. This is ready, but not yet used by default. The help pages always fit within less than 64 KiB so most of the segmentation things have been taken out of this one. It comes with a stand alone test program which uses a 256-byte file buffer to hold parts of the source file.

The third use is for the Extensions for lDebug packed library executable.
I wrote some about the latest use on my blog. Like the help page depacker this uses a 256-byte file buffer for the compressed input. It also has a stand alone test program; this one supports input and output files > 64 KiB too.

Unlike the other two depackers, this one uses a 4 KiB circular decompression buffer (thus window size must not be > -w 12), and the implementation of its put_file_data will grab data after a certain depackskip counter reaches zero. The compressed data stream is much larger than 64 KiB, but only the output data of interest is grabbed by put_file_data. If that function has filled its output buffer, it will pause the current depack call. A paused depack call can be resumed when more data is needed from later on in the decompressed data stream. To implement the pausing and resumption, I run depack on its own stack separate from the main application's, and I save all needed working registers on either stack when switching stacks.