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59 lines
2.5 KiB
Markdown
59 lines
2.5 KiB
Markdown
# Upkr
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Upkr is a simple general purpose lz packer designed to be used in the [MicroW8](https://github.com/exoticorn/microw8) platform.
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The compressed format is losely based on [Shrinkler](https://github.com/askeksa/Shrinkler) with the main difference being that
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Upkr doesn't differentiate between literals at odd or even addresses (by default) and that I went with rANS/rABS instead of a range coder.
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Compression rate is on par with Shrinkler.
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The differences compare to Shrinkler also makes it interesting on 8bit platforms. The z80 unpacker included in the release
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is both about twice as fast and smaller than the Shrinkler unpacker.
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## Inspirations:
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* Ferris' blog about his [C64 intro packer](https://yupferris.github.io/blog/2020/08/31/c64-4k-intro-packer-deep-dive.html)
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* [Shrinkler](https://github.com/askeksa/Shrinkler)
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* Ryg's [sample rANS implementation](https://github.com/rygorous/ryg_rans)
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## Unpackers
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The release includes a reference c unpacker, as well as some optimized asm unpackers (arm and riscv). The unpckers in
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c_unpacker and asm_unpackers unpack the default upkr compressed format. The z80_unpacker
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is based on some variations to the compressed format. (Use `upkr --z80` to select those variations.)
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An optimized x86 (DOS) unpacker is currently being worked on out of tree.
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## Usage
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```
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upkr [-l level(0-9)] [config options] <infile> [<outfile>]
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upkr -u [config options] <infile> [<outfile>]
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upkr --margin [config options] <infile>
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-l, --level N compression level 0-9
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-0, ..., -9 short form for setting compression level
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-u, --unpack unpack infile
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--margin calculate margin for overlapped unpacking of a packed file
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Config presets for specific unpackers:
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--z80 --big-endian-bitstream --invert-bit-encoding --simplified-prob-update -9
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--x86 --bitstream --invert-is-match-bit --invert-continue-value-bit --invert-new-offset-bit
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--x86b --bitstream --invert-continue-value-bit --no-repeated-offsets -9
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Config options (need to match when packing/unpacking):
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-b, --bitstream bitstream mode
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-p, --parity N use N (2/4) parity contexts
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-r, --reverse reverse input & output
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Config options to tailor output to specific optimized unpackers:
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--invert-is-match-bit
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--invert-new-offset-bit
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--invert-continue-value-bit
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--invert-bit-encoding
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--simplified-prob-update
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--big-endian-bitstream (implies --bitstream)
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--no-repeated-offsets
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--eof-in-length
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--max-offset N
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--max-length N
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```
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