fx-cmix

The fx-cmix is a updated implementation of fast-cmix.

Prize awarded on February 2, 2024. http://prize.hutter1.net/

Submission Description

This submission contains fallowing modifications on top of the recent fast-cmix Hutter Prize winner:

• paq8hp model is replaced with fxcmv1 model with fallowing notable additions:
  • Multiple state tables are used in predictors, this allows better predictability.
  • Most contexts are divided between 30 main predictors, this allows more efficient memory usage per context.
  • Added bracket, quote, first char, char in paragraph, column, table, template, word stream/paragraph context. These contexts are parsed depending on input, this includes parsing of wiki links, http links, tables, columns, paragraphs, quotes, brackets, list, templates.
  • Some contexts are swapped in predictors depending on what current input is (table, column mode, word/paragraph, list).
  • Some predictors are switched on/off depending on last char, link or current bracket which improves compression.
  • Predictions are mixed with context that are more aware of what predictors are outputting.
  • Match model (not present in paq8hp model).
  • Predictors are faster allowing more complex contexts.
• new dictionary
• small change in phda9 preprocessor and in two tables in cmix
• memory usage is larger in fxcmv1 model compared to old paq8hp

Below is the fx-cmix result:

Metric	Value
fx-cmix compressor's executable file size (S1)	436707 bytes
fx-cmix self-extracting archive size (S2)	112148343 bytes
Total size (S)	112585050 bytes
Previous record (L)	114156155 bytes
fx-cmix improvement (1 - S/L)	1.38%

Experiment platform
Operating system	Ubuntu 20.04
Processor	Intel(R) Xeon(R) CPU @ 2.20GHz Geekbench score 706
Memory	32 GB
Decompression running time	85 hours
Decompression RAM max usage	9575124 KiB
Decompression disk usage	~35GB

Time, disk, and RAM usage are approximately symmetric for compression and decompression.

Instructions

The installation and usage instructions for fx-cmix are the same as for fast-cmix.

One important note: it is recommended to change one variable in the source code for PPM. From line 26 in src/models/ppmd.cpp:

// If mmap_to_disk is set to false (recommended setting), PPM will only use RAM
// for memory.
// If mmap_to_disk is set to true, PPM memory will be saved to disk using mmap.
// This will reduce RAM usage, but will be slower as well. *Warning*: this will
// write a *lot* of data to disk, so can reduce the lifespan of SSDs. Not
// recommended for normal usage.
bool mmap_to_disk = true;

This variable is set to true by default, to comply with the Hutter Prize RAM limit.

Installing packages required for compiling fx-cmix compressor from sources on Ubuntu

Building fx-cmix compressor from sources requires clang-17, upx-ucl, and make packages. On Ubuntu, these packages can be installed by running the following scripts:

./install_tools/install_upx.sh
./install_tools/install_clang-17.sh

Compiling fx-cmix compressor from sources

A bash script is provided for compiling cmix-hp compressor from sources on Ubuntu. This script places the cmix-hp executable file named as cmix in ./run directory. The script can be run as

./build_and_construct_comp.sh

Running fx-cmix compressor

To run the cmix-hp compressor use

cd ./run
cmix -e <PATH_TO_ENWIK9> enwik9.comp

Running fx-cmix decompressor

The compressor is expected to output an executable file named archive9 in the same directory (./run). The file archive9 when executed is expected to reproduce the original enwik9 as a file named enwik9_restored. The executable file archive9 should be launched without argments from the directory containing it.

cd ./run
./archive9