Finite State Coder

This project is an experimental implementation of Jarek Duda's assymetric numeral systems (ANS), as described in the following paper:

http://arxiv.org/abs/1311.2540

To understand ANS, i extensively used the FSE project:

https://github.com/Cyan4973/FiniteStateEntropy

by Yann Collet, which is referenced by Jarek's paper. See the blog entry: http://fastcompression.blogspot.fr/2013/12/finite-state-entropy-new-breed-of.html

Fabian Giesen also has interesting implementations ideas. See his blog for pointers:

http://fgiesen.wordpress.com/

Code is located here: https://github.com/rygorous/ryg_rans I re-implemented some his ideas (Alias method, interleaving, etc.) for experimentation purpose.

---

The word-based coding methods (CODING_METHOD_16B and up) will use b=2^16 and write 16b-words at a time. They also have variants with interleaving and alias method.

The default CODING_METHOD_16B_4X is the fastest so far, but experimentation is still underway...

---

The other implementations (CODING_METHOD_BUCKET, etc.) use bit-by-bit encoding/decoding, or byte-by-byte, where bits are grouped in packets of 8bits. Note that the coder still emits bits one by one though (b=2, in the ANS terminology).

There are several 'Spread Function' available to try different symbol <-> slots assignments (see BuildSpreadTableXXX() functions). You can switch from one to another in the command line (-buck, -mod, etc.)

Known limitations:

• alphabet size should be <= 256
• max table size is 2 ^ 14

---

Command line help:

./fsc -h
usage: ./fsc [options] < in_file > out_file
options:
-c           : compression mode (default)
-d           : decompression mode
-s           : don't emit output, just print stats
-l           : change log-table-size (in [2..14], default 12)
-w                 : use word-based coding.
-w2                : use word-based coding 2x interleave.
-w4                : use word-based coding 4x interleave.
-a                 : use word-based coding + alias.
-a2                : use word-based coding + alias + interleave.
-mod               : use modulo spread function
-rev               : use reverse spread function
-pack              : use pack spread function
-buck              : use bucket spread function
-h           : this help

./test -h
usage: ./test [options] [size]
options:
-t <int>           : distribution type (in [0..5])
-p <int>           : distribution param (>=0)
-s <int>           : number of symbols (in [2..256]))
-l <int>           : max table size bits (<= LOG_TAB_SIZE)
-save <string>     : save input message to file
-d                 : print distribution
-f <string>        : message file name
-w                 : use word-based coding.
-w2                : use word-based coding 2x interleave.
-w4                : use word-based coding 4x interleave.
-a                 : use word-based coding + alias.
-a2                : use word-based coding + alias + interleave.
-mod               : use modulo spread function
-rev               : use reverse spread function
-pack              : use pack spread function
-buck              : use bucket spread function
-h                 : this help

./bit_test -h
usage: ./bit_test [options] [size]
-l <int>           : max table size bits for bit-by-bit
-l8 <int>          : max table size bits for byte-by-byte
-p <int>           : try only one proba value
-fsc               : skip FSC
-fsc8              : skip FSC8
-w                 : use word-based coding.
-w2                : use word-based coding 2x interleave.
-w4                : use word-based coding 4x interleave.
-a                 : use word-based coding + alias.
-a2                : use word-based coding + alias + interleave.
-mod               : use modulo spread function
-rev               : use reverse spread function
-pack              : use pack spread function
-buck              : use bucket spread function
-h                 : this help