tANS Codec

The Tans codec implements tabled Asymmetric Numeral Systems (also known as Finite State Entropy or FSE).

Theory

tANS provides the near-optimal compression ratios of arithmetic coding with the speed of a table-lookup decoder (similar to Huffman). It models symbol probabilities into a finite state machine where state transitions consume fractional bits.

Like rANS, it uses length-prefix framing and supports a TAG_RAW raw-fallback mechanism. If the data is incompressible, or if the tANS headers would expand the payload, it writes the original bytes directly.

Usage

The codec is a peer of rANS and Huffman and is automatically trialed by the compressor's dispatcher to find the optimal coder for a given plane.

References

• Jarek Duda, "Asymmetric numeral systems: entropy coding combining speed of Huffman coding with compression rate of arithmetic coding" (2013). Link