Fathom

Fathom is a stand-alone Syzygy tablebase probing tool. The aims of Fathom are:

To make it easy to integrate the Syzygy tablebases into existing chess engines;
To make it easy to create stand-alone applications that use the Syzygy tablebases;

Tool

Fathom includes a stand-alone command-line syzygy probing tool fathom. To probe a position, simply run the command:

fathom --path=<path-to-TB-files> "FEN-string"

The tool will print out a PGN representation of the probe result, including:

Result: "1-0" (white wins), "1/2-1/2" (draw), or "0-1" (black wins)
The Win-Draw-Loss (WDL) value for the next move: "Win", "Draw", "Loss", "CursedWin" (win but 50-move draw) or "BlessedLoss" (loss but 50-move draw)
The Distance-To-Zero (DTZ) value (in plys) for the next move
WinningMoves: The list of all winning moves
DrawingMoves: The list of all drawing moves
LosingMoves: The list of all losing moves
A pseudo "principle variation" of Syzygy vs. Syzygy for the input position.

For more information, run the following command:

fathom --help

Programming API

Fathom provides a simple API. There are three main function calls:

tb_init initializes the tablebase
tb_probe_wdl probes the Win-Draw-Loss (WDL) table for a given position
tb_probe_root probes the Distance-To-Zero (DTZ) table for the given position.

All of the API functions use basic integer types, i.e. there is no need to create and initialize data-structures. Fathom does not require the callee to provide any additional functionality (e.g. move generation) unlike the traditional tbprobe code. However, chess engines can opt to replace some of the functionality of Fathom for better performance (see below).

Chess Engines

Chess engines can be tb_probe_wdl to get the WDL value during search. The tb_probe_root functional can be used to help pick the best move at the root. Note that tb_probe_root is slower and therefore should only be used at the root.

Chess engines can opt for a tighter integration of Fathom by configuring tbconfig.h. Specifically, the chess engines can define TB_*_ATTACKS macros that replace the default definitions with the engine's own definitions, avoiding duplication of functionality.

Credits

The Syzygy tablebases were created by Ronald de Man. Much of the probing code tbprobe.c is a modified version of Ronald's tbprobe.cpp for Stockfish (all Stockfish-specific code has been removed). The tbcore.c file is virtually unchanged from Ronald's original version.

License

Ronald de Man's original code can be "redistributed and/or modified without restrictions".

The new modifications are released under the permissive MIT License:

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

bsamseth / Fathom