Scan 3.1 Copyright (C) 2015-2019 Fabien Letouzey.
This program is distributed under the GNU General Public License version 3.
See license.txt for more details.

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Today is 2019-07-06.
Scan is an international (10x10) draughts engine that uses the DamExchange Protocol (DXP) or text mode.  The name "Scan" comes from the scanning in evaluation that "divides" the board into 8 overlapping rectangles (2-26, 3-27, ..., 25-49) to judge positions.  Enjoy Scan!

Thanks to Harm Jetten for helping with Windows compatibility and compilation, testing, hosting, etc (you name it, he did it) ...  His engine, Moby Dam, is also cross-platform and open-source!

Thanks to Rein Halbersma for his expertise in draughts rules and implementation.

Thanks to RoepStoep and BumperBalloonCars for lidraughts.org!

Greetings to other game programmers; Gens una sumus.

Fabien Letouzey ([email protected]).

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Running Scan

In Windows terminology, Scan is a "console application" (no graphics).  Text mode is the default; a DXP mode is also available with a command-line argument: "scan dxp".  Scan needs the configuration file "scan.ini" (described below) and data files in the "data" directory (opening book, evaluation weights, and bitbases).  Note that, due to their size,  bitbases require a separate copy (from a previous version of Scan) or download for installation.

Most text-mode commands consist of a single letter (lower case):

0-2    -> number of computer players (e.g. 2 = auto-play)
(g)o   -> make the computer play your side
(u)ndo -> take back one ply
(r)edo -> replay a previous take-back, if no other move was played

time <n> -> fixed time limit; 10s by default

(h)elp -> find a few other commands

And of course you can type a move in standard notation.  Just pressing return can be used for forced moves.

A note about scores.   /- 89.xx means reaching a winning/losing endgame soon.   /- 99.xx means reaching the absolute end of the game soon.

Scan also has a Hub mode with a new protocol: "scan hub", which is used by the Hub GUI (separate download).  Programmers can use it to control Scan in an automated way; the description of the protocol can be found in "protocol.txt".

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Configuration

You can edit the text file "scan.ini" to change settings; you need to re-launch Scan in that case.  Here are the parameters.

variant: selects the rules to apply.  "normal" for international draughts.  However a lot of draws occur with those rules, even with somewhat weaker opponents.  "killer" (Killer draughts) and "bt" (breakthrough draughts: the first player who makes a king wins) are attempts to make the game more interesting at high level.  Scan should be very strong in Killer draughts and the "normal" rules are actually only supported as a legacy feature (sorry for the fans).  By contrast, BT support is experimental and not well tested.  IMPORTANT: changing the rules only makes sense if both players are aware of it (just like chess vs. draughts).

NEW variants: "frisian" and "losing" (aka antidraughts/giveaway/suicide).  To play Frisian draughts graphically, you will need Hub 2.1 (separate download); for other variants, upgrading is not necessary.  Just like for BT, losing draughts support is experimental and not well tested.

book, book-ply, book-margin: you can (de)activate the opening book here.  Randomness will only be applied to the first "book-ply" plies (half moves); subsequent moves will always be the best ones.  I used "book-ply = 4" during the Computer Olympiads.  "book-margin" acts as a randomness factor, for example: 0 = best move (for tournaments with pre-selected opening positions), 1 = small randomness (for serious games), 4 = fairly random (for casual games).  Note that equally-good moves are always picked at random, even after the first "book-ply" moves.  NEW: for Frisian draughts, I recommend larger values for book randomness; maybe "book-ply = 10" and "book-margin = 10".  If that's not enough, you can try larger values.

threads: how many cores to use for search (SMP).  Avoid hyper-threading (not tested).

tt-size: the number of entries in the transposition table will be 2 ^ tt-size.  Every entry takes 16 bytes so tt-size = 26 corresponds to 1 GiB; that's what I used during the Computer Olympiad.  Use smaller values for fast games.  Every time you increase it by one, the size of the table will double.

bb-size: use endgame bitbases (win/loss/draw only) of up to "bb-size" pieces (0 = no bitbases).  If you want maximum strength, use 6 (7 for BT variant, 5 for Frisian draughts).  This will take about 2 GiB of RAM though.  If Scan takes too much time to initialise or too much memory, select 5.  Note that bitbases require a separate copy (from previous versions of Scan) or download for installation into the "data" directory.

The other options are all related to the DamExchange Protocol (DXP), and are the same as in previous versions of Scan

dxp-server: for two programs to communicate, one has to be the server and the other one the client ("caller" to use a phone analogy).

dxp-host & dxp-port: dxp-host is the IP address (in numerical form such as 127.0.0.1) of the server to connect to (in client mode).  It has no effect in server mode.  dxp-port affects both modes.

dxp-initiator: in addition to client/server, one program has to start the games (initiator) and the other only answers requests (follower).  Scan's initiator mode is very basic.  It will launch an infinite match from the starting position, switching sides after each game.  Presumably other programs have a more advanced initiator mode and you should use that when possible.

dxp-time & dxp-moves: time control (only for the initiator).  Time is in minutes.  0 moves indicate no move limit: the game will be played to the bitter end (not recommended).

dxp-board & dxp-search: whether Scan should display the board and/or search information after each move.  Setting both to true, you can follow the games in text mode.  With both set to false, Scan is more silent.

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Compilation

The source code uses C  14 and should be mostly cross-platform.  I provided the Clang Makefile I use on Mac; it is compatible with Linux and GCC.  The source code is also known to work with Visual Studio.

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History

2015-04-10, version 1.0 (private release)

2015-07-19, version 2.0
- added opening book
- added endgame tables (6 pieces)
- added LMR (more pruning)
- added parallel search
- added game phase in evaluation
- added bitboard move generation
- added DXP

2017-07-11, version 3.0
- added Killer and BT variants
- improved evaluation
- improved QS (opponent-can-capture positions)
- improved speed
- improved bitbase probing (keep searching for an exact win after a BB win)
- improved Hub protocol (see protocol.txt)
- cleaned up code (stricter types and immutable position classes)

2019-07-06, version 3.1
- added Frisian and losing variants
- changed evaluation file format (but not the content)
- improved search (aspiration windows, singular extensions)
- simplified time management
- added optional node limit
- sped up bitbase loading
- allowed more than 20 pieces per side for compositions (not tested)
- cleaned up code (bitboard iterators and minor changes)