andor-kesselman/carballo

Carballo Chess Engine

Carballo Chess Engine

Carballo (the galician word for Oak, it's all about search trees) is an Open Source Java chess engine with two interfaces:

• UCI: a text interface for chess GUIs like Arena: https://github.com/albertoruibal/carballo/raw/master/carballo-uci-1.3.tgz
• HTML5: developed with Google Web Toolkit (GWT) using the Vectomatic SVG library: http://www.mobialia.com/webchessgwt

It is organized into modules:

• Core: the chess engine
• Jse: the Java Standard Edition version with the UCI interface and JUnit tests
• Gwt: components needed for the GWT GUI
• GwtGui: an HTML5 interface developed by Lukas Laag, it depends on Core and Gwt
• Applet: the applet code (deprecated), it depends on Core and Jse

The Core and the UCI interface are converted to C# in the project http://github.com/albertoruibal/carballo_cs

It is licensed under GPLv3 and the source code is hosted at https://github.com/albertoruibal/carballo. You are free to use, distribute or modify the code, we ask for a mention to the original authors and/or a link to our pages.

Features

• UCI interface for chess GUIs like Arena
• It includes a great GWT interface by Lukas Laag and a deprecated Java Applet GUI
• Based on bitboards with a magic bitboard move generator, it also includes code for magic number generation
• Move iterator sorting moves with four killer move slots, SEE, MVV/LVA and history heuristic
• PVS searcher
• Aspiration window, moves only one border of the window if falls out
• Transposition Table (TT) with zobrist keys (it uses two zobrist keys per board to avoid collisions) and multiprobe
• Quiescent Search (QS) with only good or equal captures (according to SEE) and limited check generation
• Internal Iterative Deepening to improve sorting
• Extensions: Check, pawn push, passed pawns, mate threat and singular move
• Reductions: Late Move Reductions (LMR)
• Pruning: Null move Pruning, static null move pruning, futility pruning and aggressive futility pruning
• Pluggable evaluator function, distinct functions provided: the Simplified Evaluator Function, other Complete and other Experimental
• Parameterizable evaluator (only for the complete & experimental evaluators)
• Selectable ELO level with an UCI parameter
• Supports Chess960
• Polyglot opening book support; in the code it includes Fruit's Small Book
• FEN notation import/export support, also EPD support for testing
• JUnit used for testing, multiple test suites provided (Perft, BS2830, BT2630, LCTII, WinAtChess, etc.)

Test results in my Intel Core i7-3667U CPU @ 2.00GHz:

Test suite	Time per position	Version 1.3	Version 1.2
WinAtChess (New)	1 second	288/300	287/300
SilentButDeadly	1 second	116/134	90/134
ECMGCP	10 seconds	131/183	130/183
Arasan	60 seconds	26/250	19/250

His real strength is about 2400 ELO points, you can check his tournament rankings at http://www.computerchess.org.uk/ccrl/

Authors

• Alberto Alonso Ruibal: http://www.alonsoruibal.com
• Lukas Laag, developer of a great GWT SVG library (http://www.vectomatic.org) and the Carballo GWT interface

Building

Carballo uses the Gradle build system, you can get Gradle from http://www.gradle.org

Build all the jars and install them to your local Maven repository:

gradle install

Build the UCI interface:

cd jse
gradle proguard

Build the GWT interface:

cd gwtgui
gradle compileGwt

Testing

Run fast tests:

gradle fastTest

Run the "Win at Chess" test suite:

cd jse
gradle -Dtest.single=WinAtChessTest cleanTest test

Run Silent but Deadly tests:

cd jse
gradle -Dtest.single=SilentButDeadlyTest cleanTest test

History

Version 1.3: A lot of work in the evaluation function for a better positional play

• Now AttacksInfo holds the attacks information by piece type
• This allows to improve mobility and king safety evaluation detecting squares attacked by less valuable pieces
• Removed the king defense bonuses from the Experimental evaluator
• New MOBILITY array holding mobility bonuses by piece type and number of destiny squares
• Simplified the Bishop's Capablanca rule
• Removed some rook in 7th rank logic
• Improved the pawnCanAttack squares detection removing squares that cannot be reached due to opposite pawns
• Fixed the unsupported pawn penalty
• Modify the "rook attacks backward pawn logic" to detect real backward pawns
• Evaluation refactoring using the "W" and "B" constants and the "us" and "them" variables
• The Attacks evaluation is now done in a separated evalAttacks() method, unifying the attack bonuses in the PAWN_ATTACKS, MINOR_ATTACKS and MAJOR_ATTACKS arrays
• Piece value constants moved to the Config class and removed the PIECE_VALUES array
• Better midgame-to-endgame evaluation scaling with the new NON_PAWN_MATERIAL_MIDGAME_MAX and NON_PAWN_MATERIAL_ENDGAME_MIN constants
• Remove some UCI parameters and change them by constants for a better running optimization

Version 1.2: A new MoveIterator, Chess960 and lots of UCI improvements

• New MoveIterator that generates only legal moves with a check flag set
• Added support for Chess960 (Fischer Random Chess)
• Implemented UCI Ponder
• New replace strategy for the TT, taking into account the entry depth and the generation difference
• In the TT in QS, store the entries with checks generated with depth 1 and entries without checks with depth 0
• Four killer move slots
• Set default razoring margin to 400
• Fix the futility in QS and set the default futility in QS to 80
• Remove the null move margin and improve the null move reduction calculation
• Remove the recapture extension
• New time management strategy adding a "panic time" when the search in the root node fails low by a margin of 100
• Do not penalize pinned pawns in the evaluators, multiply the hung pieces bonus by the number of hung pieces, and pawn center opening corrections
• Fixed a bug multiplying the opening/ending values in the evaluators by negative factors
• Generate piece-square values in different classes
• Fixed an important bug in the SWAP algorithm for the SSE evaluation
• Now it uses 1" for the WinAtChess tests

Version 1.1: Urgent bug fix for 1.0

• The UCI interface was ignoring all the UCI options
• Do not allocate memory inside ExperimentalEvaluator.evaluate()
• Added the new pawn and endgame logic to the CompleteEvaluator (ExperimentalEvaluator continues as the default)

Version 1.0: Lots of fixes, small advances in test results: 294 in WAC (5") and 2520 in BT2630.

• New Transposition Table with a separated slot for the eval values
• Now uses the TT in quiescence search
• Fix mate values before inserting them in the TT, now the mate problems are solved with the right distance to the mate
• Fixes to futility pruning in quiescence search
• New pawn classification in the ExperimentalEvaluator
• Now the PV line is shown every time that a move is found in the root node
• Implemented UCI seldepth, lowerbound, upperbound and hashfull
• Implemented the depth and nodae limit for the search
• Enabled the endgame knowledge
• In the search, assume that pawn pushes are to the 6th, 7th or 8th rank
• Extend only checks with positive SSE
• Disable by default the recapture and pawn extensions, set the mate threat extension to one full PLY
• Fix recapture extension (now disabled by default)
• Tests migrated to the JUnit 4 format with annotations, and created a "fastTest" gradle task to run only the fast tests
• C# code separated in another GitHub project

Version 0.9: Fixes evaluator bugs

• Reordered some logic in the ExperimentalEvaluator
• Fixed a bug in the detection of the 2 bishop bonus
• Fixed another bug in the detection of candidate passer pawns
• Bug in the detection of the adjacent columns found by Yonathan Maalo
• Some improvements in the HTML5 interface

Version 0.8: Build system and GWT modifications

• Project build system migrated from Maven to Gradle
• Solved some evaluator bugs
• New option to do not use Magic Bitboard Attacks: optimizes start time in HTML5
• Removed specific Bitboard attacks code from GWT, can be simulated setting BitboardAttacks.USE_MAGIC = false
• New ArrayBufferBook for GWT, it can process any opening book loaded as a JS ArrayBuffer

Version 0.7: A small leap on the engine performance and a big code clean

• Code moved to Github
• Integrated ROOT, PV and NULL nodes search routine
• Activated singular movement extensions and changed default singular extension margin
• Do null move only when the remaining depth is > 3 PLY
• No not overwrite the value in the TT if there is no room
• Converted code to C# using sharpen. At the moment only the core of the engine
• Solved a big bug getting the move from the transposition table
• Also found another bug on the search getting the last captured piece value
• And the complete evaluator had a bug calculating the attacks value

Version 0.6: Source code reorganization, GWT and PGN improvements, no changes on the engine code

• Code splitted in carballo-core, carballo-jse and carballo-applet
• Carballo-core is GWT-friendly
• Integrated SAN notation on Board class
• Improved PGN export with SAN notation
• Added a GWT interface based on the one by Lukas Laag (http://vectomatic.org) code

Version 0.5: Improves about 150 ELO points over Carballo 0.4

• PVS searcher: SearchEngine completely changed
• Futility pruning now works!
• New TT algorithm, now also uses TT to store evaluation values
• Bug with draw detection with 3-fold repetition
• Bug with time management on tournament, was using the opponent's time amount
• Bug with history table overflow

Version 0.4: First version integrated with Mobialia Chess

• Parametrizable evaluator
• Evaluator changes