Aart's Blog

I just posted version 1.5 of Chess, Checkers, and Reversi for Android at the Android Market , all with the much requested "save on exit" feature. If a user exits a game in progress, the game is automatically saved and later restored when the application is restarted. Even if the interrupt happened while the engine was thinking about its move, the game will restart in that state (albeit taking the full allocated time again). Apologies to all users who have been requesting this feature for a while, I just needed to find some time for it.

With tears in my eyes I read the news and watched the pictures of the senseless attack on the Dutch royal family by a man who crashed his car through the crowd during the annual Queen's Day celebration. I pray for the victims and those who mourn.

Version 1.4 of Chess for Android is now available at the Android Market with the following new features: Two improvements in the engine: removed unnecessary restriction on search depth and fixed bug that could cause an out-of-bounds exception. The engine now detects draw by a simplified form of three fold repetition. The detection is not complete, since only limited game history is kept; but at least this new feature avoids some very annoying repetitions. Draw by the fifty move was already implemented. A new level "Auto-play" has been added (press the Menu button). If this level is selected, then the next time the engine takes control (make either a move or touch "Reverse sides"), the game is played automatically.

Due to all Android distractions, it has been a while since I posted on BikJump. It recently ended at a somewhat disappointing 54th place in OpenWar 5th Edition . Version 2.01 is now playing in the final of the 5th Division WBEC Ridderkerk edition 16 .

I ported the Java source code of the engine in Checkers for Android into C++ and implemented the parts required to form a plug-in engine for Martin Fierz' CheckerBoard application. The result is BikMove (with an obvious wink to my UCI chess engine BikJump). I also added the ability to query checkers endgame databases based on Martin Fierz' probing code (used with his kind permission). The main features of BikMove are listed below: Checkerboard compliant checkers engine. Iterative deepening, alpha-beta pruning. Queries endgame databases during search. The engine needs some more work to become competitive with others checkers engines, but it already plays what looks to me like decent checkers. Give it a try if you are interested!

As can be seen in previous postings, the perft method is useful to verify the correctness of a move generator. The method traverses the game tree up to various, increasing depths to count all leaf nodes. The results are compared with pre-computed values to isolate bugs. Although the method originated in the chess programming community, the same debugging principle can be used for any board game with deterministic rules. So far, I have used perft to verify the move generation of Chess for Android and, thanks to Martin Fierz , also for Checkers for Android. I was unable to find pre-computed perft numbers for reversi, however. Therefore, here is what is probably the debut of perft for reversi from the initial position, hopefully useful data for aspirant reversi programmers (at depths 9 and up, "passing" moves start to occur; at depths 11 and up, higher leaf nodes in which neither player can move start to occur). DEPTH #LEAF NODES ======================== 1 ...

I was able to make a small improvement in the checkers move generator (written in Java for the Android SDK). The following table shows run times of several perft depths before and after optimization when run on the emulator (which should mimic actual run times on the phone quite well). DEPTH #LEAF NODES ORIGINAL OPTIMIZED TIME TIME ==================================== 7 179740 2.9s 1.9s 8 845931 14.2s 9.7s 9 3963680 66.3s 45.6s 10 18391564 294.6s 208.7s P.S. Runtimes for a C++ checkers move generator on a 2.2 GHz Core 2 Duo are given at my checkers page .

Martin Fierz kindly extended his engine Cake with a perft feature. Luckily the numbers reported by Cake match the numbers reported by Checkers for Android exactly. Below the numbers from the start position are shown, hopefully useful data for aspirant checkers programmers. DEPTH #LEAF NODES ======================= 1 7 2 49 3 302 4 1469 5 7361 6 36768 7 179740 8 845931 9 3963680 10 18391564 11 85242128 12 388623673

If you are looking for a checkers program for Windows, I can highly recommend Martin Fierz ' CheckerBoard , consisting of a checkers GUI that features game databases, opening books, endgame databases, and various checkers engines (including the capability to plug in your own as DLL). I have used his engine Cake as "sparring partner" to test the correctness and strength of Checkers for Android. Needless to say, Cake won, but the games at least assured me that my Android version plays correct checkers. Martin also kindly responded to my request for adding a perft feature to Cake, which will enable verifying the correctness of my move generator against his.

I am on the roll with updates! Version 1.3.2 of Chess for Android uses a larger font for the move list and highlights the last moved played by the engine (controlled by the already existing "show valid moves" button). I am thinking about a version 2.0 with a completely new board layout to use the limited screen space more effectively. As usual, keep an eye on this blog if you are interested.