Aart's Blog

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.

Two minor updates at the Android Market . Version 1.3.1 of Checkers for Android has a slightly improved search and evaluation in the checkers engine. Some users complain the engine plays too strong, others say it is too weak. Needless to say I enjoy the challenge of making a strong engine more. I also added an "undo" feature for this game. Version 1.3 of Chess for Android now also has the option to disable highlighting all valid moves once a piece has been selected for more experienced chess players. I also modified the on screen button layout.

Version 1.3 of Reversi for Android at the Android Market adds an "undo" feature of the last move (to correct a mistake) and an option to disable the "ghost stones" for all valid moves (for users that prefer to see the board as in real-life).

I posted version 1.2.2 of Chess for Android at the Android Market that fixes a bug that would sometimes allow castling when no longer legal. I validated the move generator of the chess engine by doing a perft (an internal feature) on several board positions to minimize the probability of other bugs related to move generation.

I just posted version 1.2.1 of Chess, Checkers, and Reversi for Android at the Android Market with trackball support. A small circle denotes the trackball cursor, as illustrated in the screen shot below. Hopefully this will make the input easier. Many thanks to Chris Bueno for quickly testing the applications shortly after posting!

I received my own G1 (well, strictly speaking, the Android Dev Phone 1&#153)! This means now I can (1) read all user comments posted at the Android Market, and (2) experience my applications on the real device, rather than on the emulator. After just a few minutes I must agree with users stating that touch screen input is rather hard given the board size (something I could never experience on the emulator, where touch is emulated with mouse input). So, trackball support may be a good idea after all.