Since entering competition in May 1995, the chess program DARKTHOUGHT has participated in three ICCA world championships and two AEGON man vs. machine tournaments. Work on the program started about two years before its first tournament game, when Peter W. Gillgasch and Ernst A. Heinz founded IPD's computer chess group in mid-1993. Markus Gille joined the group in early 1994 and DARKTHOUGHT proceeded as a joint development of all three until Peter left the team in April 1996.
The central design philosophy of DARKTHOUGHT stresses a balanced combination of speed and knowledge that some other strong chess programs also seem to pursue. DARKTHOUGHT is neither heavily knowledge-based nor dumb and fast only - instead, it complements a speedy search with a fairly knowledgable evaluation. The successful tournament history of DARKTHOUGHT and its world-class test suite results for BT-2630 with a rating of 2494 ELO and LCT-II with a rating of 2535 ELO strongly support the validity of the combined approach.
Other important design principles of DARKTHOUGHT are configurability and portability. The program is written in ANSI-C and runs on various Unix platforms (e.g. DEC Alpha, HP PA-RISC, Intel x86, and Sun Sparc). Special source-code switches allow for the seamless selection of different implementations of time-critical functions. Thus, DARKTHOUGHT can easily be tailored for any desired platform (e.g. 32-bit versus 64-bit CPUs). Other switches create different search ``personalities'' without any loss of efficiency, thereby enabling frequent comparisons between the most interesting ones.
Today, DARKTHOUGHT is completely bitboard-based although it did not start as such. The elegance and performance potential of bitboards has lured researchers since the early days of computer chess. Several historically famous chess programs used bitboards while running on mainframes or vector supercomputers (e.g. KAISSA , CRAY BLITZ , CHESS 4.5 ). The advent of ever faster microprocessors with ever larger natural word lengths made the bitboard approach more and more attractive for microcomputer-based chess programs during the past years. Beside CRAFTY and DARKTHOUGHT there are now quite a few bitboard chess-programs around that have not yet emerged in public competition but will surely do so in the future. Furthermore, general interest in bitboards has increased significantly since Intel announced its next-generation 64-bit microprocessor to debut in 1998.
The remainder of this article firstly portrays a brief implementation history of DARKTHOUGHT in Section 1.2.3. Then it details the most important parts of the program: the bitboard engine in Section 1.2.4, the search engine in Section 1.2.5, and the evaluation engine in Section 1.2.6. Last but not least, the article concludes with an outlook on future work.