Author: James Robertson
Date: 16:03:34 06/19/00
Abstract: For the last several days, I have been frantically trying to prove that my beloved rotated bitboards I spent two years on are as fast as the 0x88 code I threw together in about an hour. Conclusion: life is not fair. Materials & Methods: I managed to speed up my bitboard move generation by 50% and bring it almost to the speed 0x88 move generation provides. In most positions my rotated bitboards are less than 10-20% slower than the 0x88 code. I could live with that, as potential speedups in well written code elsewhere and the hope of 64-bit processors that all us bitboard guys look forward to would be sufficient compensation. However, the story seems to get worse. Not surprisingly, making/unmaking moves is hopelessly slower than in 0x88 (only divine replanning of the universe will change that), but even functions such as check detection become slower than 0x88 as the pieces come off. Rotated bitboards do have several saving graces, not the least of which is capture generation. For instance, in the position 4k3/8/8/8/8/8/8/RNBQKBNR - - rotated bitboards are almost 500% faster! Even in less extreme positions, they still hold a healthy edge. Certain aspects of a scoring function are also greatly increased in speed. Mobility scoring can be much faster, but when it reaches the complexity of what I am writing for Insomniac 0x88 may catch up or even surpass the capability of rotated bitboards. My actual conclusions are... I don't really know. I will have to rewrite Insomniac from the ground up, as the new and improved bitboard code I wrote for the "speed race" will be almost impossible to move into the old version. So.... I have a choice now between 0x88 and rotated bitboards, and am hoping maybe some of you could give me advice. Is there anyone else who has worked extensively with both systems? Anyone who has done more quantitative comparisons? On the side of 0x88 seems to be speed and simple code, but I am emotionally attached to rotated bitboards and the hope of increased speed on 64-bit processors is tantalizing. Thanks for any help. James
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