Author: Frank Phillips
Date: 10:54:31 12/06/98
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On December 06, 1998 at 10:23:54, Robert Hyatt wrote: >On December 06, 1998 at 05:55:00, Frank Phillips wrote: > >>On December 05, 1998 at 21:36:46, Roberto Waldteufel wrote: >> >>> >>>On December 05, 1998 at 17:22:43, Frank Phillips wrote: >>> >>>>On a PII are programs based on bitboards inherently faster than those based on >>>>integer arrays? >>> >>>Hi Frank, >>> >>>On the Pentium, you have two very useful assembler instructions for bitboards, >>>the bsf and bsr instructions that find the first or last 1 bit in a 32-bit >>>number. These instructions are ideally suited to bitboard operations, but they >>>used to be terribly slow. Not any more, however: on the PII and PPro processors, >>>these instructions are very fast. As long as the testing is done on CPU >>>registers (not in memory), a bsf or bsr instruction executes in either 1 or 2 >>>CPU clocks (depending on pipelining efficiency). So on a PII or PPro I think >>>bitboards are a really big win, but if your program is going to be used on older >>>machines, you might think twice about using the bit scan instructions - they can >>>by more than 300 times slower in the worst case. >>> >>>Be careful how you code your bitboard routines if you try them. You will need to >>>code them in assembler, and it's quite fiddly to get right. But when you do, >>>bitboards fly on a PII. You might gain a good insight into bitboards by looking >>>at Earnst Heinz's Darkthought web site. If you are interested in implementing >>>rotated bitboards, Bob Hyatt is preparing (has prepared?) an article for ICCA >>>publication on the subject. He sent me a rough draft copy, and I found it >>>explains rotated bitboard implementation very well indeed. Whether or not >>>rotated bitboards are right for you depends on your program's data structures >>>and also on your implementation. My own experiments on a PII have shown that I >>>can generate the same information using ordinary bitboards faster than I can >>>using rotated bitboards, but the implementation I use relies very heavily on the >>>bit scan instructions, and as I said, these only became fast on the more recent >>>pentiums, and the rotated bitboards would undoubtedly be far superior on any >>>machine that did not offer this fast bit scan capability (eg pentium plain and >>>pentium MMX, also 486 has bit scans but they are slow) >>> >>>Hope this helps. Good luck! >>> >>>Roberto >>Roberto >> >>Thanks for the answer. I was wondering whether to make the leap to bitboards >>having just ?completed? the barebones of my first program based on the integer >>array approach in TSCP. I have no plans for the results of my rather mediocre >>efforts - just for personal interest. >> >>The problem as always is getting hold of information . >> >>Bob is your paper available other than by subscribing to ICCA? >> >>A while ago someone praised Bob Hyatt for all the help he gives to beginners and >>others alike. I whole heartedly endorse this and would also praise Tom Kerrigan >>for making TSCP readily available. As someone new to both programming and chess >>programming I found it a wonderful resource, without which I would probably >>never have got started. (Crafty is another well documented source, but way up >>the learning curve for a complete beginner). >> >>Frank > > >I haven't finished this yet... I've sent it to a couple of people in draft >form when they asked... And will do the same for you if you are interested. >Note that it is a rough draft, reasonably complete, but not "polished" yet... Bob Definitely interested.
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