Author: Robert Hyatt
Date: 07:23:54 12/06/98
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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...
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