Author: Alessandro Damiani
Date: 14:41:11 06/14/00
Go up one level in this thread
On June 14, 2000 at 16:17:25, Christophe Theron wrote: >On June 14, 2000 at 15:01:32, Dann Corbit wrote: > >>On June 14, 2000 at 06:56:27, Christophe Theron wrote: >>>On June 14, 2000 at 05:32:16, Alessandro Damiani wrote: >>>>On June 13, 2000 at 23:18:54, Christophe Theron wrote: >>>>>On June 13, 2000 at 16:53:39, Eugene Nalimov wrote: >>>>>>Combine two approaches -- 0x88 and 10x12. Use 12x16 board, and access board by >>>>>> board[0x20+square] >>>>>>(In C/C++ you can define macro for that). >>>>>> >>>>>>Than in each case you can use more appropriate of 2 methods. >>>>> >>>>> >>>>>Well actually Eugene it is what I do already. Sorry, I should have stated this >>>>>more clearly in my post. I don't use 12x12 or 10x12. I use 16x16 (actually I >>>>>just need 16x12). >>>>> >>>>>I don't even need to add 0x20... That's why I think 16x12 is more efficient than >>>>>0x88, and this comes from close examination of what a typical chess program does >>>>>most of the time. >>>>> >>>>> >>>>> Christophe >>>> >>>>The next step are bitboards. >>>> >>>>Alessandro >>> >>> >>>How many of the top programs actually use bitboards? >> >>My guess is that of those programs which are for sale, none of them do. >>The reason I guess this, is that the programs have been under development for a >>long time. They probably started out with one of the representations before >>bitboards. To change over to bitboards would require some tangible benefit. >>Since for 32 bit processors, the change is negligible, I strongly suspect that >>none of the professional programs have done this. >> >>However, once the 64 bit processors become mainstream, I expect all of them to >>make the transition at some point. > > >Don't be so sure. For example in my program I see no part that could be improved >with bitboards. I just don't need them. > >I really think that bitboards have no intrinsic objective advantage. That's just >another way of representing things. > >It is elegant and COULD be used to simplify complex operations, but the key >point is that in a chess program these complex operations are simply not >required... > >You can give me whatever example of an operation elegantly handled with >bitboards, but if your example is realistic and is really used in a chess >program I'm sure I can do the same thing with my data representation with no >additional cost. > >I have heard examples of ways of evaluating passed pawns that were alledgedly >faster with bitboards, but I do these evaluations in my program without >bitboards, and without pain... > >If you manage to find an occurence where bitboards are really useful and faster, >I'm pretty sure it will represent less than 1% of CPU usage in a real chess >program. > >It ends up being noise, because a 1% speedup, or even 10%, can be achieved by >other ways. For example optimizing for the cache architecture of your target >processor. The intrinsic speed provided by the basic data design (bitboards or >not) becomes hidden by other very platform specific designs. > >The availability of 64 bits processors changes nothing. Unless some 64 bits >processors are so lousy that 8, 16 and 32 bits operations become slower than 64 >bits ops...! :) > >I don't mean this to be a critic of the bitboard design. Bitboards are really >very elegant, and certainly very interesting to program. But I see no objective >reason to chose them because they are more effective. They are not. They are >approximately as effective as 0x88 or other arrays based designs. > > > Christophe I do detection (not evaluation) of passed pawns incrementally. A few ANDs and all passed pawns are in one bitboard. Since I evaluate all pawns without scanning them (evaluation is also depending on attack information!), it is faster than scanning all pawns and check if they are passed. Alessandro
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