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Subject: Re: 0x88 is not so smart

Author: Peter McKenzie

Date: 15:42:33 06/14/00

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On June 14, 2000 at 17:41:11, Alessandro Damiani wrote:

>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.

You don't need a bitboard program to do this.  You can just store the passed
pawn information (in bitboard form or some other form) in the pawn hash table.

>
>Alessandro



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