Author: Christophe Theron
Date: 11:19:42 04/10/04
Go up one level in this thread
On April 10, 2004 at 12:46:23, Anthony Cozzie wrote:
>On April 09, 2004 at 23:48:36, Christophe Theron wrote:
>
>>On April 09, 2004 at 16:51:34, Anthony Cozzie wrote:
>>
>>>On April 09, 2004 at 15:26:34, Christophe Theron wrote:
>>>
>>>>On April 09, 2004 at 14:27:48, Sune Fischer wrote:
>>>>
>>>>>
>>>>>>Clearly, nothing beats the ugliness of bitboards.
>>>>>
>>>>>This may not be the best example to judge by.
>>>>>
>>>>>-S.
>>>>>> Christophe
>>>>
>>>>
>>>>
>>>>In the contrary, I think it's fairly typical of bitboard code.
>>>>
>>>>Elegance is supposed to be the strong point of bitboards.
>>>>
>>>>The only thing I find elegant is the pseudo-great starting idea "64 squares <->
>>>>64 bits".
>>>>
>>>>Passed this point everything becomes unreadable and ugly.
>>>>
>>>>I also see it often used to pre-compute attack tables and such, which is in my
>>>>opinion contrary to one of the most important things I have learned in computer
>>>>chess: do not compute anything in advance if you are not certain that you will
>>>>use it. This is not an intrinsic problem of bitboards, it's just that use of
>>>>bitboards often go along with this misuse of computing resources, is it just by
>>>>chance?
>>>>
>>>>Bitboards are a great tool allowing you to compute very complex things in a
>>>>blink. The problem is that in a chess program you rarely need to do these
>>>>complex computations if you know what you are doing, and so you end up with ugly
>>>>and unreadable code and waste of resources (in particular of L1 and L2 caches).
>>>>
>>>>That being said, I do not want to be too harsh: it is probably possible to write
>>>>a top-level chess program using bitboards, a program that would be not very far
>>>>behind the programs using more portable approaches like 0x88 and derivatives.
>>>>
>>>>Somebody will write one some day.
>>>>
>>>>
>>>>
>>>> Christophe (setting up a shield for the upcoming flame)
>>>
>>>Correct me if I am wrong, but aren't attack tables the exact opposite of your
>>>"do not compute anything in advance" strategy?
>>>
>>>anthony
>>
>>
>>
>>Absolutely, and I think that computing attack tables at every node is
>>inefficient, and I do not do it. Some say bitboards can do that quickly, but I
>>have not use for it.
>>
>>Not sure if you have read my post correctly (or maybe I did a mistake?).
>>
>>
>>
>> Christophe
>
>
>Ah, I thought tiger used attack tables. I seem to remember some post by you
>where you claimed "Tiger is optimized for determining whether a piece attacks a
>square" or some such.
>
>anthony
I don't know to what message you are referring to, but:
* it would not imply that I use attack tables
* most chess programs are optimized to do that efficiently anyway
I don't use attack tables or updating attack tables. When I need to know if X
attacks Y, I have to compute it because I have not stored this information
anywhere. It may happen that for a given node I compute the same attack info
twice (it does not happen often, fortunately).
Only exception is check. My makemove always look for a check and I have an
"incheck" flag for each side (for the side not to move it can be considered as
an "illegal position" flag).
Christophe
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