Author: Christophe Theron
Date: 11:15:55 06/21/00
Go up one level in this thread
On June 20, 2000 at 21:22:38, Ricardo Gibert wrote:
>On June 20, 2000 at 21:09:58, Christophe Theron wrote:
>
>>On June 20, 2000 at 14:58:54, James Robertson wrote:
>>
>>>On June 20, 2000 at 12:18:06, Ralf Elvsén wrote:
>>>
>>>>I'm asking about things I don't have much personal experience from
>>>>so forgive me if this is a stupid question. With BB, as I understand
>>>>it, one usually have a lot of precomputed BB-arrays, like bishopsMoves[square],
>>>>maybe blocks[from][to] or the rotated BB-stuff. Is this causing problems
>>>>for the cache? How much precomputed stuff is needed in 0x88 compared to this?
>>>>
>>>>Ralf
>>>
>>>I'll answer your second question first. A tiny amount (guesstimate, maybe 1k) is
>>>needed for 0x88. Bitboards require much more... almost 600k for core arrays on
>>>my program. Crafty uses some funky thing called compact attacks which I guess
>>>compacts the attacks. I don't know how it works. (Dr. Hyatt, could you please
>>>explain how it works and what it's advantages are?)
>>>
>>>The precomputed arrays are usually in the form of attacks for ranks and files.
>>>To try to stuff all bishop or rook moves into one array is a bad idea. For
>>>instance, in my program, rook moves would require an array of dimensions
>>>8*64*256*256 bytes = 33MB!
>>>
>>>Taking two arrays, one for ranks and one files (each 8*64*256 = 131072 bytes) is
>>>a lot better.
>>>
>>>James
>>
>>
>>I thought bitboards were elegant?
>>
>>Sorry, but 128K arrays to do such simple things sounds really ugly!
>>
>>Like a hammer to kill a fly.
>
>I'm not sure I understand your analogy. It would seem to me to be much more
>difficult to kill a fly with a hammer, than with a much more appropriate tool
>like a fly swatter.
>
>I think your analogy would work better with a shotgun, though given the
>irritation factor of some flys, a shotgun does not seem like such a bad idea ;)
A shotgun, if you want. Anyway, for me that's the same.
Tell me about the elegance of the bitboard concept, after that...
A 0x88 or 16x engine: 64Kb
A bitboard engine: 2MB
They are of equal strength.
But the bitboard design is so smart! And when we have 64 bits processors, the
bitboard program will not be stronger, but it will fit the processor's
architecture so nicely! Just thinking about it makes me wet everywhere!
Cute piece of expensive art I would say.
Christophe
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