Author: Sune Fischer
Date: 05:57:55 12/01/03
Go up one level in this thread
On December 01, 2003 at 08:19:50, Tord Romstad wrote:
>On December 01, 2003 at 07:33:51, Tom Likens wrote:
>
>>I'm toying with adding full attack tables to my engine. Do you incrementally
>>update your attack tables or do you generate them from scratch?
>
>It's funny that you ask this question right now, because I posted my new
>attack table generation code just a couple of hours ago. :-) I don't want
>to show you the old code, partly because it is too embarassing to show,
>and partly because it is so mind-bogglingly ugly that the memory of having
>seen it would probably give you nightmares for the rest of your life.
>
>I have always generated the attack tables from scratch at every node. The
>complexity of updating them incrementally scares me, and those who have tried
>usually claim that it is slower than generating them from scratch anyway.
That will probably depend on the design of the table.
I stored attack to and attack from information which can be used to do
incremental updates.
When moving a piece you take all the sliding pieces attacking the affected
squares (that's just a few masks with bitboards) and invalidate their attack
boards along with the moving piece and the one it might have captured.
Now you have a list of pieces who's attack boards may be invalid.
You run through this list and generate their new attack boards, you xor the new
attack board with their old attack board (which is stored in the attack table)
to get the squares which changed attack status, these you update.
Hope that made sense :)
I posted the code once, here is the main loop
inline void BOARD::GenAttackers(uint32 affected,uint co) {
register BITBOARD xors;
register uint ix;
while (affected) {
ix = FirstBit32(affected);
xors = attack_ix[ix];
attack_ix[ix] = GenAttack(ty_ix[ix],sq_ix[ix],co);
xors ^= attack_ix[ix];
while (xors)
attack_sq[GetFirstBitAndClear64(xors)] ^=(1<<ix);
affected &= affected-1;
}
}
affected is a 32 bit piece list
attack_ix stores the attack board of piece with index ix
attack_sq stores attackers to sq
-S.
>Tord
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