Author: Uri Blass
Date: 02:35:09 02/12/04
Go up one level in this thread
On February 12, 2004 at 04:59:29, martin fierz wrote:
>On February 11, 2004 at 18:37:48, Dann Corbit wrote:
>
>>On February 11, 2004 at 18:29:53, martin fierz wrote:
>>
>>>On February 11, 2004 at 18:13:25, Dann Corbit wrote:
>>>
>>>>On February 11, 2004 at 18:01:44, martin fierz wrote:
>>>>[snip]
>>>>>hi dann,
>>>>>
>>>>>i am quite aware that a normal hashtable works as you say - store a key and a
>>>>>score. but really, i think that is a much too simplistic view of pawn structure.
>>>>>pawns interact with pieces in complex ways, and i basically would like to store
>>>>>the information i think important about pawns in the pawn hashtable, to retrieve
>>>>>them quickly later. i can also imagine storing a "baseline score" for the given
>>>>>pawn configuration. but i really want interactions with pieces too, and as i
>>>>>can't hash scores for that, i'd have to save intermediate computations (such as
>>>>>connected passers, or potential levers etc) in the pawn hashtable, and then use
>>>>>them for the interaction terms.
>>>>
>>>>I bet it will be more expensive to store all that stuff in the hash table and
>>>>try to reuse it than to recalulate it.
>>>
>>>one hashlookup will cost something like the average memory latency for
>>>non-cached stuff. that's probably around 50-100 processor cycles. if there are
>>>more than 100 processor cycles in what i store, i should be fine.
>>>
>>>>The best thing about the pawn hash table is that the kings and the pawns move
>>>>slowly. You don't see a ton of rapid change and so a small table gives a lot of
>>>>hits. If you want to store things about rooks backing pawns and other things of
>>>>that nature, I think the table will change quickly. What will you have? An
>>>>ordinary hash table entry. So why bother with it?
>>>
>>>nope, that's not the idea. i want to store pawn stuff only, of course. but
>>>instead of keeping a score, i would store, for example, a passed pawn bitboard;
>>>or a bitboard with all bits set behind passed pawns. then a simple & with the
>>>rook bitboard gives me supported passed pawns. you can imagine more complex
>>>stuff to do, like you could look at the pawn structure and produce a bitboard of
>>>squares where you think your king is safe and where not. then again, a simple &
>>>gives you the answer.
>>
>>I guess what I am saying is that the benefit of a pawn hash will be lost if you
>>do too much work. After all, all of the above calculations will be stored in
>>the regular hash. So you will not redo them if you have seen the position
>>before. And if something changes, you will have to recalculate.
>
>no, you are completely misunderstanding the idea. i want to store *intermediate*
>calculations in my pawn hash, which are not scores at all, but simply
>pawn-related stuff that i can use all over my evaluation. instead of computing
>all that pawn-related stuff at every node. since these are only related to
>pawns, i don't have to recalculate anything if the pawn structure doesn't
>change. as an example, take the task of finding isolated pawns in a bitboard. i
>don't know how to do this efficiently. my code to do this is extremely ugly and
>slow.
Here is my code for it(this is the code that Gerd posted so it is not exactly my
code)
BitBoard FillDownBoard(BitBoard bb)
{
bb|=(bb>>8);
bb|=(bb>>16);
bb|=(bb>>32);
return bb;
}
BitBoard FillUpBoard(BitBoard bb)
{
bb|=(bb<<8);
bb|=(bb<<16);
bb|=(bb<<32);
return bb;
}
pawnattacksAH[LIGHT]=(pawnBB[LIGHT]<<9)&NOTFILEABB;
pawnattacksHA[LIGHT]=(pawnBB[LIGHT]<<7)&NOTFILEHBB;
pawnattacks[LIGHT]=(pawnattacksAH[LIGHT]|pawnattacksHA[LIGHT]);
isolatedpawns[LIGHT]=(pawnBB[LIGHT]&~FillDownBoard(FillUpBoard(pawnattacks[LIGHT])));
pawnattacksAH[DARK]=(pawnBB[DARK]>>7)&NOTFILEABB;
pawnattacksHA[DARK]=(pawnBB[DARK]>>9)&NOTFILEHBB;
pawnattacks[DARK]=(pawnattacksAH[DARK]|pawnattacksHA[DARK]);
isolatedpawns[DARK]=(pawnBB[DARK]&~FillDownBoard(FillUpBoard(pawnattacks[DARK])));
Note that I do this code only when it is needed(only after pawn moves or
captures of pawns that may change the isolated pawn information so I have if
code to implement this code only when I make move or unmake move that may change
the information).
Uri
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