Author: Carlos del Cacho
Date: 09:31:07 09/14/00
Go up one level in this thread
On September 14, 2000 at 09:58:35, Andreas Herrmann wrote:
>On September 14, 2000 at 08:38:31, Andrew Williams wrote:
>
>>On September 14, 2000 at 05:25:32, Andreas Herrmann wrote:
>>
>>>On September 13, 2000 at 17:12:07, Andreas Herrmann wrote:
>>>
>>>>Hello,
>>>>
>>>>i want to include pawn hash tables in my chess program holmes, but i don't know
>>>>how i have to calculate the hash index and the hash key.
>>>>I think the hash index of the position will only calculated with the pawns on
>>>>the board like the following,
>>>>
>>>>for (pos=A1;pos<=h8;pos=pos+1) {
>>>> if (figure[pos]=pawn) {
>>>> PawnHashIndex = PawnHashIndex ^ RandomIndex[pos].index;
>>>> }
>>>>}
>>>>
>>>>is this right??
>>>>
>>>>How can i get a good hash key? What have i calculate with xor?
>>>>
>>>>Thanks for each information.
>>>>
>>>>Andreas
>>>>
>>>>
>>>>www.wbholmes.de
>>>
>>>Hello again,
>>>
>>>the links from Ricardo are a good information source, but i found nothing about
>>>pawn hash tables, only normal hash table and that's not new for me.
>>>
>>>My question is how can i get a good hash key for collision check in the pawn
>>>hash table.
>>>Is a XOR combination with a random figure enough? Or is it not so difficult than
>>>i am thinking?
>>>
>>>Andreas
>>
>>Yes. I've always used a 64-bit integer derived in just the way you describe.
>>I don't know if 32-bits would be sufficient, as I've never tried it.
>>
>>Andrew
>
>Ok a 64-bit integer is of course much better against hash collision than a
>32-bit. I will try to implement it with a 64-bit interger.
>
>thanks
>Andreas
I've been using 32 bit nums since I first implemented it in pepito a few months
ago, and I haven't had any problem with collisions yet. I guess the pawn
structure changes so slowly in search that the chances of getting a collision
are really small unless you get to incredibly deep lines (with lots of pawn
moves... I don't think that's possible).
Carlos
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