Author: martin fierz
Date: 15:01:44 02/11/04
Go up one level in this thread
On February 11, 2004 at 17:25:06, Dann Corbit wrote:
>On February 11, 2004 at 17:11:57, Dann Corbit wrote:
>
>>On February 11, 2004 at 16:43:06, martin fierz wrote:
>>
>>>on my long todo list for my program, the item "pawn hashing" has slowly but
>>>steadily floated upwards. now it's on top. so: how large is your pawn hashtable
>>>(in # of entries)? how large are your entries? i'm using bitboards, and it seems
>>>to me that my entries will be huge, e.g. if i want to save some simple stuff
>>>like
>>>
>>>- passers
>>>- connected passers
>>>- isolated pawns
>>>- doubled pawns
>>>- backward pawns
>>>- blocked pawns
>>>
>>>that would be 6x8 = 48 bytes; perhaps times 2 for each side (or i could pop
>>>black and white pawns in the same bitboard, and & it with the black/white
>>>bitboard to save space). still, that's already 48 bytes and i guess i could save
>>>some more stuff if i thought about it a bit longer :-)
>>>is that a reasonable size for a pawn hash entry?
>>
>>The pawn hash table only holds a hash of [the pawn positions, colors, e.p. flag
>>and (usually) the king position.] So one 64 bit number gets stored as the
>>position in the array and the key {of 64 - address bits.}
>>
>>The key is used to know that your hash does not collide.
>>You also store the overall pawn score (most people use a signed short between
>>+32766 and -32767). You add up all of the terms above into a single value for
>>this score.
>
>Suppose that you have a board position like this:
>[D]2r1kq2/2r5/7p/1pPp2pP/pP1PppP1/P3P3/2Q2N2/1B2K3 w - -
>
>Your pawn hash deals only with this:
>[D]4k3/8/7p/1pPp2pP/pP1PppP1/P3P3/8/4K3 w - -
>
>The hash will be some number like 1909174647730783536 which is 1A7EC03A142CC530
>in hex.
>
>Suppose (for instance) that you have 65536 entries in your hash table (16 bits
>in length)
>Then you would use the first 16 bits (actually it does not matter which bits you
>choose as long as your hash is fairly random) of the hash for your address into
>the hash table.
>1A7E = 6782 is the address in the hash table.
>
>Then the remaining 48 bits becomes a key, so you know for sure that ther is no
>collision. (Some forgo this step, but I like to keep it. Memory is cheap).
>
>key = C03A142CC530 = 211355679114544
>
>And then you store also a score like -15 centipawns.
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.
cheers
martin
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