Author: Robert Hyatt
Date: 13:31:56 11/02/98
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On November 02, 1998 at 10:13:52, Ernst A. Heinz wrote: >On November 02, 1998 at 08:32:48, Robert Hyatt wrote: >> >> [...] >> >>how many entries? IE I never paid attention to this hash number when we ran >>on a 16gb machine because we used such rediculously large hash tables. But if >>you can get such a large hit percentage with pawns+kings, then the original >idea >>of pawns+kings+rooks ought to be pretty close, because even the king can walk >>a long way in a 12 ply search... >> >>however I generally run with 10mb pawn hash, which is something like 500K >>entries, and don't ever see this number under 99% (integer truncation)... I'd >>think it has to be bigger to stick at 99% with kings factored in...??? > >No, at least not according to my tests. In "DarkThought" it works just fine >starting with 512K entries and does not decrease badly if you scale the numbers >of entries back to 128K. Please note that we do not factor in both Kings at >once but rather distinguish between Black and White. Still, we only keep a >single hash table for our complete King+Pawn hashing because of performance >considerations (albeit with different keys and locks for Black and White). I >think that lazy evaluation and capture-only quiescence enable us to factor the >King in without much degradation of the hit rate (we hardly ever evaluate any >non-quiescence nodes). Of course, it is also crucial to factor the Kings out >as soon as they start to wander far around the board. > >Unfortunately, the addition of any other piece to the hashing drops the hit >rate to 50%--75% just as the original poster reported. I have not yet found >the cute trick that let's me raise this rate ... :-( > >=Ernst= It would still seem that this should be worse... because you have the same pawn structure hashed multiple times with different king positions, and now you have the same pawn structure hashed once with each side's king position, which seems like you hash each pawn structure *twice*??? I'm not sure I follow? Two separate hash keys dynamically updated? Pawn hash with king hash folded in at probe time? Two stores, once for each king position, but with the same pawn structure stuff??? Bob
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