Author: Gerd Isenberg
Date: 14:02:04 09/12/03
Go up one level in this thread
On September 12, 2003 at 16:53:44, Omid David Tabibi wrote: >On September 12, 2003 at 16:49:09, Gerd Isenberg wrote: > >>On September 12, 2003 at 16:39:33, Omid David Tabibi wrote: >> >>>On September 12, 2003 at 16:34:48, Gian-Carlo Pascutto wrote: >>> >>>>On September 12, 2003 at 16:33:13, Omid David Tabibi wrote: >>>> >>>>>I still don't understand why modulus is needed, and >>>>>I have a pawn hash of 2^17 entries. What is so special >>>>>about pawn hash that you need the modulus operation >>>>>there while you don't need it in the normal hash table? >>>> >>>>You don't? >>>> >>>>I assume you have 32 or 64 bit hash keys. >>> >>>64 bit. >>> >>>> >>>>How do you map 2^64 -> 2^17 ? >>> >>>Please, don't tell me that you guys are mapping the hash key as following: >>> >>>address = key % table_size; >> >> >>Yes, unless you use zobrist keys and power of two table sizes for pawn hashing, >>which is probably smarter. Do you have a smarter way of getting a hashkey from >>white/black pawn bitboards? >> >>> >>>??? >>> >>>Do you know how many cycles does the modolus operation take??? >>> >> >>Yes, that's the reason for my initial posting. >> > >assuming 'table_size' is a power of 2, the following two expressions are >equivalent: > >address = key % table_size; >address = key & (table_size - 1); > Yes, but if "key" is whitePawns-blackPawns, bitboards as 64-bit ints, you may loose some pawns. That's the advantage with zobrist keys. I guess a 32-bit key, incremental updated if pawn structure changed, is good enough to address the pawn hash table. Gerd > > >>Gerd >> >>> >>>> >>>>-- >>>>GCP
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