Author: Omid David Tabibi
Date: 14:06:15 09/12/03
Go up one level in this thread
On September 12, 2003 at 17:02:04, Gerd Isenberg wrote: >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. > Well, well... In this case I must quote Vincent: don't waste time with bitboards :) But seriously, I have always used zobrist keys for pawn hash tables. Incrementally updating the pawn key, the cost is negligible. >Gerd > > >> >> >>>Gerd >>> >>>> >>>>> >>>>>-- >>>>>GCP
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.