Author: Scott Gasch
Date: 19:51:41 08/05/99
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Both Bob and Bruce mentioned a small hash table specifically for detecting repetition. I guess this would be implemented as an array of counts indexed by a subset of the position's hash key -- say the last n bits. What is to prevent false draw reading, however, if two (different) positions in the same search yield the same key subset (and artificially inflate the count). Related question: I am initializing my transposition hash square-piece array with just random numbers (rand()). This is not good for many reasons: 1) if the random numbers I get (seeded off system clock) are bad (not very random) hashing performs badly and we have many collisions (I have not really seen this happen but in theory I guess it could). 2) there is no way I can predict what a key for a given position will be beforehand which is okay now but when I write an opening book I'd like to be able to do this. So definately I need some kind of function to generate the seeds. My (next) question is this -- what do you guys do for said function? I am computing two numbers for each position - a key and a checksum. The key is just xors of seeds for piece/square and the checksum is adding and subtracting seeds. I had considered using prime numbers for the seeds but I don't see how that really will help produce a uniform hash distribution. Scott
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