Author: Robert Hyatt
Date: 06:03:43 12/10/99
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On December 10, 1999 at 00:50:44, Dann Corbit wrote: >On December 10, 1999 at 00:06:05, blass uri wrote: > >>I am interested in this question because I understood that >>64 bit signature may be counter productive at correspondence time control >>and I would like programs to avoid mistakes even in 24 hours/move. >> >>How much slower are program if you use 96 or 128 bit signature instead of 64 bit >>signature? >The problem I see for a big signature is that you will get a smaller number of >entries. >Let's imagine some extremes. Your hash signature is 1K. You have 4K space for >hash entries. That means you have 4 evals you get to store. ;-) >Now, if you double your hash signature to 2k, you only store 2. If you double >it again you only store 1. > >So there is a trade off. If you increase the size of your hash it will reduce >the number of table entries you can store. If you decrease the size of your >hash, it will increase the false matches and increase the probability of error. > >So do you want to spend a ton of time flushing old cash entries or do you want a >lot of bad hits? > >The solution for bigger hash signature is to get a bigger memory. If you have >512 megs, then you could store a large number of big hash signatures. > >So if you want to do correspondence chess, get a zobrist hash that does >somewhere from 64 to 128 bits on its output. Then, make a hash table with >16,000,000 entries at 128 bits or 32 million at 64 bits and it will consume 256 >megs of ram. > >So it seems (to me) to be a balancing act. I don't see the connection between hash signature and table size. I use a 64 bit signature, which means I can use _any_ table size up to 2^64... I can even go beyond 2^64 entries by using what is commonly called 'buckets'. (A bucket is a set of entries rather than a single entry. Then I would probe to a specific bucket. I would need some way to differentiate between the different positions that produce the same hash signature for that bucket of course, if I use 2^64 buckets or more..)
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