Author: Dan Newman
Date: 17:53:55 09/21/98
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On September 21, 1998 at 18:56:46, John Coffey wrote: >On September 21, 1998 at 18:12:36, Tom Kerrigan wrote: > >>Mostly correct, although maintaining two numbers to describe the position is >>overkill. One 64 bit number should be enough. >> > >Is one 64 bit number enough to uniquely identify a position? Does this >prevent two positions from getting the same hash key? > >I assume that you convert your hash key into an index into the history. >I assume that you take your 64 bit number and divide it by a constant >(or right shift it) to get the number of entries available in your hash >table? i.e. 64 megs would be 4 million positions. > >John Coffey There are many orders of magnitude more positions than 2^64 of course, so every hash code corresponds to a stupendously large number of positions. But, with 64 bits you get a hashing error only rarely (or at least it should be rare, and you hope that that occasional error doesn't lose a game). I mask off a certain number of bits to form the index into the hash table (20 or so), the rest of the bits I store in the table entry to test against. -Dan.
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