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Don Dailey

Joined: 29 Apr 2008
Posts: 4502

Post subject: Re: Zobrist alternative?    Posted: Fri Jun 15, 2012 10:59 pm

Daniel Shawul wrote:
 Quote: The same number? Maybe that is why it's called a constant? I don't understand your point, but this is the famous Fowler/Noll/Vo hash which has been found to work very well. Essentially we are applying the FNV hash to the tuple (color, type, square.) There are actually two constants, the first is called the offset basis and is claimed to not be important, just to provide a consistent way to start this off. FNV is called the FNV prime. It is a magic constant that has certain properties that are considered important for this particular hash.

No I clearly understand what you are trying to do. There is the cp (color/piece) and (square) indexes. You had FNV hash xored first then multiplied with FNV but this is not how FNV hash works. It should be reversed which I thought was a typo. But I am not sure anymore since you say now it should be xor first. Anyway you are using the FNV hash twice to get a single key. The fact that the two steps are mixed make it a bit different but basically it will suffer from the problems I mentioned.

The issue with the 2 constants would be optimized away by any compiler and it was just a sloppy translation on my part. There are however 2 constants but one is just used for initialization and is not particularly important.

There are at least two versions of this hash and the one considered superior does the xor first, that is called (I think) FNV-1a if I remember correctly and the one that should be used for this.

Here is my suggested usage:

h = 19282138887198ull;
h = h ^ color_piece;
h = h * FNV_CONSTANT;
h = h ^ square_number;
h = h * FNV_CONSTANT;

This will come out differently for every piece on every square. The only way this varies from proper FNV-1a is that normally you look at 8 bits of key at a time - that is what is xor'd - so to do this the proper FNV way HG might wish to do an extra xor and multiply (if his key is as much as 24 bits.) But I believe this would work just fine.

There is a chance it wouldn't so it would need to be checked out but the hash itself is consider to be reasonable sound for general hashing.
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H.G.Muller Tue Jun 12, 2012 7:35 pm
Kevin Hearn Tue Jun 12, 2012 7:44 pm
Daniel Shawul Tue Jun 12, 2012 8:19 pm
H.G.Muller Tue Jun 12, 2012 8:54 pm
Daniel Shawul Tue Jun 12, 2012 9:46 pm
Daniel Shawul Wed Jun 13, 2012 3:24 am
Daniel Shawul Wed Jun 13, 2012 4:14 am
Daniel Shawul Wed Jun 13, 2012 4:00 pm
Daniel Shawul Thu Jun 14, 2012 1:30 am
H.G.Muller Thu Jun 14, 2012 5:50 am
Daniel Shawul Thu Jun 14, 2012 12:52 pm
Edmund Moshammer Thu Jun 14, 2012 8:21 am
Edmund Moshammer Thu Jun 14, 2012 9:27 am
Wylie Garvin Tue Jun 12, 2012 8:27 pm
H.G.Muller Tue Jun 12, 2012 8:36 pm
Vincent Diepeveen Wed Jun 13, 2012 1:01 pm
Wylie Garvin Wed Jun 13, 2012 10:57 pm
H.G.Muller Thu Jun 14, 2012 5:42 am
Robert Hyatt Thu Jun 14, 2012 1:17 pm
H.G.Muller Thu Jun 14, 2012 2:17 pm
Wylie Garvin Thu Jun 14, 2012 6:11 pm
Vincent Diepeveen Sat Jun 16, 2012 10:05 am
Reinhard Scharnagl Wed Jun 13, 2012 9:52 am
Edmund Moshammer Wed Jun 13, 2012 9:58 am
Reinhard Scharnagl Wed Jun 13, 2012 12:49 pm
Edmund Moshammer Wed Jun 13, 2012 1:15 pm
Reinhard Scharnagl Wed Jun 13, 2012 1:41 pm
Edmund Moshammer Wed Jun 13, 2012 3:55 pm
Reinhard Scharnagl Wed Jun 13, 2012 4:03 pm
H.G.Muller Wed Jun 13, 2012 2:19 pm
Vincent Diepeveen Wed Jun 13, 2012 2:44 pm
Vincent Diepeveen Wed Jun 13, 2012 2:48 pm
Vincent Diepeveen Wed Jun 13, 2012 3:28 pm
H.G.Muller Wed Jun 13, 2012 4:01 pm
Vincent Diepeveen Wed Jun 13, 2012 5:42 pm
H.G.Muller Wed Jun 13, 2012 5:51 pm
Vincent Diepeveen Wed Jun 13, 2012 6:27 pm
Daniel Shawul Wed Jun 13, 2012 5:29 pm
Karlo Bala Jr. Thu Jun 14, 2012 9:50 am
Reinhard Scharnagl Thu Jun 14, 2012 8:49 am
H.G.Muller Thu Jun 14, 2012 9:09 am
Daniel Shawul Thu Jun 14, 2012 1:11 pm
Vincent Diepeveen Sat Jun 16, 2012 10:12 am
Don Dailey Thu Jun 14, 2012 4:46 pm
Don Dailey Thu Jun 14, 2012 6:38 pm
Daniel Shawul Thu Jun 14, 2012 6:57 pm
Don Dailey Fri Jun 15, 2012 2:39 pm
H.G.Muller Fri Jun 15, 2012 3:46 pm
Daniel Shawul Fri Jun 15, 2012 5:22 pm
H.G.Muller Fri Jun 15, 2012 5:38 pm
Vincent Diepeveen Sat Jun 16, 2012 10:17 am
Daniel Shawul Fri Jun 15, 2012 5:04 pm
Don Dailey Fri Jun 15, 2012 6:00 pm
Daniel Shawul Fri Jun 15, 2012 7:27 pm
Don Dailey Fri Jun 15, 2012 8:16 pm
Daniel Shawul Fri Jun 15, 2012 8:42 pm
Daniel Shawul Fri Jun 15, 2012 9:14 pm
Re: Zobrist alternative? Don Dailey Fri Jun 15, 2012 10:59 pm
Daniel Shawul Sat Jun 16, 2012 12:17 am
Don Dailey Sat Jun 16, 2012 4:28 am
Daniel Shawul Sat Jun 16, 2012 6:30 am
Daniel Shawul Sat Jun 16, 2012 10:09 am
Vincent Diepeveen Sat Jun 16, 2012 10:22 am
Vincent Diepeveen Sat Jun 16, 2012 10:42 am
Vincent Diepeveen Sat Jun 16, 2012 10:54 am
Daniel Shawul Sat Jun 16, 2012 11:03 am
Vincent Diepeveen Sat Jun 16, 2012 11:08 am
Don Dailey Sat Jun 16, 2012 12:03 pm
Vincent Diepeveen Sat Jun 16, 2012 12:55 pm
Vincent Diepeveen Sat Jun 16, 2012 2:21 pm
Daniel Shawul Sat Jun 16, 2012 2:25 pm
Vincent Diepeveen Sat Jun 16, 2012 2:44 pm
Daniel Shawul Sat Jun 16, 2012 12:35 pm
Vincent Diepeveen Sat Jun 16, 2012 1:11 pm
Vincent Diepeveen Sat Jun 16, 2012 1:15 pm
Vincent Diepeveen Sat Jun 16, 2012 1:56 pm
Daniel Shawul Sat Jun 16, 2012 2:05 pm
Vincent Diepeveen Sat Jun 16, 2012 2:10 pm
Daniel Shawul Sat Jun 16, 2012 2:22 pm
Vincent Diepeveen Sat Jun 16, 2012 2:29 pm
Daniel Shawul Sat Jun 16, 2012 2:35 pm
Vincent Diepeveen Sat Jun 16, 2012 2:39 pm
Don Dailey Sat Jun 16, 2012 3:49 pm
Daniel Shawul Sat Jun 16, 2012 4:35 pm
Daniel Shawul Sat Jun 16, 2012 2:11 pm
Vincent Diepeveen Sat Jun 16, 2012 2:13 pm
Vincent Diepeveen Sat Jun 16, 2012 2:19 pm
Daniel Shawul Sat Jun 16, 2012 2:29 pm
Vincent Diepeveen Sat Jun 16, 2012 2:32 pm
Daniel Shawul Sat Jun 16, 2012 4:19 pm
Don Dailey Sat Jun 16, 2012 4:50 pm
Daniel Shawul Sat Jun 16, 2012 4:25 pm
Don Dailey Fri Jun 15, 2012 8:21 pm

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