Computer Chess Club Archives




Subject: Random keys and hamming distance

Author: James Swafford

Date: 20:26:08 08/16/02

I'm in the process of tracking down some hashing problems, and
I'm starting with my Zobrist keys.  For each piece (i.e. bp, wp,
wr, ...) I have 64 keys.  I have 65 keys for "ep square", two
for "player to move", 16 for castling rights.  All keys are 64 bits.

I just did a test to find the minimum hamming distance among
all keys, and it was 14 bits.  That seems a bit low.

I think the way I'm doing 64 bit random number generation sucks.
Here it is:

Bitmap RandomBitmap(void)
   Bitmap r1,r2;


   return ((r1<<32)|r2);

Ok, someone please confirm that this sucks and tell me a better
way. :)

I'm also interested in hearing what others are getting for min
hamming distance between keys.


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