Author: David Rasmussen
Date: 00:20:36 12/05/01
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On December 04, 2001 at 20:11:34, martin fierz wrote: >On December 04, 2001 at 09:16:22, Severi Salminen wrote: > >>Hi! >> >>What is the definition of "hamming distance"? What characteristics should I test >>when testing my random numbers' suitability for zobrist keys? What alternatives >>there are for random number generators besides the rand() in C? >> >>Severi > >aloha! > >my experience is from a checkers program, but it shouldnt really matter. >i am using 32-bit random numbers generated by calling rand() twice, because >rand() only returns a 16-bit value on my compiler. i used to use these numbers >and read some posts here about hamming distance, so i decided to check: i >produced myself a set of random numbers x_i with the condition >hammingdistance(x_i,x_j) >=10 instead of the numbers the random generator was >generating. in my test suite i run a depth 19 search on 80 positions and can >compare two different versions - result: no difference. while i did have small >changes like 101% or 99% in some test positions, it was never much and on >average just zero. i don't know if my condition above is stupid or if it doesnt >really matter. i think the condition is stupid, because you will only have a >real problem if x_i XOR x_j equals some other x_k. or if x_i XOR x_j XOR x_k >equals x_l XOR x_m etc. >looks like these conditions are kind of hard to check... i also think it doesnt It is not hard to check, it just takes a "long" time. >matter: another thing i did was to initialize rand() with different seeds and >see what happens. result: again zero. i'd like to see someone come up with hard >numbers showing that rand() is really bad for generating zobrist keys. i don't >believe it is. > >cheers > martin The primary reason why rand() is bad, is that it isn't portable, in that it is implementation defined. So when you move your program to another platform, you can't use the same numbers, i.e. for an opening book etc. Also, RAND_MAX can be all sorts of weird values, and finally no quality properties are guaranteed about rand(). All this, and the simplicity of making (copying) your own PRNG, makes me say that you should. /David
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