Author: Dan Newman
Date: 18:47:01 02/12/02
Go up one level in this thread
On February 12, 2002 at 17:42:53, Miguel A. Ballicora wrote:
>On February 12, 2002 at 16:16:54, Dan Newman wrote:
>
>>On February 12, 2002 at 10:55:09, Miguel A. Ballicora wrote:
>>
>>>On February 11, 2002 at 19:21:18, Ralf Elvsén wrote:
>>>
>>>>On February 10, 2002 at 19:49:01, Miguel A. Ballicora wrote:
>>>>
>>>>>I never understood what the people is doing with the mate values, I always
>>>>>get confused. I am glad that I came up with my own approach before I asked or
>>>>>saw any post about it. :-)
>>>>>
>>>>>What I do in pseudo code in Gaviota is
>>>>>
>>>>>search (alpha, beta)
>>>>>{
>>>>> adjust_in (&alpha, &beta); /* increments alpha += 1 and beta += 1 if they
>>>>> are positive mate values, do the opposite if
>>>>> it is a negative mate value */
>>>>> probe_hashtables_normally()
>>>>>
>>>>> loop { /* normal alpha beta stuff */
>>>>> makemove();
>>>>> value = search_moves_for_best_value(-beta, -alpha);
>>>>> unmakemove();
>>>>> best = keep the best value;
>>>>> }
>>>>>
>>>>> store_in_hashtables_normally();
>>>>>
>>>>> adjust_out(&best); /* decrement best -= 1 if it is a +mate value
>>>>> increment +=1 if it is a -mate value */
>>>>> return best;
>>>>>
>>>>>}
>>>>>
>>>>>And basically, I do not do anything else. I store in the hashtables without
>>>>>any change. adjust_out() it is used too when I return early.
>>>>>
>>>>>Regards,
>>>>>Miguel
>>>>
>>>>Here's another one who is doing the same thing :) It is really
>>>>simple and clear. My functions are called "upstep" and "downstep" :)
>>>>
>>>>Ralf
>>>
>>>Good! Then I am not crazy. At least I am not alone in the nuthouse. :-)
>>>
>>>Regards,
>>>Miguel
>>
>>I tried something like this in Shrike last year, but ran into trouble.
>>The idea I had was to have the mate-in-n scores at a node really mean
>>mate-in-n from that node. Then, I thought, I could just store the
>>scores without adjustment in the hash table. (And it made more
>>sense to me as well.)
>>
>>I also realized that alpha and beta mate-in-n scores needed to be
>>adjusted too. That is (I think) where I had the trouble. I ended
>>up with bound scores that were oustide the [-32768,+32767] range
>
>BTW, I think is a bad idea to allow -32768. That is not a valid 16 bit value
>accepted by the C standard and it might work on some implementations and not in
>others. That number can give you some headaches with some operations.
>It is much safer to use a portable range -32767, +32767.
>
Actually, my MIN_SCORE is -32767 (for symmetry), but my program doesn't
break until the score goes below -32768--at least on the PC. I guess
that other processors could use something other than twos-complement,
though I haven't heard of anything like that recently... I think perhaps
some early computers used ones-complement, or sign magnitude. (In fact
I heard a rumor of a ternary machine (Russian I think) years ago...)
>>that is allowable in my program. This caused my hash table
>>entries to become corrupted (since I stuff the score into half
>>a 32-bit word by first adding 32768 to it and then ORing the
>>result in). The out-of-range error happens because a mate-in-n
>>bound can end up being incremented more than n times.
>>
>>Anyway, I gave up and put things back the way they were. After
>>seeing that others have done this successfully I think I'll have
>>to try it again...
>>
>>-Dan.
>
>At the beginning of search I do exactly
>
>alpha = adjust_in(alpha);
>beta = adjust_in(beta);
>
>where the declaration is exactly:
>
>static eval_t
>adjust_in (eval_t x)
>{
> if (MATE100_VALUE < x && x < MATE_VALUE)
> return x + 1;
> if (-MATE_VALUE < x && x < -MATE100_VALUE)
> return x - 1;
> return x;
>}
>
>The value cannot be adjusted if it is MATE_VALUE.
>Nowhere in my program I allowed a value that is supposed to be a score
>to be out of range. I have ASSERT() everywhere checking this.
>I think that this should be enough. adjust_out() is just a simmetric function
>and as I said, every time I return I use that. That's all.
>
>Regards,
>Miguel
Thanks, I'll have to try that sometime. I think I didn't try this before
because at the time it seemed like a mistake to me to clip the bounds in
that fashion, but I guess it makes sense since nothing's better than mate...
-Dan.
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