Author: Robert Hyatt
Date: 13:29:53 12/13/05
Go up one level in this thread
On December 13, 2005 at 11:52:03, Álvaro Begué wrote:
>On December 13, 2005 at 08:47:51, Chrilly Donninger wrote:
>
>>Just for the curious, below is the code for the Rybka-Mate bug. I have seen
>>another bug in the Beta-Code too. There are in every programm hundreds of bugs,
>>so it would be more surprising to say: I have seen no other bug.
>>
>>.text:0040CD07 mov ebp, [esp+868h+var_854]
>>.text:0040CD0B cmp ebp, 0FFFF810Ch
>>.text:0040CD11 mov dword_667A14, edi
>>.text:0040CD17 jnz loc_40CDCA
>>.text:0040CD1D mov eax, [esp+868h+arg_C]
>>.text:0040CD24 neg al
>>.text:0040CD26 pop edi
>>.text:0040CD27 pop ebx
>>.text:0040CD28 pop esi
>>.text:0040CD29 pop ebp
>>.text:0040CD2A sbb eax, eax
>>.text:0040CD2C and eax, 0FFFF8300h
>>.text:0040CD31 add esp, 858h
>>.text:0040CD37 retn
>>
>>In C this reads as:
>>if(Bestscore == -32500( // No legal move found
>> if(InCheck) {
>> return -32000;
>> }
>> else { // Stalemate
>> return 0;
>> }
>>}
>>
>>The bug is, that all mates are the same. In fact shorter mates are better for
>>the mate-giving side (or worse for the mated side) than longer mates. One has to
>>subtract the Plies/Distance from the starting position.
>>The bug is in my opinion a consequence of a bad design decision. There are 2
>>different "minus-infinite" values. In BestScore minus infinite is -32500, for
>>mate its -32000. If one sets bestscore at the first place to -32000+Ply one gets
>>cleaner and more efficient code and avoids the bug.
>>I had the same bug in Nimzo 1.0. But I must admit, that Rybka 1.0 is stronger.
>>
>>Chrilly
>
>
>I use the exact same solution that Chrilly proposes, combined with the "store
>only bounds for mating scores in the hash table" idea that I picked from Bruce
>Moreland's website. As far as I can tell, it works great.
>
>Álvaro.
The question is "why store only bounds"? Makes no sense to me. I've always
stored exact (corrected for distance to root) for mate scores. Allows me to
store all the EGTB mates as well.
Never understood the reasoning for not storing exact mate scores. Never had a
single problem doing so in either of my programs, spanning _many_ years...
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