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Subject: Re: Rybka code

Author: Chrilly Donninger

Date: 06:12:59 12/12/05

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>>>>
>>>>You have access to Rybka's source codes?
>>>
>>>Everyone has of any programms he owns the detailed source-code. After all the
>>>Intel processor must also know what to do. Its just a matter if you can read
>>>assembly code or not.
>>>The code from where I know that Rybka uses PVS:
>>>
>>>.text:0040D156                 call    sub_40D1B0
>>>.text:0040D15B                 mov     esi, eax
>>>.text:0040D15D                 lea     eax, [esp+278h+var_238]
>>>.text:0040D161                 push    eax
>>>.text:0040D162                 push    edi
>>>.text:0040D163                 neg     esi
>>>.text:0040D165                 call    sub_40A780
>>>.text:0040D16A                 add     esp, 18h
>>>.text:0040D16D                 cmp     esi, [esp+268h+var_25C]
>>>.text:0040D171                 jle     short loc_40D183
>>>.text:0040D173                 cmp     esi, ebx
>>>.text:0040D175                 mov     [esp+268h+var_25C], esi
>>>.text:0040D179                 jle     short loc_40D183
>>>.text:0040D17B                 cmp     esi, [ebp+arg_4]
>>>.text:0040D17E                 mov     [ebp+arg_0], esi
>>>.text:0040D181                 jge     short loc_40D13A
>>>
>>
>>Can i ask what program are you using to produce this text from Rybka's exe?
>
>I think any disassembler will do.

Yes, up to this level and dissassembly does. But if you really want to know the
function of this code, IDA-Pro helps a lot. One of the few pieces of software I
am really impressed. It took me 5 minutes to spot the search code in Rybka and
after 1 hour I could read this part as
val=-QuiesenceSearch()
UndoMove()
if(val>bestval) { bestval=val; }
if(val>alpha) { alpha=val; }
if(val>=beta) { return val; }

Well, and then you know it can't be MTD(), because MTD uses a Zero-width window
and the update of alpha makes in MTD no sence. Actually, beta (or alpha) is not
necessary at all.

Chrilly



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