Author: Tim Foden
Date: 09:13:15 12/18/00
Go up one level in this thread
On December 18, 2000 at 10:37:28, Ulrich Tuerke wrote:
>On December 18, 2000 at 09:39:19, Tim Foden wrote:
>
>>On December 18, 2000 at 07:46:55, Ulrich Tuerke wrote:
>>
>>>Forget my remarks. If this was your problem, you would probably not reach so
>>>high iterations. (Comet ususally solves this on iteration #18.)
>>>I guess that rather your algo has a bug.
>>
>>I think you may well be right. I could try stripping *everything* out of the
>>search and the evaluation function, except the hash table and material
>>evaluation.
>>
>>Should the FINE 70 position still be solved with such a search?
>>
>>>
>>>Sorry, Uli
>>
>>No problem... any ideas are appreciated. :)
>>
>>Cheers, Tim.
>
>I should rather think that it's the hashing itself which could make the problem.
>My 1st idea is that you could make a mistake regarding bounds. May be you store
>a bound as an exact value, or you read a bound and interprete as exact ?
>Perhaps it's worthwhile to test what happens if you store and read exact values
>only.
>
>Uli
You might be right about this. Looking at the code I'm not really sure. I'll
look at it in more detail, but in the mean time here is a copy of the relevant
bits:
Here is my current code for reading from hash table...
//
// look in the hash table to help us with the search
//
CHashTableRec* pRec;
m_nTTProbes++;
if( CHashTable::Lookup(pRec) )
{
m_nTTHits++;
int scoreType = pRec->GetScoreType();
int eval = pRec->GetValue();
// check if it would be futile to do a null move
if( scoreType == CHashTableRec::flagScoreIsFailLow &&
depth - NULL_MOVE_REDUCTION - PLY <= pRec->GetDepth() &&
eval < beta )
doNull = false;
if( pRec->GetDepth() >= depth )
{
m_nTTUsed++;
switch( scoreType )
{
case CHashTableRec::flagScoreIsExact:
if( abs(eval) > evalWin )
{
if( eval > 0 )
eval -= ply;
else
eval += ply;
}
m_pvhash[ply] = CBoard::Hash();
return eval;
case CHashTableRec::flagScoreIsFailHigh:
if( eval >= beta )
{
return eval;
}
break;
case CHashTableRec::flagScoreIsFailLow:
if( eval <= alpha )
{
return eval;
}
break;
}
}
m_searchInfo[ply].m_hashMove = pRec->GetMoveToTry();
}
And now storing in the hash table...
//
// store the results in the hash table
//
int flags;
int score = alpha;
if( alpha <= initialAlpha ) // actually can not be smaller
{
flags = CHashTableRec::flagScoreIsFailLow;
score = initialAlpha;
}
else if( alpha >= initialBeta ) // normally can not be greater
{
flags = CHashTableRec::flagScoreIsFailHigh;
score = initialBeta;
}
else
{
flags = CHashTableRec::flagScoreIsExact;
if( abs(score) > evalWin )
{
if( score > 0 )
score += ply;
else
score -= ply;
DBG_ASSERT( abs(score) <= evalCheckmate );
}
}
Cheers, Tim.
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