Author: Gerd Isenberg
Date: 04:35:03 12/24/02
Go up one level in this thread
On December 23, 2002 at 20:31:46, Bas Hamstra wrote:
>On December 23, 2002 at 19:33:50, Bas Hamstra wrote:
>
>>On December 23, 2002 at 19:07:51, Gerd Isenberg wrote:
>>
>>>On December 23, 2002 at 16:13:21, Bas Hamstra wrote:
>>>
>>>>Gerd,
>>>>
>>>>Those fill routines are really neat. I have a few tiny enhancements and am
>>>>working on more. How about this:
>>>>
>>>>// determine where white pawns can go safely, with a floodfill up:
>>>>WSafePath = FFillUp(WPawns, ~(AllPawns|BDominated) );
>>>>
>>>>// now we can calc "pawn-defendable" more accurately:
>>>>WDefendable = ((WPawnAttacksRight >> 16) & WSafePath) << 7 |
>>>> ((WPawnAttacksLeft >> 16) & WSafePath) << 9 ;
>>>>
>>>>// to be used in backward pawns:
>>>>WBackWard = ((~AllPawns & BDominated) >> 8) & WPawns & ~WDefendable;
>>>>
>>>>Best regards,
>>>>Bas.
>>>
>>>Hi Bas,
>>>
>>>Wow, absolutely great!!!
>>>Pawn-defendable is really more accurate.
>>>
>>>I guess FFillUp(g, p) is Steffan's FillUpOccluded and WPawns are therefore
>>>member of WSafePath.
>>
>>Yes, that is 100% correct. I played with this routines to check the speed of the
>>non-mmx versions, but it seems then I have a "wrap-around" problem?
>>
>>>BitBoard FFillUp(BitBoard g, BitBoard p)
>>>{
>>> g |= p & (g << 8);
>>> p &= (p << 8);
>>> g |= p & (g << 16);
>>> p &= (p << 16);
>>> return g | (p & (g << 32));
>>>}
>>>
>>>What do you think about (2.rank) pawns thay may push safely one step foreward,
>>>but became backward afterwards?
>>
>>Yes, I have been thinking about this too, but it gave me a headache :-) Because,
>>what to say about pawns that become backward if 3 squares advanced? What is the
>>definition of backward pawn, in fact? Is a pawn on the third rank counted as
>>backward if it would be backward if 2 squares advanced?
>>
>> WELL??
>>
>>:-)
>>
>>Best regards,
>>Bas.
>
Hi Bas,
Even if your code produces not exactly a set of backward pawns per definition, i
find the FillUpOccluded rather smart to get weak "backward like" pawns.
I agree with Russell and Bob here, don't worry about the exact definition.
A "real" backward pawn is a candidate (open pawn, no opposite pawn on stop- or
advanced stop squares) with a definitely weak stop square. Otherwise, if the
pawn is not open but not blocked, it is a disguised backward pawn by the
definition of Kmoch.
My current implementation is like
notDefendable[WHITE] = pawnBB[WHITE] & ~fillUp(pawnAttacks[WHITE]) & ...;
backWard1[WHITE] = notDefendable[WHITE] & (pawnDomination[BLACK] >> 8);
backWard2[WHITE] = backWard1[WHITE] & openPawns[WHITE];
But later i do a second pass, building a weaker notDefendable[WHITE] set,
excluding blocked and backWard defences in fillUp so far. Getting a kind of weak
pawn set with is similar to your definition.
I always exclude blocked widder pawns, duo pawns and hebel pawns from the
property being backward. But of course, none defendable widder pawns are also
most often weak.
I also consider white pawns on the 2.rank as "backward" or better weak, if they
may advance but are really backward afterwards. But the penalty is shlightly
smaller. No further steps, but i evaluate some vertical pawn fragmentation.
>- - - - - - - -
>- - B B B B - -
>- - - - - - - -
>- - - W W - - -
>- - - - - - - -
>- - - - - - - -
>- - - - - - - -
>- - - - - - - -
>
>Are these 2 white backward pawns? Neither can advance, neither be defended.
Because of duo pawns, no backward pawn here. But isolated duos may also
considered weak, due to the domination of the stop squares. Bur that's another
pattern, like "hängende Bauern":
- - - - - - - -
B B B - - B B B
- - - - - - - -
- - - - - - - -
- - - W W - - -
- - - - - - - -
W W - - - - W W
- - - - - - - -
If one advances, the other became backward:
- - - - - - - -
B B - - - B B B
- - B - - - - -
- - - - W - - -
- - - W - - - -
- - - - - - - -
W W - - - - W W
- - - - - - - -
or
- - - - - - - -
B B B - - - B B
- - - - - B - -
- - - W - - - -
- - - - W - - -
- - - - - - - -
W W - - - - W W
- - - - - - - -
>
>- - - - - - - -
>- - - B - - - -
>- - - - - - - -
>- - - - W - - -
>- - - - B - - -
>- - - - - - - -
>- - - W - - - -
>- - - - - - - -
>
>How many backward white pawns?
No real one. But d2 is a disguised backward.
All pawns should be considered weak.
But how much? If we shift d7 to f7, d2 becomes a real backward pawn with a
greater penalty. The weak e5 pawn is an advanced candidate. Even if the open,
backward-like penalty is greater than the disguised backward paenalty of d2, i
guess the value of e5 shuld be greater than d2. But may be i'm wrong here.
>
>- - - - - - - -
>- - - B - - - -
>- - - - - - - -
>- - - - - - - -
>- - - - - - - -
>- - - - - - - -
>- - - - W - - -
>- - - - - - - -
>
>Is this a backward white pawn? Can backward pawns ueberhaupt be isolated?
Yes, backward and isolated don't contradict. One could say both pawns are
candidates to get backward here. Pawns with this property on the backrank should
hurry to reach the 4. ro 5. rank to make the opponent backward. So a shlight
backrank (or 3.rank) penalty for candidates would be fine.
Regards,
Gerd
>
>I have had this more often. I keep seeing complications and eventually I don't
>even know what a backward pawn actually is and therefore chose a trivial
>definition. In books you typically see only this.
>
>- - - - - - - -
>- - - - - - B -
>- - - - - B - -
>- - - W - - - -
>- - - - W - - -
>- - - - - - - -
>- - - - - - - -
>- - - - - - - -
>
>
>
>Best regards,
>Bas.
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