Author: Robert Hyatt
Date: 21:20:07 12/23/02
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.
>
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>Are these 2 white backward pawns? Neither can advance, neither be defended.
>
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>How many backward white pawns?
In your first example, both are weak, but not backward. In your second,
both are backward but the e pawn is weaker because it is on a half-open
file while the d-pawn is not so easy to get to. Of course, black has
similar weak pawns. :)
A "backward" pawn is a pawn that can't advance without being captured by
an enemy pawn, and it is not defendable by a friendly pawn. The classic
example is white pawns on d3 and e4 and a black pawn on e5. The white pawn
on d3 is backward. Backward pawns are _generally_ on half-open files so that
they can be attacked from the front by enemy rooks, which makes them even
weaker.
A backward pawn is really just a specific example of a weak pawn. For
example black has pawns at c5 and e5. White has a pawn at d3 and e3.
The white pawn can't advance as it would be attacked by two pawns and defended
by one, and it would go lost unless white piles up enough pieces to make that
pawn push doable, which would tie up pieces and give black a chance to start
action somewhere else.
>
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>Is this a backward white pawn? Can backward pawns ueberhaupt be isolated?
No. But again, backward is just one sub-class of weak. Isolated pawns are
another sub-class of weak.
>
>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.
>
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>
>
>Best regards,
>Bas.
Ignore backward and catch the weak pawns instead, as that will include
backward and a large group of other types of weak pawns that are not
backward.
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