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GerdIsenberg
Feb 27, 2015
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**[[Home]] * [[Board Representation]] * [[Bitboards]] * [[Pawn Pattern and Properties]] * Defended Pawns**
Working in the bitboard centric world to determine pawn related pattern set-wise.
Each pawn, member of the own [[Pawn Attacks (Bitboards)|pawn attack set]] is obviously defended by a pawn, thus likely not a winning capture target for opponent pieces (except pawns). If a defended pawn is [[Open Pawns (Bitboards)|open]], opponent rooks on [[Pawns and Files (Bitboards)#HalfopenFiles|half-open]] files bang one's head against a brick wall.
[[#Defended]]
=Defended=
Again, it is advantageous to keep disjoint east-west attack sets for a unique 1:1 source-target relationship. On demand we can use the union or intersection on the fly. Note that attack direction is related to the target square. East attack is from south/north-west to north/south-east
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white pawns defended defended
from west -> from east <-
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[[code format="cpp"]]
U64 wPawnDefendedFromWest(U64 wpawns) {
return wpawns & wPawnEastAttacks(wpawns);
}
U64 wPawnDefendedFromEast(U64 wpawns) {
return wpawns & wPawnWestAttacks(wpawns);
}
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[[#Defenders]]
=Defenders=
To get the set of defenders on the fly, we use the intersection of white pawns with it's "black" attacks:
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white pawns defenders defenders
from west from east
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[[code format="cpp"]]
U64 wPawnDefendersFromWest(U64 wpawns) {
return wpawns & bPawnWestAttacks(wpawns);
}
U64 wPawnDefendersFromEast(U64 wpawns) {
return wpawns & bPawnEastAttacks(wpawns);
}
[[code]]
Otherwise, if the set of defenders was already determined (or vice versa), we can already take advantage of the unique target/source relation ship:
[[code format="cpp"]]
wPawnDefendersFromWest = wPawnDefendedFromWest >> 9;
wPawnDefendersFromEast = wPawnDefendedFromEast >> 7;
[[code]]
[[#DefendedDefenders]]
=Defended Defenders=
Defended defenders already are the inner pawns of a at least [[Pawn chain|triple-chain]], the d5 pawn for instance:
[[code]]
white pawns defended defended
from west from east
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white pawns defenders defenders
from west from east
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defenders and defenders and
white pawns defended defended
from west from east
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[[#NotDefendedDefenders]]
=Not Defended Defenders=
Not defended defenders are the base of a [[Pawn chain|chain]] - target of opponent attacks:
[[code]]
not defended not defended
white pawns defenders defenders
from west from east
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[[#NotDefendingDefended]]
=Not Defending Defended=
Defended pawns not defending other pawns are likely the peak of a [[Pawn chain|chain]].
[[code]]
not defending not defending
white pawns defended defended
from west from east
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=Forum Posts=
* [[http://www.talkchess.com/forum/viewtopic.php?t=55477|pattern coding in bitboards]] by [[Pawel Koziol]], [[CCC]], February 26, 2015 ยป [[Pawn chain]]
=What links here?=
[[include page="Defended Pawns (Bitboards)" component="backlinks" limit="10" ]]
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