Isolated Pawns (Bitboards)
Home * Board Representation * Bitboards * Pawn Pattern and Properties * Isolated Pawns
An Isolated Pawn or Isolani has no friendly pawns on adjacent files. Isolanis may be determined inside the square centric world as well in set-wise world of Bitboards considering the whole board.
Isolani by Square
To determine whether a pawn is isolated, we simply lookup an array with neighboring file-masks. If the intersection of neighbored files with own pawns is empty, the pawn is isolated. This symmetrical property appears to be equal for white and black pawns.
if ( (arrNeighborFiles[sqOfWhitePawn] & pawnBB[white]) == 0 ) -> pawn is isolated
arrNeighborFiles[d*] . . 1 . 1 . . . . . 1 . 1 . . . . . 1 . 1 . . . . . 1 . 1 . . . . . 1 . 1 . . . . . 1 . 1 . . . . . 1 . 1 . . . . . 1 . 1 . . .
The arrNeighborFiles might be condensed to eight bitboards only, instead of 64 - if we index by
file(sq) == sq & 7
instead of square.
Isolanis and Half-isolanis set-wise
Isolated pawns are the relative complement of pawns with the union of their own attack fills over the whole file. To keep disjoint pawns with no neighbor on either east or west adjacent files has the advantage of greater versatility. Isolanis are the intersection of them, half-isolanis the exclusive or:
U64 noNeighborOnEastFile (U64 pawns) {
return pawns & ~westAttackFileFill(pawns);
}
U64 noNeighborOnWestFile (U64 pawns) {
return pawns & ~eastAttackFileFill(pawns);
}
U64 isolanis(U64 pawns) {
return noNeighborOnEastFile(pawns)
& noNeighborOnWestFile(pawns);
}
U64 halfIsolanis(U64 pawns) {
return noNeighborOnEastFile(pawns)
^ noNeighborOnWestFile(pawns);
}
Hanging pawns
Hanging pawns are a duo of open and half-isolated pawns.
U64 wHangingPawns(U64 wpawns, U64 bpawns) {
return wOpenPawns(wpawns, bpawns)
& halfIsolanis(wpawns) & duo(wpawns);
}
