Open Pawns (Bitboards)

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Open Pawns have no mechanical obstruction - an opponent pawn in front. They are at least half-free or even free passers. Thus, open pawns are a superset of passed pawns and half-free pawns like candidates but also weak pawns like the half-free straggler (backward pawn ) or half-free isolanis. Open pawns are vulnerable from opponent rook-attacks on half-open files.

=Open Single Pawn= Working in the square centric world of the board, thus using a square index of one particular pawn, likely from bitboard traversal, to lookup pre-calculated pattern.

For a single pawn we need to access a lookup-table to get all squares on the same file in front of the pawn. If the intersection of the fronspan with the set of opponent pawns is empty, it is a open pawn.

U64 arrFrontSpans[2][64];

if ( (arrFrontSpans[white][sqOfWhitePawn] & pawnBB[black]) == 0 ) -> pawn open

arrFrontSpan[white][d4] . . . 1 . . . . . . . 1 . . . . . . . 1 . . . . . . . 1 . . . . . . . p. . . . . . . . . . . . . . . . . . . . . . . . . . . . =Open Pawns set-wise= Working in the bitboard centric world to determine pawn related pattern set-wise.

Open Pawns have no mechanical obstruction in front - an opponent pawn as member of the own frontfill or frontspan. A relative complement with the opponents frontspans is sufficient to determine open pawns: U64 wOpenPawns(U64 wpawns, U64 bpawns) { return wpawns & ~bFrontSpan(bpawns); }

U64 bOpenPawns(U64 bpawns, U64 wpawns) { return bpawns & ~wFrontSpan(wpawns); }

=See also=
 * Candidates
 * Passed Pawns
 * Straggler
 * Unfree Pawns

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