Difference between revisions of "Open Pawns (Bitboards)"
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Revision as of 12:24, 10 May 2018
Home * Board Representation * Bitboards * Pawn Pattern and Properties * Open Pawns
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); }