Passed Pawns (Bitboards)

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A Passed Pawn, also called Passer, has no opponent pawns in front on the same or adjacent files. In Bitboards, passers may be determined square- or set-wise. =Single Passer= 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 and adjacent file in front of the pawn. This is what we call front-span and attack spans. If the intersection of those span-union with the set of opponent pawns is empty, it is a passed pawn. U64 arrFrontSpans[2][64];

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

arrFrontSpans[white][d4] . . 1 1 1 . . . . . 1 1 1 . . . . . 1 1 1 . . . . . 1 1 1 . . . . . . p. . . . . . . . . . . . . . . . . . . . . . . . . . . . Pawns ready to promote don't need above condition, the appearance on the 7th (or 2nd) rank is already sufficient to be a passer: if ( sqOfWhitePawn >= a7 ) -> white pawn may promote if ( sqOfBlackPawn <= h2 ) -> black pawn may promote

=Passers set-wise= Working in the bitboard centric world to determine pawn related pattern set-wise.

Passers are the pawns outside the union of all opponent frontspans and attack-frontspans.

U64 wPassedPawns(U64 wpawns, U64 bpawns) { U64 allFrontSpans = bFrontSpans(bpawns); allFrontSpans |= eastOne(allFrontSpans) | westOne(allFrontSpans); return wpawns & ~allFrontSpans; }

U64 bPassedPawns(U64 bpawns, U64 wpawns) { U64 allFrontSpans = wFrontSpans(wpawns); allFrontSpans |= eastOne(allFrontSpans) | westOne(allFrontSpans); return bpawns & ~allFrontSpans; }

=See also=
 * Candidate Passed Pawn
 * Candidates (Bitboards)
 * Hidden Passed Pawn
 * Passed Pawn
 * Passed Pawn Extensions
 * Set-wise Rule of Squares

=External Links=
 * Passed pawn from Wikipedia

=References=

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