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
References
- ↑ Pawn's Dream 2009 by Carina Jørgensen