Unfree+Pawns+(Bitboards)

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 * Home * Board Representation * Bitboards * Pawn Pattern and Properties * Unfree Pawns**

are pawns with a mechanical obstruction of an opponent pawn in front. Beeing an unfree pawn is therefor a mutual property for both white and black pawns on a **closed** file. Even if weak, like isolated or backward, **unfree** pawns are considered less vulnerable than open pawns on a halfopen file. Thus, in the initial position all pawns are unfree.
 * Unfree Pawns**, (Closed Pawns)

=Unfree 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 frontspan with the set of opponent pawns is not empty, it is an unfree or closed pawn.

code format="cpp" U64 arrFrontSpans[2][64];

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

code arrFrontSpan[white][d4] . . . 1 . . . . . . . 1 . . . . . . . 1 . . . . . . . 1 . . . . . . . p. . . . . . . . . . . . . . . . . . . . . . . . . . . . code

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

Unfree (or closed) Pawns have a mechanical obstruction in front - an opponent pawn as member of the own frontfill or frontspan. An intersection with opponents frontspans is sufficent to determine unfree pawns: code format="cpp" U64 wUnfreePawns(U64 wpawns, U64 bpawns) { return wpawns & bFrontSpan(bpawns); }

U64 bUnfreePawns(U64 bpawns, U64 wpawns) { return bpawns & wFrontSpan(wpawns); } code =External Links=
 * [|Pawn Power in Chess by Hans Kmoch - Glossary of Terms - Chess Forums] - [|Chess.com]
 * [|The Game of Chess: Pawns and Their Related Terms] from [|Just Chess .biz]

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