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FEN parsing: add a second check for correctly setting e.p. square

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Currently, we only check if there is a pawn in place
to make the en-passant capture. Now also check that
there is a pawn that could just have advanced two
squares. Also update the corresponding comment.

This makes the parsing of FENs a bit more robust, and
now correctly handles positions like the one reported by Dann Corbit.

position fen rnbqkb1r/ppp3pp/3p1n2/3P4/8/2P5/PP3PPP/RNBQKB1R w KQkq e6
d

 +---+---+---+---+---+---+---+---+
 | r | n | b | q | k | b |   | r |
 +---+---+---+---+---+---+---+---+
 | p | p | p |   |   |   | p | p |
 +---+---+---+---+---+---+---+---+
 |   |   |   | p |   | n |   |   |
 +---+---+---+---+---+---+---+---+
 |   |   |   | P |   |   |   |   |
 +---+---+---+---+---+---+---+---+
 |   |   |   |   |   |   |   |   |
 +---+---+---+---+---+---+---+---+
 |   |   | P |   |   |   |   |   |
 +---+---+---+---+---+---+---+---+
 | P | P |   |   |   | P | P | P |
 +---+---+---+---+---+---+---+---+
 | R | N | B | Q | K | B |   | R |
 +---+---+---+---+---+---+---+---+

Fen: rnbqkb1r/ppp3pp/3p1n2/3P4/8/2P5/PP3PPP/RNBQKB1R w KQkq - 0 1

No functional change.
This commit is contained in:
joergoster 2016-11-09 16:42:27 +01:00 • committed by Marco Costalba
parent dc4655e1f9
commit de269ee18e
1 changed files with 5 additions and 3 deletions
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8
src/position.cpp
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@ -176,8 +176,9 @@ Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Th
4) En passant target square (in algebraic notation). If there's no en passant 4) En passant target square (in algebraic notation). If there's no en passant
target square, this is "-". If a pawn has just made a 2-square move, this target square, this is "-". If a pawn has just made a 2-square move, this
is the position "behind" the pawn. This is recorded regardless of whether is the position "behind" the pawn. This is recorded only if there is a pawn
there is a pawn in position to make an en passant capture. in position to make an en passant capture, and if there really is a pawn
that might have advanced two squares.
5) Halfmove clock. This is the number of halfmoves since the last pawn advance 5) Halfmove clock. This is the number of halfmoves since the last pawn advance
or capture. This is used to determine if a draw can be claimed under the or capture. This is used to determine if a draw can be claimed under the
@ -254,7 +255,8 @@ Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Th
{ {
st->epSquare = make_square(File(col - 'a'), Rank(row - '1')); st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
if (!(attackers_to(st->epSquare) & pieces(sideToMove, PAWN))) if ( !(attackers_to(st->epSquare) & pieces(sideToMove, PAWN))
|| !(pieces(~sideToMove, PAWN) & (st->epSquare + pawn_push(~sideToMove))))
st->epSquare = SQ_NONE; st->epSquare = SQ_NONE;
} }
else else