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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
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
there is a pawn in position to make an en passant capture.
is the position "behind" the pawn. This is recorded only if there is a pawn
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
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'));
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;
}
else