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Impossible en passant capture that blocks a check #19

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Impossible en passant capture that blocks a check #19

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0bbc398
Add a tag for perft tests
veloce Apr 15, 2023
4a291b8
Fix en passant capture when blocking sliding check
veloce Apr 15, 2023
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31 changes: 27 additions & 4 deletions lib/src/position.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -844,9 +844,20 @@ abstract class Position<T extends Position<T>> {
}
if (epSquare != null && _canCaptureEp(square)) {
final pawn = epSquare! - delta;

if (ctx.checkers.isEmpty || ctx.checkers.singleSquare == pawn) {
legalEpSquare = SquareSet.fromSquare(epSquare!);
}

// en passant capture is valid when blocking a sliding attack on king
final sniper = ctx.snipers.singleSquare;
if (ctx.checkers.isNotEmpty && sniper != null) {
final b = between(ctx.king!, sniper);
final epSquareSet = SquareSet.fromSquare(epSquare!);
if ((b & board.occupied).isEmpty && b.isIntersected(epSquareSet)) {
legalEpSquare = epSquareSet;
}
}
}
} else if (piece.role == Role.bishop) {
pseudo = bishopAttacks(square, board.occupied);
Expand Down Expand Up @@ -899,24 +910,30 @@ abstract class Position<T extends Position<T>> {
isVariantEnd: isVariantEnd,
mustCapture: false,
king: king,
snipers: SquareSet.empty,
blockers: SquareSet.empty,
checkers: SquareSet.empty);
}
final snipers = _snipers(king);
return _Context(
isVariantEnd: isVariantEnd,
mustCapture: false,
king: king,
blockers: _sliderBlockers(king),
snipers: snipers,
blockers: _sliderBlockers(king, snipers),
checkers: checkers,
);
}

SquareSet _sliderBlockers(Square king) {
final snipers = rookAttacks(king, SquareSet.empty)
SquareSet _snipers(Square king) {
return rookAttacks(king, SquareSet.empty)
.intersect(board.rooksAndQueens)
.union(bishopAttacks(king, SquareSet.empty)
.intersect(board.bishopsAndQueens))
.intersect(board.bySide(turn.opposite));
}

SquareSet _sliderBlockers(Square king, SquareSet snipers) {
SquareSet blockers = SquareSet.empty;
for (final sniper in snipers.squares) {
final b = between(king, sniper) & board.occupied;
Expand Down Expand Up @@ -1754,11 +1771,13 @@ class RacingKings extends Position<RacingKings> {
return blackKing != null &&
kingAttacks(blackKing).intersect(goal).squares.where((square) {
// Check whether this king move is legal
final snipers = _snipers(blackKing);
final context = _Context(
isVariantEnd: false,
mustCapture: false,
king: blackKing,
blockers: _sliderBlockers(blackKing),
snipers: snipers,
blockers: _sliderBlockers(blackKing, snipers),
checkers: checkers,
);
final legalMoves = _legalMovesOf(blackKing, context: context);
Expand Down Expand Up @@ -2537,6 +2556,7 @@ class _Context {
const _Context({
required this.isVariantEnd,
required this.king,
required this.snipers,
required this.blockers,
required this.checkers,
required this.mustCapture,
Expand All @@ -2545,20 +2565,23 @@ class _Context {
final bool isVariantEnd;
final bool mustCapture;
final Square? king;
final SquareSet snipers;
final SquareSet blockers;
final SquareSet checkers;

_Context copyWith({
bool? isVariantEnd,
bool? mustCapture,
Square? king,
SquareSet? snipers,
SquareSet? blockers,
SquareSet? checkers,
}) {
return _Context(
isVariantEnd: isVariantEnd ?? this.isVariantEnd,
mustCapture: mustCapture ?? this.mustCapture,
king: king,
snipers: snipers ?? this.snipers,
blockers: blockers ?? this.blockers,
checkers: checkers ?? this.checkers,
);
Expand Down
71 changes: 36 additions & 35 deletions test/perft_test.dart
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
@Tags(['perft'])
import 'package:test/test.dart';
import 'dart:io';
import 'package:dartchess/dartchess.dart';
Expand Down Expand Up @@ -103,41 +104,6 @@ void main() async {
}
});

// group('Chess Tricky', () {
// final tests =
// Parser().parse(File('test/resources/tricky.perft').readAsStringSync());
// for (final perftTest in tests) {
// for (final testCase in perftTest.cases
// .takeWhile((testCase) => testCase.nodes < nodeLimit)) {
// test('${perftTest.id} ${perftTest.fen} ${testCase.depth}', () {
// final position = Chess.fromSetup(Setup.parseFen(perftTest.fen),
// ignoreImpossibleCheck:
// true); // true: otherwise there is an Impossible Check Error
// expect(perft(position, testCase.depth), testCase.nodes,
// reason:
// 'id: ${perftTest.id}\nfen: ${perftTest.fen} \ndepth: ${testCase.depth} \nnodes: ${testCase.nodes}');
// });
// }
// }
// });

group('Random', () {
final tests =
Parser().parse(File('test/resources/random.perft').readAsStringSync());
// only test 10 position in random. Test file has around 6000 positions
for (final perftTest in tests.take(50)) {
final position = Chess.fromSetup(Setup.parseFen(perftTest.fen));
for (final testCase in perftTest.cases
.takeWhile((testCase) => testCase.nodes < nodeLimit)) {
test('${perftTest.id} ${perftTest.fen} ${testCase.depth}', () {
expect(perft(position, testCase.depth), testCase.nodes,
reason:
'id: ${perftTest.id}\nfen: ${perftTest.fen} \ndepth: ${testCase.depth} \nnodes: ${testCase.nodes}');
});
}
}
});

group('Standard', () {
test('initial position', () {
const pos = Chess.initial;
Expand All @@ -147,6 +113,41 @@ void main() async {
expect(perft(pos, 3), 8902);
expect(perft(pos, 4), 197281);
});

group('random', () {
final tests = Parser()
.parse(File('test/resources/random.perft').readAsStringSync());
// only test 10 position in random. Test file has around 6000 positions
for (final perftTest in tests.take(50)) {
final position = Chess.fromSetup(Setup.parseFen(perftTest.fen));
for (final testCase in perftTest.cases
.takeWhile((testCase) => testCase.nodes < nodeLimit)) {
test('${perftTest.id} ${perftTest.fen} ${testCase.depth}', () {
expect(perft(position, testCase.depth), testCase.nodes,
reason:
'id: ${perftTest.id}\nfen: ${perftTest.fen} \ndepth: ${testCase.depth} \nnodes: ${testCase.nodes}');
});
}
}
});

group('tricky', () {
final tests = Parser()
.parse(File('test/resources/tricky.perft').readAsStringSync());
for (final perftTest in tests) {
for (final testCase in perftTest.cases
.takeWhile((testCase) => testCase.nodes < nodeLimit)) {
test('${perftTest.id} ${perftTest.fen} ${testCase.depth}', () {
final position = Chess.fromSetup(Setup.parseFen(perftTest.fen),
ignoreImpossibleCheck:
true); // true: otherwise there is an Impossible Check Error
expect(perft(position, testCase.depth), testCase.nodes,
reason:
'id: ${perftTest.id}\nfen: ${perftTest.fen} \ndepth: ${testCase.depth} \nnodes: ${testCase.nodes}');
});
}
}
});
});

group('Chess 960', () {
Expand Down