Fix is_legal accepting non-canonical castling encodings#1096
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grepfuldead wants to merge 1 commit into
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Fix is_legal accepting non-canonical castling encodings#1096grepfuldead wants to merge 1 commit into
grepfuldead wants to merge 1 commit into
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is_legal derives the castling kind from to.file() == File::G alone and
never checks that to is the actual landing square, so with castling
rights and a clear path it accepts (king_from, arbitrary to, Castling)
for 63 bogus encodings per position. Playing one hits the unreachable
in get_castling_rook. Search is unaffected (UCI and the TT path only
see canonical encodings), but islegalperft feeds every accepted
encoding to make_move and currently panics on any position with
castling rights:
position fen r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R w KQkq - 0 1
islegalperft 1 -> panicked: entered unreachable code
Require to == kind.landing_square(), making is_legal an exact mirror
of generate_all_moves and restoring the diagnostic (kiwipete
islegalperft 1 now completes: 48). Matches the convention in Stockfish,
where special-move validity is generated-set membership.
No functional change.
Bench: 2526370
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is_legal derives the castling kind from to.file() == File::G alone and never checks that to is the actual landing square, so with castling rights and a clear path it accepts (king_from, arbitrary to, Castling) for 63 bogus encodings per position. Playing one hits the unreachable in get_castling_rook. Search is unaffected (UCI and the TT path only see canonical encodings), but islegalperft feeds every accepted encoding to make_move and currently panics on any position with castling rights:
Require to == kind.landing_square(), making is_legal an exact mirror of generate_all_moves and restoring the diagnostic (kiwipete islegalperft 1 now completes: 48). Matches the convention in Stockfish, where special-move validity is generated-set membership.
No functional change.
Bench: 2526370