-
Notifications
You must be signed in to change notification settings - Fork 472
/
position.cpp
1281 lines (954 loc) · 39 KB
/
position.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <algorithm>
#include <cassert>
#include <cstring>
#include <iomanip>
#include <sstream>
#include "bitcount.h"
#include "misc.h"
#include "movegen.h"
#include "position.h"
#include "psqtab.h"
#include "thread.h"
#include "tt.h"
#include "uci.h"
using std::string;
Value PieceValue[PHASE_NB][PIECE_NB] = {
{ VALUE_ZERO, PawnValueMg, KnightValueMg, BishopValueMg, RookValueMg, QueenValueMg },
{ VALUE_ZERO, PawnValueEg, KnightValueEg, BishopValueEg, RookValueEg, QueenValueEg } };
namespace Zobrist {
Key psq[COLOR_NB][PIECE_TYPE_NB][SQUARE_NB];
Key enpassant[FILE_NB];
Key castling[CASTLING_RIGHT_NB];
Key side;
Key exclusion;
}
Key Position::exclusion_key() const { return st->key ^ Zobrist::exclusion;}
namespace {
const string PieceToChar(" PNBRQK pnbrqk");
Score psq[COLOR_NB][PIECE_TYPE_NB][SQUARE_NB];
// min_attacker() is a helper function used by see() to locate the least
// valuable attacker for the side to move, remove the attacker we just found
// from the bitboards and scan for new X-ray attacks behind it.
template<int Pt> FORCE_INLINE
PieceType min_attacker(const Bitboard* bb, const Square& to, const Bitboard& stmAttackers,
Bitboard& occupied, Bitboard& attackers) {
Bitboard b = stmAttackers & bb[Pt];
if (!b)
return min_attacker<Pt+1>(bb, to, stmAttackers, occupied, attackers);
occupied ^= b & ~(b - 1);
if (Pt == PAWN || Pt == BISHOP || Pt == QUEEN)
attackers |= attacks_bb<BISHOP>(to, occupied) & (bb[BISHOP] | bb[QUEEN]);
if (Pt == ROOK || Pt == QUEEN)
attackers |= attacks_bb<ROOK>(to, occupied) & (bb[ROOK] | bb[QUEEN]);
attackers &= occupied; // After X-ray that may add already processed pieces
return (PieceType)Pt;
}
template<> FORCE_INLINE
PieceType min_attacker<KING>(const Bitboard*, const Square&, const Bitboard&, Bitboard&, Bitboard&) {
return KING; // No need to update bitboards: it is the last cycle
}
} // namespace
/// CheckInfo c'tor
CheckInfo::CheckInfo(const Position& pos) {
Color them = ~pos.side_to_move();
ksq = pos.king_square(them);
pinned = pos.pinned_pieces(pos.side_to_move());
dcCandidates = pos.discovered_check_candidates();
checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
checkSq[KING] = 0;
}
/// operator<<(Position) returns an ASCII representation of the position
std::ostream& operator<<(std::ostream& os, const Position& pos) {
os << "\n +---+---+---+---+---+---+---+---+\n";
for (Rank r = RANK_8; r >= RANK_1; --r)
{
for (File f = FILE_A; f <= FILE_H; ++f)
os << " | " << PieceToChar[pos.piece_on(make_square(f, r))];
os << " |\n +---+---+---+---+---+---+---+---+\n";
}
os << "\nFen: " << pos.fen() << "\nKey: " << std::hex << std::uppercase
<< std::setfill('0') << std::setw(16) << pos.st->key << std::dec << "\nCheckers: ";
for (Bitboard b = pos.checkers(); b; )
os << UCI::square(pop_lsb(&b)) << " ";
return os;
}
/// Position::init() initializes at startup the various arrays used to compute
/// hash keys and the piece square tables. The latter is a two-step operation:
/// Firstly, the white halves of the tables are copied from PSQT[] tables.
/// Secondly, the black halves of the tables are initialized by flipping and
/// changing the sign of the white scores.
void Position::init() {
PRNG rng(1070372);
for (Color c = WHITE; c <= BLACK; ++c)
for (PieceType pt = PAWN; pt <= KING; ++pt)
for (Square s = SQ_A1; s <= SQ_H8; ++s)
Zobrist::psq[c][pt][s] = rng.rand<Key>();
for (File f = FILE_A; f <= FILE_H; ++f)
Zobrist::enpassant[f] = rng.rand<Key>();
for (int cr = NO_CASTLING; cr <= ANY_CASTLING; ++cr)
{
Bitboard b = cr;
while (b)
{
Key k = Zobrist::castling[1ULL << pop_lsb(&b)];
Zobrist::castling[cr] ^= k ? k : rng.rand<Key>();
}
}
Zobrist::side = rng.rand<Key>();
Zobrist::exclusion = rng.rand<Key>();
for (PieceType pt = PAWN; pt <= KING; ++pt)
{
PieceValue[MG][make_piece(BLACK, pt)] = PieceValue[MG][pt];
PieceValue[EG][make_piece(BLACK, pt)] = PieceValue[EG][pt];
Score v = make_score(PieceValue[MG][pt], PieceValue[EG][pt]);
for (Square s = SQ_A1; s <= SQ_H8; ++s)
{
psq[WHITE][pt][ s] = (v + PSQT[pt][s]);
psq[BLACK][pt][~s] = -(v + PSQT[pt][s]);
}
}
}
/// Position::operator=() creates a copy of 'pos'. We want the new born Position
/// object to not depend on any external data so we detach state pointer from
/// the source one.
Position& Position::operator=(const Position& pos) {
std::memcpy(this, &pos, sizeof(Position));
startState = *st;
st = &startState;
nodes = 0;
assert(pos_is_ok());
return *this;
}
/// Position::clear() erases the position object to a pristine state, with an
/// empty board, white to move, and no castling rights.
void Position::clear() {
std::memset(this, 0, sizeof(Position));
startState.epSquare = SQ_NONE;
st = &startState;
for (int i = 0; i < PIECE_TYPE_NB; ++i)
for (int j = 0; j < 16; ++j)
pieceList[WHITE][i][j] = pieceList[BLACK][i][j] = SQ_NONE;
}
/// Position::set() initializes the position object with the given FEN string.
/// This function is not very robust - make sure that input FENs are correct,
/// this is assumed to be the responsibility of the GUI.
void Position::set(const string& fenStr, bool isChess960, Thread* th) {
/*
A FEN string defines a particular position using only the ASCII character set.
A FEN string contains six fields separated by a space. The fields are:
1) Piece placement (from white's perspective). Each rank is described, starting
with rank 8 and ending with rank 1. Within each rank, the contents of each
square are described from file A through file H. Following the Standard
Algebraic Notation (SAN), each piece is identified by a single letter taken
from the standard English names. White pieces are designated using upper-case
letters ("PNBRQK") whilst Black uses lowercase ("pnbrqk"). Blank squares are
noted using digits 1 through 8 (the number of blank squares), and "/"
separates ranks.
2) Active color. "w" means white moves next, "b" means black.
3) Castling availability. If neither side can castle, this is "-". Otherwise,
this has one or more letters: "K" (White can castle kingside), "Q" (White
can castle queenside), "k" (Black can castle kingside), and/or "q" (Black
can castle queenside).
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.
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
fifty-move rule.
6) Fullmove number. The number of the full move. It starts at 1, and is
incremented after Black's move.
*/
unsigned char col, row, token;
size_t idx;
Square sq = SQ_A8;
std::istringstream ss(fenStr);
clear();
ss >> std::noskipws;
// 1. Piece placement
while ((ss >> token) && !isspace(token))
{
if (isdigit(token))
sq += Square(token - '0'); // Advance the given number of files
else if (token == '/')
sq -= Square(16);
else if ((idx = PieceToChar.find(token)) != string::npos)
{
put_piece(sq, color_of(Piece(idx)), type_of(Piece(idx)));
++sq;
}
}
// 2. Active color
ss >> token;
sideToMove = (token == 'w' ? WHITE : BLACK);
ss >> token;
// 3. Castling availability. Compatible with 3 standards: Normal FEN standard,
// Shredder-FEN that uses the letters of the columns on which the rooks began
// the game instead of KQkq and also X-FEN standard that, in case of Chess960,
// if an inner rook is associated with the castling right, the castling tag is
// replaced by the file letter of the involved rook, as for the Shredder-FEN.
while ((ss >> token) && !isspace(token))
{
Square rsq;
Color c = islower(token) ? BLACK : WHITE;
token = char(toupper(token));
if (token == 'K')
for (rsq = relative_square(c, SQ_H1); type_of(piece_on(rsq)) != ROOK; --rsq) {}
else if (token == 'Q')
for (rsq = relative_square(c, SQ_A1); type_of(piece_on(rsq)) != ROOK; ++rsq) {}
else if (token >= 'A' && token <= 'H')
rsq = make_square(File(token - 'A'), relative_rank(c, RANK_1));
else
continue;
set_castling_right(c, rsq);
}
// 4. En passant square. Ignore if no pawn capture is possible
if ( ((ss >> col) && (col >= 'a' && col <= 'h'))
&& ((ss >> row) && (row == '3' || row == '6')))
{
st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
if (!(attackers_to(st->epSquare) & pieces(sideToMove, PAWN)))
st->epSquare = SQ_NONE;
}
// 5-6. Halfmove clock and fullmove number
ss >> std::skipws >> st->rule50 >> gamePly;
// Convert from fullmove starting from 1 to ply starting from 0,
// handle also common incorrect FEN with fullmove = 0.
gamePly = std::max(2 * (gamePly - 1), 0) + (sideToMove == BLACK);
chess960 = isChess960;
thisThread = th;
set_state(st);
assert(pos_is_ok());
}
/// Position::set_castling_right() is a helper function used to set castling
/// rights given the corresponding color and the rook starting square.
void Position::set_castling_right(Color c, Square rfrom) {
Square kfrom = king_square(c);
CastlingSide cs = kfrom < rfrom ? KING_SIDE : QUEEN_SIDE;
CastlingRight cr = (c | cs);
st->castlingRights |= cr;
castlingRightsMask[kfrom] |= cr;
castlingRightsMask[rfrom] |= cr;
castlingRookSquare[cr] = rfrom;
Square kto = relative_square(c, cs == KING_SIDE ? SQ_G1 : SQ_C1);
Square rto = relative_square(c, cs == KING_SIDE ? SQ_F1 : SQ_D1);
for (Square s = std::min(rfrom, rto); s <= std::max(rfrom, rto); ++s)
if (s != kfrom && s != rfrom)
castlingPath[cr] |= s;
for (Square s = std::min(kfrom, kto); s <= std::max(kfrom, kto); ++s)
if (s != kfrom && s != rfrom)
castlingPath[cr] |= s;
}
/// Position::set_state() computes the hash keys of the position, and other
/// data that once computed is updated incrementally as moves are made.
/// The function is only used when a new position is set up, and to verify
/// the correctness of the StateInfo data when running in debug mode.
void Position::set_state(StateInfo* si) const {
si->key = si->pawnKey = si->materialKey = 0;
si->nonPawnMaterial[WHITE] = si->nonPawnMaterial[BLACK] = VALUE_ZERO;
si->psq = SCORE_ZERO;
si->checkersBB = attackers_to(king_square(sideToMove)) & pieces(~sideToMove);
for (Bitboard b = pieces(); b; )
{
Square s = pop_lsb(&b);
Piece pc = piece_on(s);
si->key ^= Zobrist::psq[color_of(pc)][type_of(pc)][s];
si->psq += psq[color_of(pc)][type_of(pc)][s];
}
if (ep_square() != SQ_NONE)
si->key ^= Zobrist::enpassant[file_of(ep_square())];
if (sideToMove == BLACK)
si->key ^= Zobrist::side;
si->key ^= Zobrist::castling[st->castlingRights];
for (Bitboard b = pieces(PAWN); b; )
{
Square s = pop_lsb(&b);
si->pawnKey ^= Zobrist::psq[color_of(piece_on(s))][PAWN][s];
}
for (Color c = WHITE; c <= BLACK; ++c)
for (PieceType pt = PAWN; pt <= KING; ++pt)
for (int cnt = 0; cnt < pieceCount[c][pt]; ++cnt)
si->materialKey ^= Zobrist::psq[c][pt][cnt];
for (Color c = WHITE; c <= BLACK; ++c)
for (PieceType pt = KNIGHT; pt <= QUEEN; ++pt)
si->nonPawnMaterial[c] += pieceCount[c][pt] * PieceValue[MG][pt];
}
/// Position::fen() returns a FEN representation of the position. In case of
/// Chess960 the Shredder-FEN notation is used. This is mainly a debugging function.
const string Position::fen() const {
int emptyCnt;
std::ostringstream ss;
for (Rank r = RANK_8; r >= RANK_1; --r)
{
for (File f = FILE_A; f <= FILE_H; ++f)
{
for (emptyCnt = 0; f <= FILE_H && empty(make_square(f, r)); ++f)
++emptyCnt;
if (emptyCnt)
ss << emptyCnt;
if (f <= FILE_H)
ss << PieceToChar[piece_on(make_square(f, r))];
}
if (r > RANK_1)
ss << '/';
}
ss << (sideToMove == WHITE ? " w " : " b ");
if (can_castle(WHITE_OO))
ss << (chess960 ? char('A' + file_of(castling_rook_square(WHITE | KING_SIDE))) : 'K');
if (can_castle(WHITE_OOO))
ss << (chess960 ? char('A' + file_of(castling_rook_square(WHITE | QUEEN_SIDE))) : 'Q');
if (can_castle(BLACK_OO))
ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK | KING_SIDE))) : 'k');
if (can_castle(BLACK_OOO))
ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK | QUEEN_SIDE))) : 'q');
if (!can_castle(WHITE) && !can_castle(BLACK))
ss << '-';
ss << (ep_square() == SQ_NONE ? " - " : " " + UCI::square(ep_square()) + " ")
<< st->rule50 << " " << 1 + (gamePly - (sideToMove == BLACK)) / 2;
return ss.str();
}
/// Position::game_phase() calculates the game phase interpolating total non-pawn
/// material between endgame and midgame limits.
Phase Position::game_phase() const {
Value npm = st->nonPawnMaterial[WHITE] + st->nonPawnMaterial[BLACK];
npm = std::max(EndgameLimit, std::min(npm, MidgameLimit));
return Phase(((npm - EndgameLimit) * PHASE_MIDGAME) / (MidgameLimit - EndgameLimit));
}
/// Position::check_blockers() returns a bitboard of all the pieces with color
/// 'c' that are blocking check on the king with color 'kingColor'. A piece
/// blocks a check if removing that piece from the board would result in a
/// position where the king is in check. A check blocking piece can be either a
/// pinned or a discovered check piece, according if its color 'c' is the same
/// or the opposite of 'kingColor'.
Bitboard Position::check_blockers(Color c, Color kingColor) const {
Bitboard b, pinners, result = 0;
Square ksq = king_square(kingColor);
// Pinners are sliders that give check when a pinned piece is removed
pinners = ( (pieces( ROOK, QUEEN) & PseudoAttacks[ROOK ][ksq])
| (pieces(BISHOP, QUEEN) & PseudoAttacks[BISHOP][ksq])) & pieces(~kingColor);
while (pinners)
{
b = between_bb(ksq, pop_lsb(&pinners)) & pieces();
if (!more_than_one(b))
result |= b & pieces(c);
}
return result;
}
/// Position::attackers_to() computes a bitboard of all pieces which attack a
/// given square. Slider attacks use the occupied bitboard to indicate occupancy.
Bitboard Position::attackers_to(Square s, Bitboard occupied) const {
return (attacks_from<PAWN>(s, BLACK) & pieces(WHITE, PAWN))
| (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))
| (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
| (attacks_bb<ROOK>(s, occupied) & pieces(ROOK, QUEEN))
| (attacks_bb<BISHOP>(s, occupied) & pieces(BISHOP, QUEEN))
| (attacks_from<KING>(s) & pieces(KING));
}
/// Position::legal() tests whether a pseudo-legal move is legal
bool Position::legal(Move m, Bitboard pinned) const {
assert(is_ok(m));
assert(pinned == pinned_pieces(sideToMove));
Color us = sideToMove;
Square from = from_sq(m);
assert(color_of(moved_piece(m)) == us);
assert(piece_on(king_square(us)) == make_piece(us, KING));
// En passant captures are a tricky special case. Because they are rather
// uncommon, we do it simply by testing whether the king is attacked after
// the move is made.
if (type_of(m) == ENPASSANT)
{
Square ksq = king_square(us);
Square to = to_sq(m);
Square capsq = to - pawn_push(us);
Bitboard occupied = (pieces() ^ from ^ capsq) | to;
assert(to == ep_square());
assert(moved_piece(m) == make_piece(us, PAWN));
assert(piece_on(capsq) == make_piece(~us, PAWN));
assert(piece_on(to) == NO_PIECE);
return !(attacks_bb< ROOK>(ksq, occupied) & pieces(~us, QUEEN, ROOK))
&& !(attacks_bb<BISHOP>(ksq, occupied) & pieces(~us, QUEEN, BISHOP));
}
// If the moving piece is a king, check whether the destination
// square is attacked by the opponent. Castling moves are checked
// for legality during move generation.
if (type_of(piece_on(from)) == KING)
return type_of(m) == CASTLING || !(attackers_to(to_sq(m)) & pieces(~us));
// A non-king move is legal if and only if it is not pinned or it
// is moving along the ray towards or away from the king.
return !pinned
|| !(pinned & from)
|| aligned(from, to_sq(m), king_square(us));
}
/// Position::pseudo_legal() takes a random move and tests whether the move is
/// pseudo legal. It is used to validate moves from TT that can be corrupted
/// due to SMP concurrent access or hash position key aliasing.
bool Position::pseudo_legal(const Move m) const {
Color us = sideToMove;
Square from = from_sq(m);
Square to = to_sq(m);
Piece pc = moved_piece(m);
// Use a slower but simpler function for uncommon cases
if (type_of(m) != NORMAL)
return MoveList<LEGAL>(*this).contains(m);
// Is not a promotion, so promotion piece must be empty
if (promotion_type(m) - 2 != NO_PIECE_TYPE)
return false;
// If the 'from' square is not occupied by a piece belonging to the side to
// move, the move is obviously not legal.
if (pc == NO_PIECE || color_of(pc) != us)
return false;
// The destination square cannot be occupied by a friendly piece
if (pieces(us) & to)
return false;
// Handle the special case of a pawn move
if (type_of(pc) == PAWN)
{
// We have already handled promotion moves, so destination
// cannot be on the 8th/1st rank.
if (rank_of(to) == relative_rank(us, RANK_8))
return false;
if ( !(attacks_from<PAWN>(from, us) & pieces(~us) & to) // Not a capture
&& !((from + pawn_push(us) == to) && empty(to)) // Not a single push
&& !( (from + 2 * pawn_push(us) == to) // Not a double push
&& (rank_of(from) == relative_rank(us, RANK_2))
&& empty(to)
&& empty(to - pawn_push(us))))
return false;
}
else if (!(attacks_from(pc, from) & to))
return false;
// Evasions generator already takes care to avoid some kind of illegal moves
// and legal() relies on this. We therefore have to take care that the same
// kind of moves are filtered out here.
if (checkers())
{
if (type_of(pc) != KING)
{
// Double check? In this case a king move is required
if (more_than_one(checkers()))
return false;
// Our move must be a blocking evasion or a capture of the checking piece
if (!((between_bb(lsb(checkers()), king_square(us)) | checkers()) & to))
return false;
}
// In case of king moves under check we have to remove king so as to catch
// invalid moves like b1a1 when opposite queen is on c1.
else if (attackers_to(to, pieces() ^ from) & pieces(~us))
return false;
}
return true;
}
/// Position::gives_check() tests whether a pseudo-legal move gives a check
bool Position::gives_check(Move m, const CheckInfo& ci) const {
assert(is_ok(m));
assert(ci.dcCandidates == discovered_check_candidates());
assert(color_of(moved_piece(m)) == sideToMove);
Square from = from_sq(m);
Square to = to_sq(m);
PieceType pt = type_of(piece_on(from));
// Is there a direct check?
if (ci.checkSq[pt] & to)
return true;
// Is there a discovered check?
if ( unlikely(ci.dcCandidates)
&& (ci.dcCandidates & from)
&& !aligned(from, to, ci.ksq))
return true;
switch (type_of(m))
{
case NORMAL:
return false;
case PROMOTION:
return attacks_bb(Piece(promotion_type(m)), to, pieces() ^ from) & ci.ksq;
// En passant capture with check? We have already handled the case
// of direct checks and ordinary discovered check, so the only case we
// need to handle is the unusual case of a discovered check through
// the captured pawn.
case ENPASSANT:
{
Square capsq = make_square(file_of(to), rank_of(from));
Bitboard b = (pieces() ^ from ^ capsq) | to;
return (attacks_bb< ROOK>(ci.ksq, b) & pieces(sideToMove, QUEEN, ROOK))
| (attacks_bb<BISHOP>(ci.ksq, b) & pieces(sideToMove, QUEEN, BISHOP));
}
case CASTLING:
{
Square kfrom = from;
Square rfrom = to; // Castling is encoded as 'King captures the rook'
Square kto = relative_square(sideToMove, rfrom > kfrom ? SQ_G1 : SQ_C1);
Square rto = relative_square(sideToMove, rfrom > kfrom ? SQ_F1 : SQ_D1);
return (PseudoAttacks[ROOK][rto] & ci.ksq)
&& (attacks_bb<ROOK>(rto, (pieces() ^ kfrom ^ rfrom) | rto | kto) & ci.ksq);
}
default:
assert(false);
return false;
}
}
/// Position::do_move() makes a move, and saves all information necessary
/// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
/// moves should be filtered out before this function is called.
void Position::do_move(Move m, StateInfo& newSt) {
CheckInfo ci(*this);
do_move(m, newSt, ci, gives_check(m, ci));
}
void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
assert(is_ok(m));
assert(&newSt != st);
++nodes;
Key k = st->key;
// Copy some fields of the old state to our new StateInfo object except the
// ones which are going to be recalculated from scratch anyway and then switch
// our state pointer to point to the new (ready to be updated) state.
std::memcpy(&newSt, st, StateCopySize64 * sizeof(uint64_t));
newSt.previous = st;
st = &newSt;
// Update side to move
k ^= Zobrist::side;
// Increment ply counters. In particular, rule50 will be reset to zero later on
// in case of a capture or a pawn move.
++gamePly;
++st->rule50;
++st->pliesFromNull;
Color us = sideToMove;
Color them = ~us;
Square from = from_sq(m);
Square to = to_sq(m);
Piece pc = piece_on(from);
PieceType pt = type_of(pc);
PieceType captured = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));
assert(color_of(pc) == us);
assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them || type_of(m) == CASTLING);
assert(captured != KING);
if (type_of(m) == CASTLING)
{
assert(pc == make_piece(us, KING));
Square rfrom, rto;
do_castling<true>(from, to, rfrom, rto);
captured = NO_PIECE_TYPE;
st->psq += psq[us][ROOK][rto] - psq[us][ROOK][rfrom];
k ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
}
if (captured)
{
Square capsq = to;
// If the captured piece is a pawn, update pawn hash key, otherwise
// update non-pawn material.
if (captured == PAWN)
{
if (type_of(m) == ENPASSANT)
{
capsq += pawn_push(them);
assert(pt == PAWN);
assert(to == st->epSquare);
assert(relative_rank(us, to) == RANK_6);
assert(piece_on(to) == NO_PIECE);
assert(piece_on(capsq) == make_piece(them, PAWN));
board[capsq] = NO_PIECE;
}
st->pawnKey ^= Zobrist::psq[them][PAWN][capsq];
}
else
st->nonPawnMaterial[them] -= PieceValue[MG][captured];
// Update board and piece lists
remove_piece(capsq, them, captured);
// Update material hash key and prefetch access to materialTable
k ^= Zobrist::psq[them][captured][capsq];
st->materialKey ^= Zobrist::psq[them][captured][pieceCount[them][captured]];
prefetch((char*)thisThread->materialTable[st->materialKey]);
// Update incremental scores
st->psq -= psq[them][captured][capsq];
// Reset rule 50 counter
st->rule50 = 0;
}
// Update hash key
k ^= Zobrist::psq[us][pt][from] ^ Zobrist::psq[us][pt][to];
// Reset en passant square
if (st->epSquare != SQ_NONE)
{
k ^= Zobrist::enpassant[file_of(st->epSquare)];
st->epSquare = SQ_NONE;
}
// Update castling rights if needed
if (st->castlingRights && (castlingRightsMask[from] | castlingRightsMask[to]))
{
int cr = castlingRightsMask[from] | castlingRightsMask[to];
k ^= Zobrist::castling[st->castlingRights & cr];
st->castlingRights &= ~cr;
}
// Move the piece. The tricky Chess960 castling is handled earlier
if (type_of(m) != CASTLING)
move_piece(from, to, us, pt);
// If the moving piece is a pawn do some special extra work
if (pt == PAWN)
{
// Set en-passant square if the moved pawn can be captured
if ( (int(to) ^ int(from)) == 16
&& (attacks_from<PAWN>(from + pawn_push(us), us) & pieces(them, PAWN)))
{
st->epSquare = Square((from + to) / 2);
k ^= Zobrist::enpassant[file_of(st->epSquare)];
}
else if (type_of(m) == PROMOTION)
{
PieceType promotion = promotion_type(m);
assert(relative_rank(us, to) == RANK_8);
assert(promotion >= KNIGHT && promotion <= QUEEN);
remove_piece(to, us, PAWN);
put_piece(to, us, promotion);
// Update hash keys
k ^= Zobrist::psq[us][PAWN][to] ^ Zobrist::psq[us][promotion][to];
st->pawnKey ^= Zobrist::psq[us][PAWN][to];
st->materialKey ^= Zobrist::psq[us][promotion][pieceCount[us][promotion]-1]
^ Zobrist::psq[us][PAWN][pieceCount[us][PAWN]];
// Update incremental score
st->psq += psq[us][promotion][to] - psq[us][PAWN][to];
// Update material
st->nonPawnMaterial[us] += PieceValue[MG][promotion];
}
// Update pawn hash key and prefetch access to pawnsTable
st->pawnKey ^= Zobrist::psq[us][PAWN][from] ^ Zobrist::psq[us][PAWN][to];
prefetch((char*)thisThread->pawnsTable[st->pawnKey]);
// Reset rule 50 draw counter
st->rule50 = 0;
}
// Update incremental scores
st->psq += psq[us][pt][to] - psq[us][pt][from];
// Set capture piece
st->capturedType = captured;
// Update the key with the final value
st->key = k;
// Update checkers bitboard: piece must be already moved due to attacks_from()
st->checkersBB = 0;
if (moveIsCheck)
{
if (type_of(m) != NORMAL)
st->checkersBB = attackers_to(king_square(them)) & pieces(us);
else
{
// Direct checks
if (ci.checkSq[pt] & to)
st->checkersBB |= to;
// Discovered checks
if (unlikely(ci.dcCandidates) && (ci.dcCandidates & from))
{
if (pt != ROOK)
st->checkersBB |= attacks_from<ROOK>(king_square(them)) & pieces(us, QUEEN, ROOK);
if (pt != BISHOP)
st->checkersBB |= attacks_from<BISHOP>(king_square(them)) & pieces(us, QUEEN, BISHOP);
}
}
}
sideToMove = ~sideToMove;
assert(pos_is_ok());
}
/// Position::undo_move() unmakes a move. When it returns, the position should
/// be restored to exactly the same state as before the move was made.
void Position::undo_move(Move m) {
assert(is_ok(m));
sideToMove = ~sideToMove;
Color us = sideToMove;
Square from = from_sq(m);
Square to = to_sq(m);
PieceType pt = type_of(piece_on(to));
assert(empty(from) || type_of(m) == CASTLING);
assert(st->capturedType != KING);
if (type_of(m) == PROMOTION)
{
assert(pt == promotion_type(m));
assert(relative_rank(us, to) == RANK_8);
assert(promotion_type(m) >= KNIGHT && promotion_type(m) <= QUEEN);
remove_piece(to, us, promotion_type(m));
put_piece(to, us, PAWN);
pt = PAWN;
}
if (type_of(m) == CASTLING)
{
Square rfrom, rto;
do_castling<false>(from, to, rfrom, rto);
}
else
{
move_piece(to, from, us, pt); // Put the piece back at the source square
if (st->capturedType)
{
Square capsq = to;
if (type_of(m) == ENPASSANT)
{
capsq -= pawn_push(us);
assert(pt == PAWN);
assert(to == st->previous->epSquare);
assert(relative_rank(us, to) == RANK_6);
assert(piece_on(capsq) == NO_PIECE);
}
put_piece(capsq, ~us, st->capturedType); // Restore the captured piece
}
}
// Finally point our state pointer back to the previous state
st = st->previous;
--gamePly;
assert(pos_is_ok());
}
/// Position::do_castling() is a helper used to do/undo a castling move. This
/// is a bit tricky, especially in Chess960.
template<bool Do>
void Position::do_castling(Square from, Square& to, Square& rfrom, Square& rto) {
bool kingSide = to > from;
rfrom = to; // Castling is encoded as "king captures friendly rook"
rto = relative_square(sideToMove, kingSide ? SQ_F1 : SQ_D1);
to = relative_square(sideToMove, kingSide ? SQ_G1 : SQ_C1);
// Remove both pieces first since squares could overlap in Chess960
remove_piece(Do ? from : to, sideToMove, KING);
remove_piece(Do ? rfrom : rto, sideToMove, ROOK);
board[Do ? from : to] = board[Do ? rfrom : rto] = NO_PIECE; // Since remove_piece doesn't do it for us
put_piece(Do ? to : from, sideToMove, KING);
put_piece(Do ? rto : rfrom, sideToMove, ROOK);
}
/// Position::do(undo)_null_move() is used to do(undo) a "null move": It flips
/// the side to move without executing any move on the board.
void Position::do_null_move(StateInfo& newSt) {
assert(!checkers());
std::memcpy(&newSt, st, sizeof(StateInfo)); // Fully copy here
newSt.previous = st;
st = &newSt;
if (st->epSquare != SQ_NONE)
{
st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
st->epSquare = SQ_NONE;
}
st->key ^= Zobrist::side;
prefetch((char*)TT.first_entry(st->key));
++st->rule50;
st->pliesFromNull = 0;
sideToMove = ~sideToMove;
assert(pos_is_ok());
}