1/*
2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
6
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
11
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
19*/
20
21#include <algorithm>
22#include <cassert>
23#include <cstring> // For std::memset
24#include <iomanip>
25#include <sstream>
26
27#include "bitboard.h"
28#include "evaluate.h"
29#include "material.h"
30#include "pawns.h"
31#include "thread.h"
32
33namespace Trace {
34
35 enum Tracing { NO_TRACE, TRACE };
36
37 enum Term { // The first 8 entries are reserved for PieceType
38 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
39 };
40
41 Score scores[TERM_NB][COLOR_NB];
42
43 double to_cp(Value v) { return double(v) / PawnValueEg; }
44
45 void add(int idx, Color c, Score s) {
46 scores[idx][c] = s;
47 }
48
49 void add(int idx, Score w, Score b = SCORE_ZERO) {
50 scores[idx][WHITE] = w;
51 scores[idx][BLACK] = b;
52 }
53
54 std::ostream& operator<<(std::ostream& os, Score s) {
55 os << std::setw(5) << to_cp(mg_value(s)) << " "
56 << std::setw(5) << to_cp(eg_value(s));
57 return os;
58 }
59
60 std::ostream& operator<<(std::ostream& os, Term t) {
61
62 if (t == MATERIAL || t == IMBALANCE || t == INITIATIVE || t == TOTAL)
63 os << " ---- ----" << " | " << " ---- ----";
64 else
65 os << scores[t][WHITE] << " | " << scores[t][BLACK];
66
67 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
68 return os;
69 }
70}
71
72using namespace Trace;
73
74namespace {
75
76 // Threshold for lazy and space evaluation
77 constexpr Value LazyThreshold = Value(1400);
78 constexpr Value SpaceThreshold = Value(12222);
79
80 // KingAttackWeights[PieceType] contains king attack weights by piece type
81 constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 77, 55, 44, 10 };
82
83 // Penalties for enemy's safe checks
84 constexpr int QueenSafeCheck = 780;
85 constexpr int RookSafeCheck = 1080;
86 constexpr int BishopSafeCheck = 635;
87 constexpr int KnightSafeCheck = 790;
88
89#define S(mg, eg) make_score(mg, eg)
90
91 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
92 // indexed by piece type and number of attacked squares in the mobility area.
93 constexpr Score MobilityBonus[][32] = {
94 { S(-62,-81), S(-53,-56), S(-12,-30), S( -4,-14), S( 3, 8), S( 13, 15), // Knights
95 S( 22, 23), S( 28, 27), S( 33, 33) },
96 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
97 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
98 S( 91, 88), S( 98, 97) },
99 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
100 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
101 S( 46,166), S( 48,169), S( 58,171) },
102 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
103 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
104 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
105 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
106 S(106,184), S(109,191), S(113,206), S(116,212) }
107 };
108
109 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
110 // no (friendly) pawn on the rook file.
111 constexpr Score RookOnFile[] = { S(18, 7), S(44, 20) };
112
113 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
114 // which piece type attacks which one. Attacks on lesser pieces which are
115 // pawn-defended are not considered.
116 constexpr Score ThreatByMinor[PIECE_TYPE_NB] = {
117 S(0, 0), S(0, 31), S(39, 42), S(57, 44), S(68, 112), S(62, 120)
118 };
119
120 constexpr Score ThreatByRook[PIECE_TYPE_NB] = {
121 S(0, 0), S(0, 24), S(38, 71), S(38, 61), S(0, 38), S(51, 38)
122 };
123
124 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
125 constexpr Score PassedRank[RANK_NB] = {
126 S(0, 0), S(10, 28), S(17, 33), S(15, 41), S(62, 72), S(168, 177), S(276, 260)
127 };
128
129 // Assorted bonuses and penalties
130 constexpr Score BishopPawns = S( 3, 7);
131 constexpr Score CorneredBishop = S( 50, 50);
132 constexpr Score FlankAttacks = S( 8, 0);
133 constexpr Score Hanging = S( 69, 36);
134 constexpr Score KingProtector = S( 7, 8);
135 constexpr Score KnightOnQueen = S( 16, 12);
136 constexpr Score LongDiagonalBishop = S( 45, 0);
137 constexpr Score MinorBehindPawn = S( 18, 3);
138 constexpr Score Outpost = S( 18, 6);
139 constexpr Score PassedFile = S( 11, 8);
140 constexpr Score PawnlessFlank = S( 17, 95);
141 constexpr Score RestrictedPiece = S( 7, 7);
142 constexpr Score RookOnPawn = S( 10, 32);
143 constexpr Score SliderOnQueen = S( 59, 18);
144 constexpr Score ThreatByKing = S( 24, 89);
145 constexpr Score ThreatByPawnPush = S( 48, 39);
146 constexpr Score ThreatByRank = S( 13, 0);
147 constexpr Score ThreatBySafePawn = S(173, 94);
148 constexpr Score TrappedRook = S( 47, 4);
149 constexpr Score WeakQueen = S( 49, 15);
150
151#undef S
152
153 // Evaluation class computes and stores attacks tables and other working data
154 template<Tracing T>
155 class Evaluation {
156
157 public:
158 Evaluation() = delete;
159 explicit Evaluation(const Position& p) : pos(p) {}
160 Evaluation& operator=(const Evaluation&) = delete;
161 Value value();
162
163 private:
164 template<Color Us> void initialize();
165 template<Color Us, PieceType Pt> Score pieces();
166 template<Color Us> Score king() const;
167 template<Color Us> Score threats() const;
168 template<Color Us> Score passed() const;
169 template<Color Us> Score space() const;
170 ScaleFactor scale_factor(Value eg) const;
171 Score initiative(Value eg) const;
172
173 const Position& pos;
174 Material::Entry* me;
175 Pawns::Entry* pe;
176 Bitboard mobilityArea[COLOR_NB];
177 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
178
179 // attackedBy[color][piece type] is a bitboard representing all squares
180 // attacked by a given color and piece type. Special "piece types" which
181 // is also calculated is ALL_PIECES.
182 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
183
184 // attackedBy2[color] are the squares attacked by at least 2 units of a given
185 // color, including x-rays. But diagonal x-rays through pawns are not computed.
186 Bitboard attackedBy2[COLOR_NB];
187
188 // kingRing[color] are the squares adjacent to the king plus some other
189 // very near squares, depending on king position.
190 Bitboard kingRing[COLOR_NB];
191
192 // kingAttackersCount[color] is the number of pieces of the given color
193 // which attack a square in the kingRing of the enemy king.
194 int kingAttackersCount[COLOR_NB];
195
196 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of
197 // the given color which attack a square in the kingRing of the enemy king.
198 // The weights of the individual piece types are given by the elements in
199 // the KingAttackWeights array.
200 int kingAttackersWeight[COLOR_NB];
201
202 // kingAttacksCount[color] is the number of attacks by the given color to
203 // squares directly adjacent to the enemy king. Pieces which attack more
204 // than one square are counted multiple times. For instance, if there is
205 // a white knight on g5 and black's king is on g8, this white knight adds 2
206 // to kingAttacksCount[WHITE].
207 int kingAttacksCount[COLOR_NB];
208 };
209
210
211 // Evaluation::initialize() computes king and pawn attacks, and the king ring
212 // bitboard for a given color. This is done at the beginning of the evaluation.
213 template<Tracing T> template<Color Us>
214 void Evaluation<T>::initialize() {
215
216 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
217 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
218 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
219 constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
220
221 const Square ksq = pos.square<KING>(Us);
222
223 Bitboard dblAttackByPawn = pawn_double_attacks_bb<Us>(pos.pieces(Us, PAWN));
224
225 // Find our pawns that are blocked or on the first two ranks
226 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
227
228 // Squares occupied by those pawns, by our king or queen or controlled by
229 // enemy pawns are excluded from the mobility area.
230 mobilityArea[Us] = ~(b | pos.pieces(Us, KING, QUEEN) | pe->pawn_attacks(Them));
231
232 // Initialize attackedBy[] for king and pawns
233 attackedBy[Us][KING] = pos.attacks_from<KING>(ksq);
234 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
235 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
236 attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
237
238 // Init our king safety tables
239 kingRing[Us] = attackedBy[Us][KING];
240 if (relative_rank(Us, ksq) == RANK_1)
241 kingRing[Us] |= shift<Up>(kingRing[Us]);
242
243 if (file_of(ksq) == FILE_H)
244 kingRing[Us] |= shift<WEST>(kingRing[Us]);
245
246 else if (file_of(ksq) == FILE_A)
247 kingRing[Us] |= shift<EAST>(kingRing[Us]);
248
249 kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
250 kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
251
252 // Remove from kingRing[] the squares defended by two pawns
253 kingRing[Us] &= ~dblAttackByPawn;
254 }
255
256
257 // Evaluation::pieces() scores pieces of a given color and type
258 template<Tracing T> template<Color Us, PieceType Pt>
259 Score Evaluation<T>::pieces() {
260
261 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
262 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
263 constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
264 : Rank5BB | Rank4BB | Rank3BB);
265 const Square* pl = pos.squares<Pt>(Us);
266
267 Bitboard b, bb;
268 Score score = SCORE_ZERO;
269
270 attackedBy[Us][Pt] = 0;
271
272 for (Square s = *pl; s != SQ_NONE; s = *++pl)
273 {
274 // Find attacked squares, including x-ray attacks for bishops and rooks
275 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
276 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
277 : pos.attacks_from<Pt>(s);
278
279 if (pos.blockers_for_king(Us) & s)
280 b &= LineBB[pos.square<KING>(Us)][s];
281
282 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
283 attackedBy[Us][Pt] |= b;
284 attackedBy[Us][ALL_PIECES] |= b;
285
286 if (b & kingRing[Them])
287 {
288 kingAttackersCount[Us]++;
289 kingAttackersWeight[Us] += KingAttackWeights[Pt];
290 kingAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
291 }
292
293 int mob = popcount(b & mobilityArea[Us]);
294
295 mobility[Us] += MobilityBonus[Pt - 2][mob];
296
297 if (Pt == BISHOP || Pt == KNIGHT)
298 {
299 // Bonus if piece is on an outpost square or can reach one
300 bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
301 if (bb & s)
302 score += Outpost * (Pt == KNIGHT ? 4 : 2);
303
304 else if (bb & b & ~pos.pieces(Us))
305 score += Outpost * (Pt == KNIGHT ? 2 : 1);
306
307 // Knight and Bishop bonus for being right behind a pawn
308 if (shift<Down>(pos.pieces(PAWN)) & s)
309 score += MinorBehindPawn;
310
311 // Penalty if the piece is far from the king
312 score -= KingProtector * distance(s, pos.square<KING>(Us));
313
314 if (Pt == BISHOP)
315 {
316 // Penalty according to number of pawns on the same color square as the
317 // bishop, bigger when the center files are blocked with pawns.
318 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
319
320 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
321 * (1 + popcount(blocked & CenterFiles));
322
323 // Bonus for bishop on a long diagonal which can "see" both center squares
324 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
325 score += LongDiagonalBishop;
326 }
327
328 // An important Chess960 pattern: A cornered bishop blocked by a friendly
329 // pawn diagonally in front of it is a very serious problem, especially
330 // when that pawn is also blocked.
331 if ( Pt == BISHOP
332 && pos.is_chess960()
333 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
334 {
335 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
336 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
337 score -= !pos.empty(s + d + pawn_push(Us)) ? CorneredBishop * 4
338 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? CorneredBishop * 2
339 : CorneredBishop;
340 }
341 }
342
343 if (Pt == ROOK)
344 {
345 // Bonus for aligning rook with enemy pawns on the same rank/file
346 if (relative_rank(Us, s) >= RANK_5)
347 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
348
349 // Bonus for rook on an open or semi-open file
350 if (pos.is_on_semiopen_file(Us, s))
351 score += RookOnFile[bool(pos.is_on_semiopen_file(Them, s))];
352
353 // Penalty when trapped by the king, even more if the king cannot castle
354 else if (mob <= 3)
355 {
356 File kf = file_of(pos.square<KING>(Us));
357 if ((kf < FILE_E) == (file_of(s) < kf))
358 score -= TrappedRook * (1 + !pos.castling_rights(Us));
359 }
360 }
361
362 if (Pt == QUEEN)
363 {
364 // Penalty if any relative pin or discovered attack against the queen
365 Bitboard queenPinners;
366 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
367 score -= WeakQueen;
368 }
369 }
370 if (T)
371 Trace::add(Pt, Us, score);
372
373 return score;
374 }
375
376
377 // Evaluation::king() assigns bonuses and penalties to a king of a given color
378 template<Tracing T> template<Color Us>
379 Score Evaluation<T>::king() const {
380
381 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
382 constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
383 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
384
385 Bitboard weak, b1, b2, safe, unsafeChecks = 0;
386 Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
387 int kingDanger = 0;
388 const Square ksq = pos.square<KING>(Us);
389
390 // Init the score with king shelter and enemy pawns storm
391 Score score = pe->king_safety<Us>(pos);
392
393 // Attacked squares defended at most once by our queen or king
394 weak = attackedBy[Them][ALL_PIECES]
395 & ~attackedBy2[Us]
396 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
397
398 // Analyse the safe enemy's checks which are possible on next move
399 safe = ~pos.pieces(Them);
400 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
401
402 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
403 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
404
405 // Enemy rooks checks
406 rookChecks = b1 & safe & attackedBy[Them][ROOK];
407
408 if (rookChecks)
409 kingDanger += RookSafeCheck;
410 else
411 unsafeChecks |= b1 & attackedBy[Them][ROOK];
412
413 // Enemy queen safe checks: we count them only if they are from squares from
414 // which we can't give a rook check, because rook checks are more valuable.
415 queenChecks = (b1 | b2)
416 & attackedBy[Them][QUEEN]
417 & safe
418 & ~attackedBy[Us][QUEEN]
419 & ~rookChecks;
420
421 if (queenChecks)
422 kingDanger += QueenSafeCheck;
423
424 // Enemy bishops checks: we count them only if they are from squares from
425 // which we can't give a queen check, because queen checks are more valuable.
426 bishopChecks = b2
427 & attackedBy[Them][BISHOP]
428 & safe
429 & ~queenChecks;
430
431 if (bishopChecks)
432 kingDanger += BishopSafeCheck;
433 else
434 unsafeChecks |= b2 & attackedBy[Them][BISHOP];
435
436 // Enemy knights checks
437 knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
438
439 if (knightChecks & safe)
440 kingDanger += KnightSafeCheck;
441 else
442 unsafeChecks |= knightChecks;
443
444 // Find the squares that opponent attacks in our king flank, and the squares
445 // which are attacked twice in that flank.
446 b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
447 b2 = b1 & attackedBy2[Them];
448
449 int kingFlankAttacks = popcount(b1) + popcount(b2);
450
451 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
452 + 69 * kingAttacksCount[Them]
453 + 185 * popcount(kingRing[Us] & weak)
454 - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
455 - 35 * bool(attackedBy[Us][BISHOP] & attackedBy[Us][KING])
456 + 148 * popcount(unsafeChecks)
457 + 98 * popcount(pos.blockers_for_king(Us))
458 - 873 * !pos.count<QUEEN>(Them)
459 - 6 * mg_value(score) / 8
460 + mg_value(mobility[Them] - mobility[Us])
461 + 5 * kingFlankAttacks * kingFlankAttacks / 16
462 - 7;
463
464 // Transform the kingDanger units into a Score, and subtract it from the evaluation
465 if (kingDanger > 100)
466 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
467
468 // Penalty when our king is on a pawnless flank
469 if (!(pos.pieces(PAWN) & KingFlank[file_of(ksq)]))
470 score -= PawnlessFlank;
471
472 // Penalty if king flank is under attack, potentially moving toward the king
473 score -= FlankAttacks * kingFlankAttacks;
474
475 if (T)
476 Trace::add(KING, Us, score);
477
478 return score;
479 }
480
481
482 // Evaluation::threats() assigns bonuses according to the types of the
483 // attacking and the attacked pieces.
484 template<Tracing T> template<Color Us>
485 Score Evaluation<T>::threats() const {
486
487 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
488 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
489 constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
490
491 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safe;
492 Score score = SCORE_ZERO;
493
494 // Non-pawn enemies
495 nonPawnEnemies = pos.pieces(Them) & ~pos.pieces(PAWN);
496
497 // Squares strongly protected by the enemy, either because they defend the
498 // square with a pawn, or because they defend the square twice and we don't.
499 stronglyProtected = attackedBy[Them][PAWN]
500 | (attackedBy2[Them] & ~attackedBy2[Us]);
501
502 // Non-pawn enemies, strongly protected
503 defended = nonPawnEnemies & stronglyProtected;
504
505 // Enemies not strongly protected and under our attack
506 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
507
508 // Bonus according to the kind of attacking pieces
509 if (defended | weak)
510 {
511 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
512 while (b)
513 {
514 Square s = pop_lsb(&b);
515 score += ThreatByMinor[type_of(pos.piece_on(s))];
516 if (type_of(pos.piece_on(s)) != PAWN)
517 score += ThreatByRank * (int)relative_rank(Them, s);
518 }
519
520 b = weak & attackedBy[Us][ROOK];
521 while (b)
522 {
523 Square s = pop_lsb(&b);
524 score += ThreatByRook[type_of(pos.piece_on(s))];
525 if (type_of(pos.piece_on(s)) != PAWN)
526 score += ThreatByRank * (int)relative_rank(Them, s);
527 }
528
529 if (weak & attackedBy[Us][KING])
530 score += ThreatByKing;
531
532 b = ~attackedBy[Them][ALL_PIECES]
533 | (nonPawnEnemies & attackedBy2[Us]);
534 score += Hanging * popcount(weak & b);
535 }
536
537 // Bonus for restricting their piece moves
538 b = attackedBy[Them][ALL_PIECES]
539 & ~stronglyProtected
540 & attackedBy[Us][ALL_PIECES];
541
542 score += RestrictedPiece * popcount(b);
543
544 // Protected or unattacked squares
545 safe = ~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES];
546
547 // Bonus for attacking enemy pieces with our relatively safe pawns
548 b = pos.pieces(Us, PAWN) & safe;
549 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
550 score += ThreatBySafePawn * popcount(b);
551
552 // Find squares where our pawns can push on the next move
553 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
554 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
555
556 // Keep only the squares which are relatively safe
557 b &= ~attackedBy[Them][PAWN] & safe;
558
559 // Bonus for safe pawn threats on the next move
560 b = pawn_attacks_bb<Us>(b) & nonPawnEnemies;
561 score += ThreatByPawnPush * popcount(b);
562
563 // Bonus for threats on the next moves against enemy queen
564 if (pos.count<QUEEN>(Them) == 1)
565 {
566 Square s = pos.square<QUEEN>(Them);
567 safe = mobilityArea[Us] & ~stronglyProtected;
568
569 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
570
571 score += KnightOnQueen * popcount(b & safe);
572
573 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
574 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
575
576 score += SliderOnQueen * popcount(b & safe & attackedBy2[Us]);
577 }
578
579 if (T)
580 Trace::add(THREAT, Us, score);
581
582 return score;
583 }
584
585 // Evaluation::passed() evaluates the passed pawns and candidate passed
586 // pawns of the given color.
587
588 template<Tracing T> template<Color Us>
589 Score Evaluation<T>::passed() const {
590
591 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
592 constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
593
594 auto king_proximity = [&](Color c, Square s) {
595 return std::min(distance(pos.square<KING>(c), s), 5);
596 };
597
598 Bitboard b, bb, squaresToQueen, unsafeSquares;
599 Score score = SCORE_ZERO;
600
601 b = pe->passed_pawns(Us);
602
603 while (b)
604 {
605 Square s = pop_lsb(&b);
606
607 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
608
609 int r = relative_rank(Us, s);
610 File f = file_of(s);
611
612 Score bonus = PassedRank[r];
613
614 if (r > RANK_3)
615 {
616 int w = 5 * r - 13;
617 Square blockSq = s + Up;
618
619 // Adjust bonus based on the king's proximity
620 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
621 - king_proximity(Us, blockSq) * 2) * w);
622
623 // If blockSq is not the queening square then consider also a second push
624 if (r != RANK_7)
625 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
626
627 // If the pawn is free to advance, then increase the bonus
628 if (pos.empty(blockSq))
629 {
630 squaresToQueen = forward_file_bb(Us, s);
631 unsafeSquares = passed_pawn_span(Us, s);
632
633 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
634
635 if (!(pos.pieces(Them) & bb))
636 unsafeSquares &= attackedBy[Them][ALL_PIECES];
637
638 // If there are no enemy attacks on passed pawn span, assign a big bonus.
639 // Otherwise assign a smaller bonus if the path to queen is not attacked
640 // and even smaller bonus if it is attacked but block square is not.
641 int k = !unsafeSquares ? 35 :
642 !(unsafeSquares & squaresToQueen) ? 20 :
643 !(unsafeSquares & blockSq) ? 9 :
644 0 ;
645
646 // Assign a larger bonus if the block square is defended
647 if ((pos.pieces(Us) & bb) || (attackedBy[Us][ALL_PIECES] & blockSq))
648 k += 5;
649
650 bonus += make_score(k * w, k * w);
651 }
652 } // r > RANK_3
653
654 // Scale down bonus for candidate passers which need more than one
655 // pawn push to become passed, or have a pawn in front of them.
656 if ( !pos.pawn_passed(Us, s + Up)
657 || (pos.pieces(PAWN) & (s + Up)))
658 bonus = bonus / 2;
659
660 score += bonus - PassedFile * std::min(f, ~f);
661 }
662
663 if (T)
664 Trace::add(PASSED, Us, score);
665
666 return score;
667 }
668
669
670 // Evaluation::space() computes the space evaluation for a given side. The
671 // space evaluation is a simple bonus based on the number of safe squares
672 // available for minor pieces on the central four files on ranks 2--4. Safe
673 // squares one, two or three squares behind a friendly pawn are counted
674 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
675 // improve play on game opening.
676
677 template<Tracing T> template<Color Us>
678 Score Evaluation<T>::space() const {
679
680 if (pos.non_pawn_material() < SpaceThreshold)
681 return SCORE_ZERO;
682
683 constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
684 constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
685 constexpr Bitboard SpaceMask =
686 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
687 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
688
689 // Find the available squares for our pieces inside the area defined by SpaceMask
690 Bitboard safe = SpaceMask
691 & ~pos.pieces(Us, PAWN)
692 & ~attackedBy[Them][PAWN];
693
694 // Find all squares which are at most three squares behind some friendly pawn
695 Bitboard behind = pos.pieces(Us, PAWN);
696 behind |= shift<Down>(behind);
697 behind |= shift<Down+Down>(behind);
698
699 int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
700 int weight = pos.count<ALL_PIECES>(Us) - 1;
701 Score score = make_score(bonus * weight * weight / 16, 0);
702
703 if (T)
704 Trace::add(SPACE, Us, score);
705
706 return score;
707 }
708
709
710 // Evaluation::initiative() computes the initiative correction value
711 // for the position. It is a second order bonus/malus based on the
712 // known attacking/defending status of the players.
713
714 template<Tracing T>
715 Score Evaluation<T>::initiative(Value eg) const {
716
717 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
718 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
719
720 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
721 && (pos.pieces(PAWN) & KingSide);
722
723 // Compute the initiative bonus for the attacking side
724 int complexity = 9 * pe->passed_count()
725 + 11 * pos.count<PAWN>()
726 + 9 * outflanking
727 + 18 * pawnsOnBothFlanks
728 + 49 * !pos.non_pawn_material()
729 -103 ;
730
731 // Now apply the bonus: note that we find the attacking side by extracting
732 // the sign of the endgame value, and that we carefully cap the bonus so
733 // that the endgame score will never change sign after the bonus.
734 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
735
736 if (T)
737 Trace::add(INITIATIVE, make_score(0, v));
738
739 return make_score(0, v);
740 }
741
742
743 // Evaluation::scale_factor() computes the scale factor for the winning side
744
745 template<Tracing T>
746 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
747
748 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
749 int sf = me->scale_factor(pos, strongSide);
750
751 // If scale is not already specific, scale down the endgame via general heuristics
752 if (sf == SCALE_FACTOR_NORMAL)
753 {
754 if ( pos.opposite_bishops()
755 && pos.non_pawn_material() == 2 * BishopValueMg)
756 sf = 16 + 4 * pe->passed_count();
757 else
758 sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
759
760 }
761
762 return ScaleFactor(sf);
763 }
764
765
766 // Evaluation::value() is the main function of the class. It computes the various
767 // parts of the evaluation and returns the value of the position from the point
768 // of view of the side to move.
769
770 template<Tracing T>
771 Value Evaluation<T>::value() {
772
773 assert(!pos.checkers());
774
775 // Probe the material hash table
776 me = Material::probe(pos);
777
778 // If we have a specialized evaluation function for the current material
779 // configuration, call it and return.
780 if (me->specialized_eval_exists())
781 return me->evaluate(pos);
782
783 // Initialize score by reading the incrementally updated scores included in
784 // the position object (material + piece square tables) and the material
785 // imbalance. Score is computed internally from the white point of view.
786 Score score = pos.psq_score() + me->imbalance() + pos.this_thread()->contempt;
787
788 // Probe the pawn hash table
789 pe = Pawns::probe(pos);
790 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
791
792 // Early exit if score is high
793 Value v = (mg_value(score) + eg_value(score)) / 2;
794 if (abs(v) > LazyThreshold + pos.non_pawn_material() / 64)
795 return pos.side_to_move() == WHITE ? v : -v;
796
797 // Main evaluation begins here
798
799 initialize<WHITE>();
800 initialize<BLACK>();
801
802 // Pieces should be evaluated first (populate attack tables)
803 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
804 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
805 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
806 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
807
808 score += mobility[WHITE] - mobility[BLACK];
809
810 score += king< WHITE>() - king< BLACK>()
811 + threats<WHITE>() - threats<BLACK>()
812 + passed< WHITE>() - passed< BLACK>()
813 + space< WHITE>() - space< BLACK>();
814
815 score += initiative(eg_value(score));
816
817 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
818 ScaleFactor sf = scale_factor(eg_value(score));
819 v = mg_value(score) * int(me->game_phase())
820 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
821
822 v /= PHASE_MIDGAME;
823
824 // In case of tracing add all remaining individual evaluation terms
825 if (T)
826 {
827 Trace::add(MATERIAL, pos.psq_score());
828 Trace::add(IMBALANCE, me->imbalance());
829 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
830 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
831 Trace::add(TOTAL, score);
832 }
833
834 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
835 + Eval::Tempo;
836 }
837
838} // namespace
839
840
841/// evaluate() is the evaluator for the outer world. It returns a static
842/// evaluation of the position from the point of view of the side to move.
843
844Value Eval::evaluate(const Position& pos) {
845 return Evaluation<NO_TRACE>(pos).value();
846}
847
848
849/// trace() is like evaluate(), but instead of returning a value, it returns
850/// a string (suitable for outputting to stdout) that contains the detailed
851/// descriptions and values of each evaluation term. Useful for debugging.
852
853std::string Eval::trace(const Position& pos) {
854
855 std::memset(scores, 0, sizeof(scores));
856
857 pos.this_thread()->contempt = SCORE_ZERO; // Reset any dynamic contempt
858
859 Value v = Evaluation<TRACE>(pos).value();
860
861 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
862
863 std::stringstream ss;
864 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
865 << " Term | White | Black | Total \n"
866 << " | MG EG | MG EG | MG EG \n"
867 << " ------------+-------------+-------------+------------\n"
868 << " Material | " << Term(MATERIAL)
869 << " Imbalance | " << Term(IMBALANCE)
870 << " Pawns | " << Term(PAWN)
871 << " Knights | " << Term(KNIGHT)
872 << " Bishops | " << Term(BISHOP)
873 << " Rooks | " << Term(ROOK)
874 << " Queens | " << Term(QUEEN)
875 << " Mobility | " << Term(MOBILITY)
876 << " King safety | " << Term(KING)
877 << " Threats | " << Term(THREAT)
878 << " Passed | " << Term(PASSED)
879 << " Space | " << Term(SPACE)
880 << " Initiative | " << Term(INITIATIVE)
881 << " ------------+-------------+-------------+------------\n"
882 << " Total | " << Term(TOTAL);
883
884 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";
885
886 return ss.str();
887}
888