Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, 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
#include <cassert>
#include "bitboard.h"
-#include "bitcount.h"
#include "pawns.h"
#include "position.h"
#include "thread.h"
#define V Value
#define S(mg, eg) make_score(mg, eg)
- // Doubled pawn penalty by file
- const Score Doubled[FILE_NB] = {
- S(13, 43), S(20, 48), S(23, 48), S(23, 48),
- S(23, 48), S(23, 48), S(20, 48), S(13, 43) };
-
- // Isolated pawn penalty by opposed flag and file
- const Score Isolated[2][FILE_NB] = {
- { S(37, 45), S(54, 52), S(60, 52), S(60, 52),
- S(60, 52), S(60, 52), S(54, 52), S(37, 45) },
- { S(25, 30), S(36, 35), S(40, 35), S(40, 35),
- S(40, 35), S(40, 35), S(36, 35), S(25, 30) } };
-
- // Backward pawn penalty by opposed flag and file
- const Score Backward[2][FILE_NB] = {
- { S(30, 42), S(43, 46), S(49, 46), S(49, 46),
- S(49, 46), S(49, 46), S(43, 46), S(30, 42) },
- { S(20, 28), S(29, 31), S(33, 31), S(33, 31),
- S(33, 31), S(33, 31), S(29, 31), S(20, 28) } };
-
- // Connected pawn bonus by opposed, phalanx flags and rank
- Score Connected[2][2][RANK_NB];
-
- // Levers bonus by rank
- const Score Lever[RANK_NB] = {
- S( 0, 0), S( 0, 0), S(0, 0), S(0, 0),
- S(20,20), S(40,40), S(0, 0), S(0, 0) };
-
- // Unsupported pawn penalty
- const Score UnsupportedPawnPenalty = S(20, 10);
-
- // Weakness of our pawn shelter in front of the king by [distance from edge][rank]
- const Value ShelterWeakness[][RANK_NB] = {
- { V( 99), V(23), V(24), V(54), V(85), V( 93), V(107) },
- { V(119), V( 2), V(28), V(72), V(96), V(104), V(114) },
- { V(103), V( 6), V(47), V(74), V(84), V(103), V( 94) },
- { V( 78), V(10), V(41), V(64), V(88), V( 92), V(115) } };
-
- // Danger of enemy pawns moving toward our king by [type][distance from edge][rank]
- const Value StormDanger[][4][RANK_NB] = {
- { { V( 0), V( 65), V( 125), V(37), V(30) },
- { V( 0), V( 57), V( 136), V(39), V(24) },
- { V( 0), V( 50), V( 114), V(45), V(29) },
- { V( 0), V( 58), V( 129), V(56), V(34) } },
- { { V(20), V( 45), V( 91), V(47), V(20) },
- { V(25), V( 23), V( 105), V(38), V(14) },
- { V(21), V( 37), V( 99), V(35), V(21) },
- { V(30), V( 18), V( 105), V(38), V(28) } },
- { { V( 0), V( 0), V( 81), V(13), V( 4) },
- { V( 0), V( 0), V( 169), V(30), V( 4) },
- { V( 0), V( 0), V( 166), V(24), V( 6) },
- { V( 0), V( 0), V( 164), V(24), V(11) } },
- { { V( 0), V(-289), V(-297), V(57), V(29) },
- { V( 0), V( 66), V( 136), V(43), V(16) },
- { V( 0), V( 66), V( 141), V(50), V(31) },
- { V( 0), V( 63), V( 126), V(52), V(23) } } };
-
- // Max bonus for king safety. Corresponds to start position with all the pawns
- // in front of the king and no enemy pawn on the horizon.
- const Value MaxSafetyBonus = V(252);
+ // Isolated pawn penalty
+ constexpr Score Isolated = S(13, 18);
+
+ // Backward pawn penalty
+ constexpr Score Backward = S(24, 12);
+
+ // Connected pawn bonus by opposed, phalanx, #support and rank
+ Score Connected[2][2][3][RANK_NB];
+
+ // Doubled pawn penalty
+ constexpr Score Doubled = S(18, 38);
+
+ // Strength of pawn shelter for our king by [distance from edge][rank].
+ // RANK_1 = 0 is used for files where we have no pawn, or pawn is behind our king.
+ constexpr Value ShelterStrength[int(FILE_NB) / 2][RANK_NB] = {
+ { V( -9), V(64), V(77), V( 44), V( 4), V( -1), V(-11) },
+ { V(-15), V(83), V(51), V(-10), V( 1), V(-10), V(-28) },
+ { V(-18), V(84), V(27), V(-12), V(21), V( -7), V(-36) },
+ { V( 12), V(79), V(25), V( 19), V( 9), V( -6), V(-33) }
+ };
+
+ // Danger of enemy pawns moving toward our king by [type][distance from edge][rank].
+ // For the unopposed and unblocked cases, RANK_1 = 0 is used when opponent has
+ // no pawn on the given file, or their pawn is behind our king.
+ constexpr Value StormDanger[][4][RANK_NB] = {
+ { { V( 4), V( 73), V( 132), V(46), V(31) }, // Unopposed
+ { V( 1), V( 64), V( 143), V(26), V(13) },
+ { V( 1), V( 47), V( 110), V(44), V(24) },
+ { V( 0), V( 72), V( 127), V(50), V(31) } },
+ { { V( 0), V( 0), V( 19), V(23), V( 1) }, // BlockedByPawn
+ { V( 0), V( 0), V( 88), V(27), V( 2) },
+ { V( 0), V( 0), V( 101), V(16), V( 1) },
+ { V( 0), V( 0), V( 111), V(22), V(15) } },
+ { { V(22), V( 45), V( 104), V(62), V( 6) }, // Unblocked
+ { V(31), V( 30), V( 99), V(39), V(19) },
+ { V(23), V( 29), V( 96), V(41), V(15) },
+ { V(21), V( 23), V( 116), V(41), V(15) } }
+ };
#undef S
#undef V
template<Color Us>
Score evaluate(const Position& pos, Pawns::Entry* e) {
- const Color Them = (Us == WHITE ? BLACK : WHITE);
- const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
- const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
- const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
+ constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
+ constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
- Bitboard b, p, doubled, connected;
+ Bitboard b, neighbours, stoppers, doubled, supported, phalanx;
+ Bitboard lever, leverPush;
Square s;
- bool passed, isolated, opposed, phalanx, backward, unsupported, lever;
+ bool opposed, backward;
Score score = SCORE_ZERO;
- const Square* pl = pos.list<PAWN>(Us);
- const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
+ const Square* pl = pos.squares<PAWN>(Us);
- Bitboard ourPawns = pos.pieces(Us , PAWN);
+ Bitboard ourPawns = pos.pieces( Us, PAWN);
Bitboard theirPawns = pos.pieces(Them, PAWN);
- e->passedPawns[Us] = 0;
- e->kingSquares[Us] = SQ_NONE;
+ e->passedPawns[Us] = e->pawnAttacksSpan[Us] = e->weakUnopposed[Us] = 0;
e->semiopenFiles[Us] = 0xFF;
- e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
- e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
+ e->kingSquares[Us] = SQ_NONE;
+ e->pawnAttacks[Us] = pawn_attacks_bb<Us>(ourPawns);
+ e->pawnsOnSquares[Us][BLACK] = popcount(ourPawns & DarkSquares);
e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
// Loop through all pawns of the current color and score each pawn
File f = file_of(s);
- // This file cannot be semi-open
- e->semiopenFiles[Us] &= ~(1 << f);
-
- // Previous rank
- p = rank_bb(s - pawn_push(Us));
-
- // Flag the pawn as passed, isolated, doubled,
- // unsupported or connected (but not the backward one).
- connected = ourPawns & adjacent_files_bb(f) & (rank_bb(s) | p);
- phalanx = connected & rank_bb(s);
- unsupported = !(ourPawns & adjacent_files_bb(f) & p);
- isolated = !(ourPawns & adjacent_files_bb(f));
- doubled = ourPawns & forward_bb(Us, s);
- opposed = theirPawns & forward_bb(Us, s);
- passed = !(theirPawns & passed_pawn_mask(Us, s));
- lever = theirPawns & pawnAttacksBB[s];
-
- // Test for backward pawn.
- // If the pawn is passed, isolated, or connected it cannot be
- // backward. If there are friendly pawns behind on adjacent files
- // or if it can capture an enemy pawn it cannot be backward either.
- if ( (passed | isolated | connected)
- || (ourPawns & pawn_attack_span(Them, s))
- || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
+ e->semiopenFiles[Us] &= ~(1 << f);
+ e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
+
+ // Flag the pawn
+ opposed = theirPawns & forward_file_bb(Us, s);
+ stoppers = theirPawns & passed_pawn_mask(Us, s);
+ lever = theirPawns & PawnAttacks[Us][s];
+ leverPush = theirPawns & PawnAttacks[Us][s + Up];
+ doubled = ourPawns & (s - Up);
+ neighbours = ourPawns & adjacent_files_bb(f);
+ phalanx = neighbours & rank_bb(s);
+ supported = neighbours & rank_bb(s - Up);
+
+ // A pawn is backward when it is behind all pawns of the same color on the
+ // adjacent files and cannot be safely advanced.
+ if (!neighbours || lever || relative_rank(Us, s) >= RANK_5)
backward = false;
else
{
- // We now know that there are no friendly pawns beside or behind this
- // pawn on adjacent files. We now check whether the pawn is
- // backward by looking in the forward direction on the adjacent
- // files, and picking the closest pawn there.
- b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
- b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
-
- // If we have an enemy pawn in the same or next rank, the pawn is
- // backward because it cannot advance without being captured.
- backward = (b | shift_bb<Up>(b)) & theirPawns;
- }
+ // Find the backmost rank with neighbours or stoppers
+ b = rank_bb(backmost_sq(Us, neighbours | stoppers));
+
+ // The pawn is backward when it cannot safely progress to that rank:
+ // either there is a stopper in the way on this rank, or there is a
+ // stopper on adjacent file which controls the way to that rank.
+ backward = (b | shift<Up>(b & adjacent_files_bb(f))) & stoppers;
- assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
+ assert(!(backward && (forward_ranks_bb(Them, s + Up) & neighbours)));
+ }
// Passed pawns will be properly scored in evaluation because we need
- // full attack info to evaluate passed pawns. Only the frontmost passed
- // pawn on each file is considered a true passed pawn.
- if (passed && !doubled)
+ // full attack info to evaluate them. Include also not passed pawns
+ // which could become passed after one or two pawn pushes when are
+ // not attacked more times than defended.
+ if ( !(stoppers ^ lever ^ leverPush)
+ && !(ourPawns & forward_file_bb(Us, s))
+ && popcount(supported) >= popcount(lever) - 1
+ && popcount(phalanx) >= popcount(leverPush))
e->passedPawns[Us] |= s;
- // Score this pawn
- if (isolated)
- score -= Isolated[opposed][f];
-
- if (unsupported && !isolated)
- score -= UnsupportedPawnPenalty;
+ else if ( stoppers == SquareBB[s + Up]
+ && relative_rank(Us, s) >= RANK_5)
+ {
+ b = shift<Up>(supported) & ~theirPawns;
+ while (b)
+ if (!more_than_one(theirPawns & PawnAttacks[Us][pop_lsb(&b)]))
+ e->passedPawns[Us] |= s;
+ }
- if (doubled)
- score -= Doubled[f] / distance<Rank>(s, frontmost_sq(Us, doubled));
+ // Score this pawn
+ if (supported | phalanx)
+ score += Connected[opposed][bool(phalanx)][popcount(supported)][relative_rank(Us, s)];
- if (backward)
- score -= Backward[opposed][f];
+ else if (!neighbours)
+ score -= Isolated, e->weakUnopposed[Us] += !opposed;
- if (connected)
- score += Connected[opposed][phalanx][relative_rank(Us, s)];
+ else if (backward)
+ score -= Backward, e->weakUnopposed[Us] += !opposed;
- if (lever)
- score += Lever[relative_rank(Us, s)];
+ if (doubled && !supported)
+ score -= Doubled;
}
- b = e->semiopenFiles[Us] ^ 0xFF;
- e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
-
return score;
}
/// hard-coded tables, when makes sense, we prefer to calculate them with a formula
/// to reduce independent parameters and to allow easier tuning and better insight.
-void init()
-{
- static const int Seed[RANK_NB] = { 0, 6, 15, 10, 57, 75, 135, 258 };
+void init() {
+
+ static constexpr int Seed[RANK_NB] = { 0, 13, 24, 18, 76, 100, 175, 330 };
for (int opposed = 0; opposed <= 1; ++opposed)
for (int phalanx = 0; phalanx <= 1; ++phalanx)
- for (Rank r = RANK_2; r < RANK_8; ++r)
- {
- int bonus = Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0);
- Connected[opposed][phalanx][r] = make_score(bonus / 2, bonus >> opposed);
- }
+ for (int support = 0; support <= 2; ++support)
+ for (Rank r = RANK_2; r < RANK_8; ++r)
+ {
+ int v = 17 * support;
+ v += (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
+
+ Connected[opposed][phalanx][support][r] = make_score(v, v * (r - 2) / 4);
+ }
}
return e;
e->key = key;
- e->score = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
+ e->scores[WHITE] = evaluate<WHITE>(pos, e);
+ e->scores[BLACK] = evaluate<BLACK>(pos, e);
+ e->openFiles = popcount(e->semiopenFiles[WHITE] & e->semiopenFiles[BLACK]);
+ e->asymmetry = popcount( (e->passedPawns[WHITE] | e->passedPawns[BLACK])
+ | (e->semiopenFiles[WHITE] ^ e->semiopenFiles[BLACK]));
+
return e;
}
-/// Entry::shelter_storm() calculates shelter and storm penalties for the file
-/// the king is on, as well as the two adjacent files.
+/// Entry::evaluate_shelter() calculates the shelter bonus and the storm
+/// penalty for a king, looking at the king file and the two closest files.
template<Color Us>
-Value Entry::shelter_storm(const Position& pos, Square ksq) {
-
- const Color Them = (Us == WHITE ? BLACK : WHITE);
+Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
- enum { NoFriendlyPawn, Unblocked, BlockedByPawn, BlockedByKing };
+ enum { Unopposed, BlockedByPawn, Unblocked };
+ constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
+ constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
+ constexpr Bitboard BlockRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
- Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
+ Bitboard b = pos.pieces(PAWN) & (forward_ranks_bb(Us, ksq) | rank_bb(ksq));
Bitboard ourPawns = b & pos.pieces(Us);
Bitboard theirPawns = b & pos.pieces(Them);
- Value safety = MaxSafetyBonus;
- File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
- for (File f = center - File(1); f <= center + File(1); ++f)
+ Value safety = (ourPawns & file_bb(ksq)) ? Value(5) : Value(-5);
+
+ if ((theirPawns & (FileABB | FileHBB) & BlockRanks) & (ksq + Up))
+ safety += 374;
+
+ File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
+ for (File f = File(center - 1); f <= File(center + 1); ++f)
{
b = ourPawns & file_bb(f);
Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
- b = theirPawns & file_bb(f);
+ b = theirPawns & file_bb(f);
Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
- safety -= ShelterWeakness[std::min(f, FILE_H - f)][rkUs]
- + StormDanger
- [f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing :
- rkUs == RANK_1 ? NoFriendlyPawn :
- rkThem == rkUs + 1 ? BlockedByPawn : Unblocked]
- [std::min(f, FILE_H - f)][rkThem];
+ int d = std::min(f, ~f);
+ safety += ShelterStrength[d][rkUs]
+ - StormDanger[rkUs == RANK_1 ? Unopposed :
+ rkUs == rkThem - 1 ? BlockedByPawn : Unblocked]
+ [d][rkThem];
}
return safety;
kingSquares[Us] = ksq;
castlingRights[Us] = pos.can_castle(Us);
- minKingPawnDistance[Us] = 0;
+ int minKingPawnDistance = 0;
Bitboard pawns = pos.pieces(Us, PAWN);
if (pawns)
- while (!(DistanceRingBB[ksq][minKingPawnDistance[Us]++] & pawns)) {}
-
- if (relative_rank(Us, ksq) > RANK_4)
- return make_score(0, -16 * minKingPawnDistance[Us]);
+ while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {}
- Value bonus = shelter_storm<Us>(pos, ksq);
+ Value bonus = evaluate_shelter<Us>(pos, ksq);
// If we can castle use the bonus after the castling if it is bigger
if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
- bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
+ bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1)));
if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
- bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
+ bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1)));
- return make_score(bonus, -16 * minKingPawnDistance[Us]);
+ return make_score(bonus, -16 * minKingPawnDistance);
}
// Explicit template instantiation