/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
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"
namespace {
#define V Value
#define S(mg, eg) make_score(mg, eg)
- // Doubled pawn penalty by opposed flag and file
- const Score Doubled[2][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) },
- { 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) }};
-
- // Pawn chain membership bonus by file
- const Score ChainMember[FILE_NB] = {
- S(11,-1), S(13,-1), S(13,-1), S(14,-1),
- S(14,-1), S(13,-1), S(13,-1), S(11,-1)
+ // Pawn penalties
+ constexpr Score Backward = S( 6, 23);
+ constexpr Score Doubled = S(13, 53);
+ constexpr Score DoubledEarly = S(20, 10);
+ constexpr Score Isolated = S( 2, 15);
+ constexpr Score WeakLever = S( 5, 57);
+ constexpr Score WeakUnopposed = S(16, 22);
+
+ // Bonus for blocked pawns at 5th or 6th rank
+ constexpr Score BlockedPawn[2] = { S(-15, -3), S(-6, 3) };
+
+ constexpr Score BlockedStorm[RANK_NB] = {
+ S(0, 0), S(0, 0), S(75, 78), S(-8, 16), S(-6, 10), S(-6, 6), S(0, 2)
};
- // Candidate passed pawn bonus by rank
- const Score CandidatePassed[RANK_NB] = {
- S( 0, 0), S( 6, 13), S(6,13), S(14,29),
- S(34,68), S(83,166), S(0, 0), S( 0, 0)
+ // Connected pawn bonus
+ constexpr int Connected[RANK_NB] = { 0, 5, 7, 11, 24, 48, 86 };
+
+ // 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( -5), V( 82), V( 92), V( 54), V( 36), V( 22), V( 28) },
+ { V(-44), V( 63), V( 33), V(-50), V(-30), V(-12), V( -62) },
+ { V(-11), V( 77), V( 22), V( -6), V( 31), V( 8), V( -45) },
+ { V(-39), V(-12), V(-29), V(-50), V(-43), V(-68), V(-164) }
};
- // Weakness of our pawn shelter in front of the king indexed by [rank]
- const Value ShelterWeakness[RANK_NB] =
- { V(100), V(0), V(27), V(73), V(92), V(101), V(101) };
+ // Danger of enemy pawns moving toward our king by [distance from edge][rank].
+ // RANK_1 = 0 is used for files where the enemy has no pawn, or their pawn
+ // is behind our king. Note that UnblockedStorm[0][1-2] accommodate opponent pawn
+ // on edge, likely blocked by our king.
+ constexpr Value UnblockedStorm[int(FILE_NB) / 2][RANK_NB] = {
+ { V( 87), V(-288), V(-168), V( 96), V( 47), V( 44), V( 46) },
+ { V( 42), V( -25), V( 120), V( 45), V( 34), V( -9), V( 24) },
+ { V( -8), V( 51), V( 167), V( 35), V( -4), V(-16), V(-12) },
+ { V(-17), V( -13), V( 100), V( 4), V( 9), V(-16), V(-31) }
+ };
- // Danger of enemy pawns moving toward our king indexed by
- // [no friendly pawn | pawn unblocked | pawn blocked][rank of enemy pawn]
- const Value StormDanger[3][RANK_NB] = {
- { V( 0), V(64), V(128), V(51), V(26) },
- { V(26), V(32), V( 96), V(38), V(20) },
- { V( 0), V( 0), V( 64), V(25), V(13) }};
- // Max bonus for king safety. Corresponds to start position with all the pawns
- // in front of the king and no enemy pawn on the horizont.
- const Value MaxSafetyBonus = V(263);
+ // KingOnFile[semi-open Us][semi-open Them] contains bonuses/penalties
+ // for king when the king is on a semi-open or open file.
+ constexpr Score KingOnFile[2][2] = {{ S(-21,10), S(-7, 1) },
+ { S( 0,-3), S( 9,-4) }};
#undef S
#undef V
+
+ /// evaluate() calculates a score for the static pawn structure of the given position.
+ /// We cannot use the location of pieces or king in this function, as the evaluation
+ /// of the pawn structure will be stored in a small cache for speed reasons, and will
+ /// be re-used even when the pieces have moved.
+
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;
+ constexpr Direction Up = pawn_push(Us);
+ constexpr Direction Down = -Up;
- Bitboard b;
+ Bitboard neighbours, stoppers, support, phalanx, opposed;
+ Bitboard lever, leverPush, blocked;
Square s;
- File f;
- bool passed, isolated, doubled, opposed, chain, backward, candidate;
- Score value = SCORE_ZERO;
- const Square* pl = pos.list<PAWN>(Us);
+ bool backward, passed, doubled;
+ Score score = SCORE_ZERO;
+ Bitboard b = pos.pieces(Us, PAWN);
- Bitboard ourPawns = pos.pieces(Us, PAWN);
+ Bitboard ourPawns = pos.pieces( Us, PAWN);
Bitboard theirPawns = pos.pieces(Them, PAWN);
+ Bitboard doubleAttackThem = pawn_double_attacks_bb<Them>(theirPawns);
+
e->passedPawns[Us] = 0;
e->kingSquares[Us] = SQ_NONE;
- e->semiopenFiles[Us] = 0xFF;
- e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
- e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
- e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
+ e->pawnAttacks[Us] = e->pawnAttacksSpan[Us] = pawn_attacks_bb<Us>(ourPawns);
+ e->blockedCount += popcount(shift<Up>(ourPawns) & (theirPawns | doubleAttackThem));
// Loop through all pawns of the current color and score each pawn
- while ((s = *pl++) != SQ_NONE)
- {
+ while (b) {
+ s = pop_lsb(&b);
+
assert(pos.piece_on(s) == make_piece(Us, PAWN));
- f = file_of(s);
-
- // This file cannot be semi-open
- e->semiopenFiles[Us] &= ~(1 << f);
-
- // Our rank plus previous one. Used for chain detection
- b = rank_bb(s) | rank_bb(s - pawn_push(Us));
-
- // Flag the pawn as passed, isolated, doubled or member of a pawn
- // chain (but not the backward one).
- chain = ourPawns & adjacent_files_bb(f) & b;
- 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));
-
- // Test for backward pawn.
- // If the pawn is passed, isolated, or member of a pawn chain it cannot
- // be backward. If there are friendly pawns behind on adjacent files
- // or if can capture an enemy pawn it cannot be backward either.
- if ( (passed | isolated | chain)
- || (ourPawns & pawn_attack_span(Them, s))
- || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
- 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 seeing whether we meet a friendly or an enemy pawn first.
- b = pos.attacks_from<PAWN>(s, Us);
-
- // Note that we are sure to find something because pawn is not passed
- // nor isolated, so loop is potentially infinite, but it isn't.
- while (!(b & (ourPawns | theirPawns)))
- b = shift_bb<Up>(b);
-
- // The friendly pawn needs to be at least two ranks closer than the
- // enemy pawn in order to help the potentially backward pawn advance.
- backward = (b | shift_bb<Up>(b)) & theirPawns;
- }
+ Rank r = relative_rank(Us, s);
- assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
+ // Flag the pawn
+ opposed = theirPawns & forward_file_bb(Us, s);
+ blocked = theirPawns & (s + Up);
+ stoppers = theirPawns & passed_pawn_span(Us, s);
+ lever = theirPawns & pawn_attacks_bb(Us, s);
+ leverPush = theirPawns & pawn_attacks_bb(Us, s + Up);
+ doubled = ourPawns & (s - Up);
+ neighbours = ourPawns & adjacent_files_bb(s);
+ phalanx = neighbours & rank_bb(s);
+ support = neighbours & rank_bb(s - Up);
- // A not passed pawn is a candidate to become passed if it is free to
- // advance and if the number of friendly pawns beside or behind this
- // pawn on adjacent files is higher or equal than the number of
- // enemy pawns in the forward direction on the adjacent files.
- candidate = !(opposed | passed | backward | isolated)
- && (b = pawn_attack_span(Them, s + pawn_push(Us)) & ourPawns) != 0
- && popcount<Max15>(b) >= popcount<Max15>(pawn_attack_span(Us, s) & theirPawns);
+ if (doubled)
+ {
+ // Additional doubled penalty if none of their pawns is fixed
+ if (!(ourPawns & shift<Down>(theirPawns | pawn_attacks_bb<Them>(theirPawns))))
+ score -= DoubledEarly;
+ }
- // 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)
+ // A pawn is backward when it is behind all pawns of the same color on
+ // the adjacent files and cannot safely advance.
+ backward = !(neighbours & forward_ranks_bb(Them, s + Up))
+ && (leverPush | blocked);
+
+ // Compute additional span if pawn is not backward nor blocked
+ if (!backward && !blocked)
+ e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
+
+ // A pawn is passed if one of the three following conditions is true:
+ // (a) there is no stoppers except some levers
+ // (b) the only stoppers are the leverPush, but we outnumber them
+ // (c) there is only one front stopper which can be levered.
+ // (Refined in Evaluation::passed)
+ passed = !(stoppers ^ lever)
+ || ( !(stoppers ^ leverPush)
+ && popcount(phalanx) >= popcount(leverPush))
+ || ( stoppers == blocked && r >= RANK_5
+ && (shift<Up>(support) & ~(theirPawns | doubleAttackThem)));
+
+ passed &= !(forward_file_bb(Us, s) & ourPawns);
+
+ // Passed pawns will be properly scored later in evaluation when we have
+ // full attack info.
+ if (passed)
e->passedPawns[Us] |= s;
// Score this pawn
- if (isolated)
- value -= Isolated[opposed][f];
+ if (support | phalanx)
+ {
+ int v = Connected[r] * (2 + bool(phalanx) - bool(opposed))
+ + 22 * popcount(support);
- if (doubled)
- value -= Doubled[opposed][f];
+ score += make_score(v, v * (r - 2) / 4);
+ }
- if (backward)
- value -= Backward[opposed][f];
+ else if (!neighbours)
+ {
+ if ( opposed
+ && (ourPawns & forward_file_bb(Them, s))
+ && !(theirPawns & adjacent_files_bb(s)))
+ score -= Doubled;
+ else
+ score -= Isolated
+ + WeakUnopposed * !opposed;
+ }
- if (chain)
- value += ChainMember[f];
+ else if (backward)
+ score -= Backward
+ + WeakUnopposed * !opposed * bool(~(FileABB | FileHBB) & s);
- if (candidate)
- value += CandidatePassed[relative_rank(Us, s)];
+ if (!support)
+ score -= Doubled * doubled
+ + WeakLever * more_than_one(lever);
+
+ if (blocked && r >= RANK_5)
+ score += BlockedPawn[r - RANK_5];
}
- return value;
+ return score;
}
} // namespace
namespace Pawns {
-/// probe() takes a position object as input, computes a Entry object, and returns
-/// a pointer to it. The result is also stored in a hash table, so we don't have
-/// to recompute everything when the same pawn structure occurs again.
-Entry* probe(const Position& pos, Table& entries) {
+/// Pawns::probe() looks up the current position's pawns configuration in
+/// the pawns hash table. It returns a pointer to the Entry if the position
+/// is found. Otherwise a new Entry is computed and stored there, so we don't
+/// have to recompute all when the same pawns configuration occurs again.
+
+Entry* probe(const Position& pos) {
Key key = pos.pawn_key();
- Entry* e = entries[key];
+ Entry* e = pos.this_thread()->pawnsTable[key];
if (e->key == key)
return e;
e->key = key;
- e->value = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
+ e->blockedCount = 0;
+ e->scores[WHITE] = evaluate<WHITE>(pos, e);
+ e->scores[BLACK] = evaluate<BLACK>(pos, e);
+
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) {
+Score Entry::evaluate_shelter(const Position& pos, Square ksq) const {
- const Color Them = (Us == WHITE ? BLACK : WHITE);
+ constexpr Color Them = ~Us;
- Value safety = MaxSafetyBonus;
- Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
- Bitboard ourPawns = b & pos.pieces(Us);
+ Bitboard b = pos.pieces(PAWN) & ~forward_ranks_bb(Them, ksq);
+ Bitboard ourPawns = b & pos.pieces(Us) & ~pawnAttacks[Them];
Bitboard theirPawns = b & pos.pieces(Them);
- Rank rkUs, rkThem;
- File kf = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
- for (int f = kf - 1; f <= kf + 1; f++)
+ Score bonus = make_score(5, 5);
+
+ File center = std::clamp(file_of(ksq), FILE_B, FILE_G);
+ for (File f = File(center - 1); f <= File(center + 1); ++f)
{
- b = ourPawns & FileBB[f];
- rkUs = b ? relative_rank(Us, lsb(Us, b)) : RANK_1;
- safety -= ShelterWeakness[rkUs];
+ b = ourPawns & file_bb(f);
+ int ourRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : 0;
+
+ b = theirPawns & file_bb(f);
+ int theirRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : 0;
- b = theirPawns & FileBB[f];
- rkThem = b ? relative_rank(Us, lsb(Us, b)) : RANK_1;
- safety -= StormDanger[rkUs == RANK_1 ? 0 : rkThem == rkUs + 1 ? 2 : 1][rkThem];
+ int d = edge_distance(f);
+ bonus += make_score(ShelterStrength[d][ourRank], 0);
+
+ if (ourRank && (ourRank == theirRank - 1))
+ bonus -= BlockedStorm[theirRank];
+ else
+ bonus -= make_score(UnblockedStorm[d][theirRank], 0);
}
- return safety;
+ // King On File
+ bonus -= KingOnFile[pos.is_on_semiopen_file(Us, ksq)][pos.is_on_semiopen_file(Them, ksq)];
+
+ return bonus;
}
-/// Entry::update_safety() calculates and caches a bonus for king safety. It is
-/// called only when king square changes, about 20% of total king_safety() calls.
+/// Entry::do_king_safety() calculates a bonus for king safety. It is called only
+/// when king square changes, which is about 20% of total king_safety() calls.
template<Color Us>
-Score Entry::update_safety(const Position& pos, Square ksq) {
+Score Entry::do_king_safety(const Position& pos) {
+ Square ksq = pos.square<KING>(Us);
kingSquares[Us] = ksq;
- castleRights[Us] = pos.can_castle(Us);
- minKPdistance[Us] = 0;
+ castlingRights[Us] = pos.castling_rights(Us);
+ auto compare = [](Score a, Score b) { return mg_value(a) < mg_value(b); };
- Bitboard pawns = pos.pieces(Us, PAWN);
- if (pawns)
- while (!(DistanceRingsBB[ksq][minKPdistance[Us]++] & pawns)) {}
+ Score shelter = evaluate_shelter<Us>(pos, ksq);
+
+ // If we can castle use the bonus after castling if it is bigger
- if (relative_rank(Us, ksq) > RANK_4)
- return kingSafety[Us] = make_score(0, -16 * minKPdistance[Us]);
+ if (pos.can_castle(Us & KING_SIDE))
+ shelter = std::max(shelter, evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1)), compare);
- Value bonus = shelter_storm<Us>(pos, ksq);
+ if (pos.can_castle(Us & QUEEN_SIDE))
+ shelter = std::max(shelter, evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1)), compare);
- // If we can castle use the bonus after the castle if is bigger
- if (pos.can_castle(make_castle_right(Us, KING_SIDE)))
- bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
+ // In endgame we like to bring our king near our closest pawn
+ Bitboard pawns = pos.pieces(Us, PAWN);
+ int minPawnDist = 6;
- if (pos.can_castle(make_castle_right(Us, QUEEN_SIDE)))
- bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
+ if (pawns & attacks_bb<KING>(ksq))
+ minPawnDist = 1;
+ else while (pawns)
+ minPawnDist = std::min(minPawnDist, distance(ksq, pop_lsb(&pawns)));
- return kingSafety[Us] = make_score(bonus, -16 * minKPdistance[Us]);
+ return shelter - make_score(0, 16 * minPawnDist);
}
// Explicit template instantiation
-template Score Entry::update_safety<WHITE>(const Position& pos, Square ksq);
-template Score Entry::update_safety<BLACK>(const Position& pos, Square ksq);
+template Score Entry::do_king_safety<WHITE>(const Position& pos);
+template Score Entry::do_king_safety<BLACK>(const Position& pos);
} // namespace Pawns
projects / stockfish / blobdiff