mirror of
https://github.com/sockspls/badfish
synced 2025-04-29 16:23:09 +00:00
281 lines
9.5 KiB
C++
281 lines
9.5 KiB
C++
/*
|
|
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
|
|
Copyright (C) 2004-2020 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
|
|
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 "bitboard.h"
|
|
#include "pawns.h"
|
|
#include "position.h"
|
|
#include "thread.h"
|
|
|
|
namespace {
|
|
|
|
#define V Value
|
|
#define S(mg, eg) make_score(mg, eg)
|
|
|
|
// Pawn penalties
|
|
constexpr Score Backward = S( 8, 27);
|
|
constexpr Score Doubled = S(11, 55);
|
|
constexpr Score Isolated = S( 5, 17);
|
|
constexpr Score WeakLever = S( 2, 54);
|
|
constexpr Score WeakUnopposed = S(15, 25);
|
|
|
|
// Bonus for blocked pawns at 5th or 6th rank
|
|
constexpr Score BlockedPawn[2] = { S(-13, -4), S(-4, 3) };
|
|
|
|
constexpr Score BlockedStorm[RANK_NB] = {
|
|
S(0, 0), S(0, 0), S(76, 78), S(-10, 15), S(-7, 10), S(-4, 6), S(-1, 2)
|
|
};
|
|
|
|
// Connected pawn bonus
|
|
constexpr int Connected[RANK_NB] = { 0, 7, 8, 11, 24, 45, 85 };
|
|
|
|
// 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( -6), V( 81), V( 93), V( 58), V( 39), V( 18), V( 25) },
|
|
{ V(-43), V( 61), V( 35), V(-49), V(-29), V(-11), V( -63) },
|
|
{ V(-10), V( 75), V( 23), V( -2), V( 32), V( 3), V( -45) },
|
|
{ V(-39), V(-13), V(-29), V(-52), V(-48), V(-67), V(-166) }
|
|
};
|
|
|
|
// 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( 85), V(-289), V(-166), V(97), V(50), V( 45), V( 50) },
|
|
{ V( 46), V( -25), V( 122), V(45), V(37), V(-10), V( 20) },
|
|
{ V( -6), V( 51), V( 168), V(34), V(-2), V(-22), V(-14) },
|
|
{ V(-15), V( -11), V( 101), V( 4), V(11), V(-15), V(-29) }
|
|
};
|
|
|
|
#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) {
|
|
|
|
constexpr Color Them = ~Us;
|
|
constexpr Direction Up = pawn_push(Us);
|
|
|
|
Bitboard neighbours, stoppers, support, phalanx, opposed;
|
|
Bitboard lever, leverPush, blocked;
|
|
Square s;
|
|
bool backward, passed, doubled;
|
|
Score score = SCORE_ZERO;
|
|
const Square* pl = pos.squares<PAWN>(Us);
|
|
|
|
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->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)
|
|
{
|
|
assert(pos.piece_on(s) == make_piece(Us, PAWN));
|
|
|
|
Rank r = relative_rank(Us, s);
|
|
|
|
// 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 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 (support | phalanx)
|
|
{
|
|
int v = Connected[r] * (2 + bool(phalanx) - bool(opposed))
|
|
+ 21 * popcount(support);
|
|
|
|
score += make_score(v, v * (r - 2) / 4);
|
|
}
|
|
|
|
else if (!neighbours)
|
|
{
|
|
if ( opposed
|
|
&& (ourPawns & forward_file_bb(Them, s))
|
|
&& !(theirPawns & adjacent_files_bb(s)))
|
|
score -= Doubled;
|
|
else
|
|
score -= Isolated
|
|
+ WeakUnopposed * !opposed;
|
|
}
|
|
|
|
else if (backward)
|
|
score -= Backward
|
|
+ WeakUnopposed * !opposed;
|
|
|
|
if (!support)
|
|
score -= Doubled * doubled
|
|
+ WeakLever * more_than_one(lever);
|
|
|
|
if (blocked && r > RANK_4)
|
|
score += BlockedPawn[r-4];
|
|
}
|
|
|
|
return score;
|
|
}
|
|
|
|
} // namespace
|
|
|
|
namespace Pawns {
|
|
|
|
|
|
/// 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 = pos.this_thread()->pawnsTable[key];
|
|
|
|
if (e->key == key)
|
|
return e;
|
|
|
|
e->key = key;
|
|
e->blockedCount = 0;
|
|
e->scores[WHITE] = evaluate<WHITE>(pos, e);
|
|
e->scores[BLACK] = evaluate<BLACK>(pos, e);
|
|
|
|
return e;
|
|
}
|
|
|
|
|
|
/// 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>
|
|
Score Entry::evaluate_shelter(const Position& pos, Square ksq) const {
|
|
|
|
constexpr Color Them = ~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);
|
|
|
|
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 & 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;
|
|
|
|
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 bonus;
|
|
}
|
|
|
|
|
|
/// 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::do_king_safety(const Position& pos) {
|
|
|
|
Square ksq = pos.square<KING>(Us);
|
|
kingSquares[Us] = ksq;
|
|
castlingRights[Us] = pos.castling_rights(Us);
|
|
auto compare = [](Score a, Score b) { return mg_value(a) < mg_value(b); };
|
|
|
|
Score shelter = evaluate_shelter<Us>(pos, ksq);
|
|
|
|
// If we can castle use the bonus after castling if it is bigger
|
|
|
|
if (pos.can_castle(Us & KING_SIDE))
|
|
shelter = std::max(shelter, evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1)), compare);
|
|
|
|
if (pos.can_castle(Us & QUEEN_SIDE))
|
|
shelter = std::max(shelter, evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1)), compare);
|
|
|
|
// In endgame we like to bring our king near our closest pawn
|
|
Bitboard pawns = pos.pieces(Us, PAWN);
|
|
int minPawnDist = 6;
|
|
|
|
if (pawns & attacks_bb<KING>(ksq))
|
|
minPawnDist = 1;
|
|
else while (pawns)
|
|
minPawnDist = std::min(minPawnDist, distance(ksq, pop_lsb(&pawns)));
|
|
|
|
return shelter - make_score(0, 16 * minPawnDist);
|
|
}
|
|
|
|
// Explicit template instantiation
|
|
template Score Entry::do_king_safety<WHITE>(const Position& pos);
|
|
template Score Entry::do_king_safety<BLACK>(const Position& pos);
|
|
|
|
} // namespace Pawns
|