868 lines
31 KiB
C++
868 lines
31 KiB
C++
/*
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Glaurung, a UCI chess playing engine.
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Copyright (C) 2004-2008 Tord Romstad
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Glaurung is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Glaurung is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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////
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//// Includes
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////
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#include <cassert>
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#include "bitbase.h"
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#include "endgame.h"
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////
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//// Constants and variables
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////
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/// Evaluation functions
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// Generic "mate lone king" eval:
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KXKEvaluationFunction EvaluateKXK = KXKEvaluationFunction(WHITE);
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KXKEvaluationFunction EvaluateKKX = KXKEvaluationFunction(BLACK);
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// KBN vs K:
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KBNKEvaluationFunction EvaluateKBNK = KBNKEvaluationFunction(WHITE);
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KBNKEvaluationFunction EvaluateKKBN = KBNKEvaluationFunction(BLACK);
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// KP vs K:
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KPKEvaluationFunction EvaluateKPK = KPKEvaluationFunction(WHITE);
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KPKEvaluationFunction EvaluateKKP = KPKEvaluationFunction(BLACK);
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// KR vs KP:
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KRKPEvaluationFunction EvaluateKRKP = KRKPEvaluationFunction(WHITE);
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KRKPEvaluationFunction EvaluateKPKR = KRKPEvaluationFunction(BLACK);
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// KR vs KB:
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KRKBEvaluationFunction EvaluateKRKB = KRKBEvaluationFunction(WHITE);
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KRKBEvaluationFunction EvaluateKBKR = KRKBEvaluationFunction(BLACK);
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// KR vs KN:
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KRKNEvaluationFunction EvaluateKRKN = KRKNEvaluationFunction(WHITE);
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KRKNEvaluationFunction EvaluateKNKR = KRKNEvaluationFunction(BLACK);
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// KQ vs KR:
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KQKREvaluationFunction EvaluateKQKR = KQKREvaluationFunction(WHITE);
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KQKREvaluationFunction EvaluateKRKQ = KQKREvaluationFunction(BLACK);
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/// Scaling functions
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// KBP vs K:
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KBPKScalingFunction ScaleKBPK = KBPKScalingFunction(WHITE);
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KBPKScalingFunction ScaleKKBP = KBPKScalingFunction(BLACK);
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// KQ vs KRP:
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KQKRPScalingFunction ScaleKQKRP = KQKRPScalingFunction(WHITE);
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KQKRPScalingFunction ScaleKRPKQ = KQKRPScalingFunction(BLACK);
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// KRP vs KR:
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KRPKRScalingFunction ScaleKRPKR = KRPKRScalingFunction(WHITE);
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KRPKRScalingFunction ScaleKRKRP = KRPKRScalingFunction(BLACK);
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// KRPP vs KRP:
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KRPPKRPScalingFunction ScaleKRPPKRP = KRPPKRPScalingFunction(WHITE);
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KRPPKRPScalingFunction ScaleKRPKRPP = KRPPKRPScalingFunction(BLACK);
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// King and pawns vs king:
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KPsKScalingFunction ScaleKPsK = KPsKScalingFunction(WHITE);
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KPsKScalingFunction ScaleKKPs = KPsKScalingFunction(BLACK);
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// KBP vs KB:
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KBPKBScalingFunction ScaleKBPKB = KBPKBScalingFunction(WHITE);
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KBPKBScalingFunction ScaleKBKBP = KBPKBScalingFunction(BLACK);
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// KBP vs KN:
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KBPKNScalingFunction ScaleKBPKN = KBPKNScalingFunction(WHITE);
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KBPKNScalingFunction ScaleKNKBP = KBPKNScalingFunction(BLACK);
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// KNP vs K:
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KNPKScalingFunction ScaleKNPK = KNPKScalingFunction(WHITE);
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KNPKScalingFunction ScaleKKNP = KNPKScalingFunction(BLACK);
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// KPKP
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KPKPScalingFunction ScaleKPKPw = KPKPScalingFunction(WHITE);
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KPKPScalingFunction ScaleKPKPb = KPKPScalingFunction(BLACK);
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////
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//// Local definitions
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////
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namespace {
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// Table used to drive the defending king towards the edge of the board
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// in KX vs K and KQ vs KR endgames:
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const uint8_t MateTable[64] = {
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100, 90, 80, 70, 70, 80, 90, 100,
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90, 70, 60, 50, 50, 60, 70, 90,
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80, 60, 40, 30, 30, 40, 60, 80,
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70, 50, 30, 20, 20, 30, 50, 70,
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70, 50, 30, 20, 20, 30, 50, 70,
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80, 60, 40, 30, 30, 40, 60, 80,
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90, 70, 60, 50, 50, 60, 70, 90,
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100, 90, 80, 70, 70, 80, 90, 100,
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};
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// Table used to drive the defending king towards a corner square of the
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// right color in KBN vs K endgames:
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const uint8_t KBNKMateTable[64] = {
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200, 190, 180, 170, 160, 150, 140, 130,
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190, 180, 170, 160, 150, 140, 130, 140,
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180, 170, 155, 140, 140, 125, 140, 150,
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170, 160, 140, 120, 110, 140, 150, 160,
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160, 150, 140, 110, 120, 140, 160, 170,
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150, 140, 125, 140, 140, 155, 170, 180,
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140, 130, 140, 150, 160, 170, 180, 190,
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130, 140, 150, 160, 170, 180, 190, 200
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};
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// The attacking side is given a descending bonus based on distance between
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// the two kings in basic endgames:
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const int DistanceBonus[8] = {0, 0, 100, 80, 60, 40, 20, 10};
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// Bitbase for KP vs K:
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uint8_t KPKBitbase[24576];
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// Penalty for big distance between king and knight for the defending king
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// and knight in KR vs KN endgames:
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const int KRKNKingKnightDistancePenalty[8] = { 0, 0, 4, 10, 20, 32, 48, 70 };
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// Various inline functions for accessing the above arrays:
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inline Value mate_table(Square s) {
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return Value(MateTable[s]);
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}
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inline Value kbnk_mate_table(Square s) {
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return Value(KBNKMateTable[s]);
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}
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inline Value distance_bonus(int d) {
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return Value(DistanceBonus[d]);
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}
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inline Value krkn_king_knight_distance_penalty(int d) {
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return Value(KRKNKingKnightDistancePenalty[d]);
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}
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// Function for probing the KP vs K bitbase:
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int probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm);
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}
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////
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//// Functions
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////
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/// Constructors
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EndgameEvaluationFunction::EndgameEvaluationFunction(Color c) {
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strongerSide = c;
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weakerSide = opposite_color(strongerSide);
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}
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KXKEvaluationFunction::KXKEvaluationFunction(Color c) : EndgameEvaluationFunction(c) { }
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KBNKEvaluationFunction::KBNKEvaluationFunction(Color c) : EndgameEvaluationFunction(c) { }
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KPKEvaluationFunction::KPKEvaluationFunction(Color c) : EndgameEvaluationFunction(c) { }
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KRKPEvaluationFunction::KRKPEvaluationFunction(Color c) : EndgameEvaluationFunction(c) { }
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KRKBEvaluationFunction::KRKBEvaluationFunction(Color c) : EndgameEvaluationFunction(c) { }
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KRKNEvaluationFunction::KRKNEvaluationFunction(Color c) : EndgameEvaluationFunction(c) { }
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KQKREvaluationFunction::KQKREvaluationFunction(Color c) : EndgameEvaluationFunction(c) { }
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ScalingFunction::ScalingFunction(Color c) {
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strongerSide = c;
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weakerSide = opposite_color(c);
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}
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KBPKScalingFunction::KBPKScalingFunction(Color c) : ScalingFunction(c) { }
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KQKRPScalingFunction::KQKRPScalingFunction(Color c) : ScalingFunction(c) { }
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KRPKRScalingFunction::KRPKRScalingFunction(Color c) : ScalingFunction(c) { }
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KRPPKRPScalingFunction::KRPPKRPScalingFunction(Color c) : ScalingFunction(c) { }
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KPsKScalingFunction::KPsKScalingFunction(Color c) : ScalingFunction(c) { }
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KBPKBScalingFunction::KBPKBScalingFunction(Color c) : ScalingFunction(c) { }
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KBPKNScalingFunction::KBPKNScalingFunction(Color c) : ScalingFunction(c) { }
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KNPKScalingFunction::KNPKScalingFunction(Color c) : ScalingFunction(c) { }
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KPKPScalingFunction::KPKPScalingFunction(Color c) : ScalingFunction(c) { }
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/// Mate with KX vs K. This function is used to evaluate positions with
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/// King and plenty of material vs a lone king. It simply gives the
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/// attacking side a bonus for driving the defending king towards the edge
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/// of the board, and for keeping the distance between the two kings small.
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Value KXKEvaluationFunction::apply(const Position &pos) {
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assert(pos.non_pawn_material(weakerSide) == Value(0));
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assert(pos.pawn_count(weakerSide) == Value(0));
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Square winnerKSq = pos.king_square(strongerSide);
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Square loserKSq = pos.king_square(weakerSide);
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Value result =
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pos.non_pawn_material(strongerSide) +
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pos.pawn_count(strongerSide) * PawnValueEndgame +
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mate_table(loserKSq) +
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distance_bonus(square_distance(winnerKSq, loserKSq));
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if(pos.queen_count(strongerSide) > 0 || pos.rook_count(strongerSide) > 0 ||
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pos.bishop_count(strongerSide) > 1)
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// TODO: check for two equal-colored bishops!
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result += VALUE_KNOWN_WIN;
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return (strongerSide == pos.side_to_move())? result : -result;
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}
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/// Mate with KBN vs K. This is similar to KX vs K, but we have to drive the
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/// defending king towards a corner square of the right color.
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Value KBNKEvaluationFunction::apply(const Position &pos) {
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assert(pos.non_pawn_material(weakerSide) == Value(0));
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assert(pos.pawn_count(weakerSide) == Value(0));
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assert(pos.non_pawn_material(strongerSide) ==
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KnightValueMidgame + BishopValueMidgame);
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assert(pos.bishop_count(strongerSide) == 1);
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assert(pos.knight_count(strongerSide) == 1);
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assert(pos.pawn_count(strongerSide) == 0);
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Square winnerKSq = pos.king_square(strongerSide);
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Square loserKSq = pos.king_square(weakerSide);
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Square bishopSquare = pos.bishop_list(strongerSide, 0);
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if(square_color(bishopSquare) == BLACK) {
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winnerKSq = flop_square(winnerKSq);
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loserKSq = flop_square(loserKSq);
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}
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Value result =
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VALUE_KNOWN_WIN + distance_bonus(square_distance(winnerKSq, loserKSq)) +
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kbnk_mate_table(loserKSq);
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return (strongerSide == pos.side_to_move())? result : -result;
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}
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/// KP vs K. This endgame is evaluated with the help of a bitbase.
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Value KPKEvaluationFunction::apply(const Position &pos) {
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assert(pos.non_pawn_material(strongerSide) == Value(0));
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assert(pos.non_pawn_material(weakerSide) == Value(0));
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assert(pos.pawn_count(strongerSide) == 1);
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assert(pos.pawn_count(weakerSide) == 0);
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Square wksq, bksq, wpsq;
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Color stm;
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if(strongerSide == WHITE) {
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wksq = pos.king_square(WHITE);
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bksq = pos.king_square(BLACK);
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wpsq = pos.pawn_list(WHITE, 0);
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stm = pos.side_to_move();
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}
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else {
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wksq = flip_square(pos.king_square(BLACK));
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bksq = flip_square(pos.king_square(WHITE));
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wpsq = flip_square(pos.pawn_list(BLACK, 0));
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stm = opposite_color(pos.side_to_move());
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}
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if(square_file(wpsq) >= FILE_E) {
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wksq = flop_square(wksq);
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bksq = flop_square(bksq);
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wpsq = flop_square(wpsq);
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}
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if(probe_kpk(wksq, wpsq, bksq, stm)) {
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Value result =
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VALUE_KNOWN_WIN + PawnValueEndgame + Value(square_rank(wpsq));
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return (strongerSide == pos.side_to_move())? result : -result;
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}
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return VALUE_DRAW;
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}
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/// KR vs KP. This is a somewhat tricky endgame to evaluate precisely without
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/// a bitbase. The function below returns drawish scores when the pawn is
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/// far advanced with support of the king, while the attacking king is far
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/// away.
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Value KRKPEvaluationFunction::apply(const Position &pos) {
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assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
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assert(pos.pawn_count(strongerSide) == 0);
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assert(pos.non_pawn_material(weakerSide) == 0);
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assert(pos.pawn_count(weakerSide) == 1);
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Square wksq, wrsq, bksq, bpsq;
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int tempo = (pos.side_to_move() == strongerSide);
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wksq = pos.king_square(strongerSide);
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wrsq = pos.rook_list(strongerSide, 0);
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bksq = pos.king_square(weakerSide);
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bpsq = pos.pawn_list(weakerSide, 0);
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if(strongerSide == BLACK) {
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wksq = flip_square(wksq);
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wrsq = flip_square(wrsq);
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bksq = flip_square(bksq);
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bpsq = flip_square(bpsq);
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}
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Square queeningSq = make_square(square_file(bpsq), RANK_1);
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Value result;
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// If the stronger side's king is in front of the pawn, it's a win:
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if(wksq < bpsq && square_file(wksq) == square_file(bpsq))
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result = RookValueEndgame - Value(square_distance(wksq, bpsq));
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// If the weaker side's king is too far from the pawn and the rook,
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// it's a win:
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else if(square_distance(bksq, bpsq) - (tempo^1) >= 3 &&
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square_distance(bksq, wrsq) >= 3)
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result = RookValueEndgame - Value(square_distance(wksq, bpsq));
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// If the pawn is far advanced and supported by the defending king,
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// the position is drawish:
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else if(square_rank(bksq) <= RANK_3 && square_distance(bksq, bpsq) == 1 &&
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square_rank(wksq) >= RANK_4 &&
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square_distance(wksq, bpsq) - tempo > 2)
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result = Value(80 - square_distance(wksq, bpsq) * 8);
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else
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result = Value(200)
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- Value(square_distance(wksq, bpsq + DELTA_S) * 8)
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+ Value(square_distance(bksq, bpsq + DELTA_S) * 8)
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+ Value(square_distance(bpsq, queeningSq) * 8);
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return (strongerSide == pos.side_to_move())? result : -result;
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}
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/// KR vs KB. This is very simple, and always returns drawish scores. The
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/// score is slightly bigger when the defending king is close to the edge.
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Value KRKBEvaluationFunction::apply(const Position &pos) {
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assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
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assert(pos.pawn_count(strongerSide) == 0);
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assert(pos.non_pawn_material(weakerSide) == BishopValueMidgame);
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assert(pos.pawn_count(weakerSide) == 0);
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assert(pos.bishop_count(weakerSide) == 1);
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Value result = mate_table(pos.king_square(weakerSide));
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return (pos.side_to_move() == strongerSide)? result : -result;
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}
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/// KR vs KN. The attacking side has slightly better winning chances than
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/// in KR vs KB, particularly if the king and the knight are far apart.
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Value KRKNEvaluationFunction::apply(const Position &pos) {
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assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
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assert(pos.pawn_count(strongerSide) == 0);
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assert(pos.non_pawn_material(weakerSide) == KnightValueMidgame);
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assert(pos.pawn_count(weakerSide) == 0);
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assert(pos.knight_count(weakerSide) == 1);
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Square defendingKSq = pos.king_square(weakerSide);
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Square nSq = pos.knight_list(weakerSide, 0);
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Value result = Value(10) + mate_table(defendingKSq) +
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krkn_king_knight_distance_penalty(square_distance(defendingKSq, nSq));
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return (strongerSide == pos.side_to_move())? result : -result;
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}
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/// KQ vs KR. This is almost identical to KX vs K: We give the attacking
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/// king a bonus for having the kings close together, and for forcing the
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/// defending king towards the edge. If we also take care to avoid null move
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/// for the defending side in the search, this is usually sufficient to be
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/// able to win KQ vs KR.
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Value KQKREvaluationFunction::apply(const Position &pos) {
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assert(pos.non_pawn_material(strongerSide) == QueenValueMidgame);
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assert(pos.pawn_count(strongerSide) == 0);
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assert(pos.non_pawn_material(weakerSide) == RookValueMidgame);
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assert(pos.pawn_count(weakerSide) == 0);
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Square winnerKSq = pos.king_square(strongerSide);
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Square loserKSq = pos.king_square(weakerSide);
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Value result = QueenValueEndgame - RookValueEndgame +
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mate_table(loserKSq) + distance_bonus(square_distance(winnerKSq, loserKSq));
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return (strongerSide == pos.side_to_move())? result : -result;
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}
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/// KBPKScalingFunction scales endgames where the stronger side has king,
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/// bishop and one or more pawns. It checks for draws with rook pawns and a
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/// bishop of the wrong color. If such a draw is detected, ScaleFactor(0) is
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/// returned. If not, the return value is SCALE_FACTOR_NONE, i.e. no scaling
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/// will be used.
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ScaleFactor KBPKScalingFunction::apply(const Position &pos) {
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assert(pos.non_pawn_material(strongerSide) == BishopValueMidgame);
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assert(pos.bishop_count(strongerSide) == 1);
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assert(pos.pawn_count(strongerSide) >= 1);
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// No assertions about the material of weakerSide, because we want draws to
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// be detected even when the weaker side has some pawns.
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Bitboard pawns = pos.pawns(strongerSide);
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File pawnFile = square_file(pos.pawn_list(strongerSide, 0));
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if((pawnFile == FILE_A || pawnFile == FILE_H) &&
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(pawns & ~file_bb(pawnFile)) == EmptyBoardBB) {
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// All pawns are on a single rook file.
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Square bishopSq = pos.bishop_list(strongerSide, 0);
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Square queeningSq =
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relative_square(strongerSide, make_square(pawnFile, RANK_8));
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Square kingSq = pos.king_square(weakerSide);
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if(square_color(queeningSq) != square_color(bishopSq) &&
|
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file_distance(square_file(kingSq), pawnFile) <= 1) {
|
|
// The bishop has the wrong color, and the defending king is on the
|
|
// file of the pawn(s) or the neighboring file. Find the rank of the
|
|
// frontmost pawn:
|
|
|
|
Rank rank;
|
|
if(strongerSide == WHITE) {
|
|
for(rank = RANK_7; (rank_bb(rank) & pawns) == EmptyBoardBB; rank--);
|
|
assert(rank >= RANK_2 && rank <= RANK_7);
|
|
}
|
|
else {
|
|
for(rank = RANK_2; (rank_bb(rank) & pawns) == EmptyBoardBB; rank++);
|
|
rank = Rank(rank^7); // HACK
|
|
assert(rank >= RANK_2 && rank <= RANK_7);
|
|
}
|
|
// If the defending king has distance 1 to the promotion square or
|
|
// is placed somewhere in front of the pawn, it's a draw.
|
|
if(square_distance(kingSq, queeningSq) <= 1 ||
|
|
pawn_rank(strongerSide, kingSq) >= rank)
|
|
return ScaleFactor(0);
|
|
}
|
|
}
|
|
return SCALE_FACTOR_NONE;
|
|
}
|
|
|
|
|
|
/// KQKRPScalingFunction scales endgames where the stronger side has only
|
|
/// king and queen, while the weaker side has at least a rook and a pawn.
|
|
/// It tests for fortress draws with a rook on the third rank defended by
|
|
/// a pawn.
|
|
|
|
ScaleFactor KQKRPScalingFunction::apply(const Position &pos) {
|
|
assert(pos.non_pawn_material(strongerSide) == QueenValueMidgame);
|
|
assert(pos.queen_count(strongerSide) == 1);
|
|
assert(pos.pawn_count(strongerSide) == 0);
|
|
assert(pos.rook_count(weakerSide) == 1);
|
|
assert(pos.pawn_count(weakerSide) >= 1);
|
|
|
|
Square kingSq = pos.king_square(weakerSide);
|
|
if(pawn_rank(weakerSide, kingSq) <= RANK_2 &&
|
|
pawn_rank(weakerSide, pos.king_square(strongerSide)) >= RANK_4 &&
|
|
(pos.rooks(weakerSide) & relative_rank_bb(weakerSide, RANK_3)) &&
|
|
(pos.pawns(weakerSide) & relative_rank_bb(weakerSide, RANK_2)) &&
|
|
(pos.king_attacks(kingSq) & pos.pawns(weakerSide))) {
|
|
Square rsq = pos.rook_list(weakerSide, 0);
|
|
if(pos.pawn_attacks(strongerSide, rsq) & pos.pawns(weakerSide))
|
|
return ScaleFactor(0);
|
|
}
|
|
return SCALE_FACTOR_NONE;
|
|
}
|
|
|
|
|
|
/// KRPKRScalingFunction scales KRP vs KR endgames. This function knows a
|
|
/// handful of the most important classes of drawn positions, but is far
|
|
/// from perfect. It would probably be a good idea to add more knowledge
|
|
/// in the future.
|
|
///
|
|
/// It would also be nice to rewrite the actual code for this function,
|
|
/// which is mostly copied from Glaurung 1.x, and not very pretty.
|
|
|
|
ScaleFactor KRPKRScalingFunction::apply(const Position &pos) {
|
|
assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
|
|
assert(pos.pawn_count(strongerSide) == 1);
|
|
assert(pos.non_pawn_material(weakerSide) == RookValueMidgame);
|
|
assert(pos.pawn_count(weakerSide) == 0);
|
|
|
|
Square wksq = pos.king_square(strongerSide);
|
|
Square wrsq = pos.rook_list(strongerSide, 0);
|
|
Square wpsq = pos.pawn_list(strongerSide, 0);
|
|
Square bksq = pos.king_square(weakerSide);
|
|
Square brsq = pos.rook_list(weakerSide, 0);
|
|
|
|
// Orient the board in such a way that the stronger side is white, and the
|
|
// pawn is on the left half of the board:
|
|
if(strongerSide == BLACK) {
|
|
wksq = flip_square(wksq);
|
|
wrsq = flip_square(wrsq);
|
|
wpsq = flip_square(wpsq);
|
|
bksq = flip_square(bksq);
|
|
brsq = flip_square(brsq);
|
|
}
|
|
if(square_file(wpsq) > FILE_D) {
|
|
wksq = flop_square(wksq);
|
|
wrsq = flop_square(wrsq);
|
|
wpsq = flop_square(wpsq);
|
|
bksq = flop_square(bksq);
|
|
brsq = flop_square(brsq);
|
|
}
|
|
|
|
File f = square_file(wpsq);
|
|
Rank r = square_rank(wpsq);
|
|
Square queeningSq = make_square(f, RANK_8);
|
|
int tempo = (pos.side_to_move() == strongerSide);
|
|
|
|
// If the pawn is not too far advanced and the defending king defends the
|
|
// queening square, use the third-rank defence:
|
|
if(r <= RANK_5 && square_distance(bksq, queeningSq) <= 1 && wksq <= SQ_H5 &&
|
|
(square_rank(brsq) == RANK_6 || (r <= RANK_3 &&
|
|
square_rank(wrsq) != RANK_6)))
|
|
return ScaleFactor(0);
|
|
|
|
// The defending side saves a draw by checking from behind in case the pawn
|
|
// has advanced to the 6th rank with the king behind.
|
|
if(r == RANK_6 && square_distance(bksq, queeningSq) <= 1 &&
|
|
square_rank(wksq) + tempo <= RANK_6 &&
|
|
(square_rank(brsq) == RANK_1 ||
|
|
(!tempo && abs(square_file(brsq) - f) >= 3)))
|
|
return ScaleFactor(0);
|
|
|
|
if(r >= RANK_6 && bksq == queeningSq && square_rank(brsq) == RANK_1 &&
|
|
(!tempo || square_distance(wksq, wpsq) >= 2))
|
|
return ScaleFactor(0);
|
|
|
|
// White pawn on a7 and rook on a8 is a draw if black's king is on g7 or h7
|
|
// and the black rook is behind the pawn.
|
|
if(wpsq == SQ_A7 && wrsq == SQ_A8 && (bksq == SQ_H7 || bksq == SQ_G7) &&
|
|
square_file(brsq) == FILE_A &&
|
|
(square_rank(brsq) <= RANK_3 || square_file(wksq) >= FILE_D ||
|
|
square_rank(wksq) <= RANK_5))
|
|
return ScaleFactor(0);
|
|
|
|
// If the defending king blocks the pawn and the attacking king is too far
|
|
// away, it's a draw.
|
|
if(r <= RANK_5 && bksq == wpsq + DELTA_N &&
|
|
square_distance(wksq, wpsq) - tempo >= 2 &&
|
|
square_distance(wksq, brsq) - tempo >= 2)
|
|
return ScaleFactor(0);
|
|
|
|
// Pawn on the 7th rank supported by the rook from behind usually wins if the
|
|
// attacking king is closer to the queening square than the defending king,
|
|
// and the defending king cannot gain tempi by threatening the attacking
|
|
// rook.
|
|
if(r == RANK_7 && f != FILE_A && square_file(wrsq) == f
|
|
&& wrsq != queeningSq
|
|
&& (square_distance(wksq, queeningSq) <
|
|
square_distance(bksq, queeningSq) - 2 + tempo)
|
|
&& (square_distance(wksq, queeningSq) <
|
|
square_distance(bksq, wrsq) + tempo))
|
|
return ScaleFactor(SCALE_FACTOR_MAX
|
|
- 2 * square_distance(wksq, queeningSq));
|
|
|
|
// Similar to the above, but with the pawn further back:
|
|
if(f != FILE_A && square_file(wrsq) == f && wrsq < wpsq
|
|
&& (square_distance(wksq, queeningSq) <
|
|
square_distance(bksq, queeningSq) - 2 + tempo)
|
|
&& (square_distance(wksq, wpsq + DELTA_N) <
|
|
square_distance(bksq, wpsq + DELTA_N) - 2 + tempo)
|
|
&& (square_distance(bksq, wrsq) + tempo >= 3
|
|
|| (square_distance(wksq, queeningSq) <
|
|
square_distance(bksq, wrsq) + tempo
|
|
&& (square_distance(wksq, wpsq + DELTA_N) <
|
|
square_distance(bksq, wrsq) + tempo))))
|
|
return
|
|
ScaleFactor(SCALE_FACTOR_MAX
|
|
- (8 * square_distance(wpsq, queeningSq) +
|
|
2 * square_distance(wksq, queeningSq)));
|
|
|
|
return SCALE_FACTOR_NONE;
|
|
}
|
|
|
|
|
|
/// KRPPKRPScalingFunction scales KRPP vs KRP endgames. There is only a
|
|
/// single pattern: If the stronger side has no pawns and the defending king
|
|
/// is actively placed, the position is drawish.
|
|
|
|
ScaleFactor KRPPKRPScalingFunction::apply(const Position &pos) {
|
|
assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
|
|
assert(pos.pawn_count(strongerSide) == 2);
|
|
assert(pos.non_pawn_material(weakerSide) == RookValueMidgame);
|
|
assert(pos.pawn_count(weakerSide) == 1);
|
|
|
|
Square wpsq1 = pos.pawn_list(strongerSide, 0);
|
|
Square wpsq2 = pos.pawn_list(strongerSide, 1);
|
|
Square bksq = pos.king_square(weakerSide);
|
|
|
|
// Does the stronger side have a passed pawn?
|
|
if(pos.pawn_is_passed(strongerSide, wpsq1) ||
|
|
pos.pawn_is_passed(strongerSide, wpsq2))
|
|
return SCALE_FACTOR_NONE;
|
|
|
|
Rank r = Max(pawn_rank(strongerSide, wpsq1), pawn_rank(strongerSide, wpsq2));
|
|
|
|
if(file_distance(bksq, wpsq1) <= 1 && file_distance(bksq, wpsq2) <= 1
|
|
&& pawn_rank(strongerSide, bksq) > r) {
|
|
switch(r) {
|
|
|
|
case RANK_2: return ScaleFactor(10);
|
|
case RANK_3: return ScaleFactor(10);
|
|
case RANK_4: return ScaleFactor(15);
|
|
case RANK_5: return ScaleFactor(20);
|
|
case RANK_6: return ScaleFactor(40);
|
|
default: assert(false);
|
|
|
|
}
|
|
}
|
|
return SCALE_FACTOR_NONE;
|
|
}
|
|
|
|
|
|
/// KPsKScalingFunction scales endgames with king and two or more pawns
|
|
/// against king. There is just a single rule here: If all pawns are on
|
|
/// the same rook file and are blocked by the defending king, it's a draw.
|
|
|
|
ScaleFactor KPsKScalingFunction::apply(const Position &pos) {
|
|
assert(pos.non_pawn_material(strongerSide) == Value(0));
|
|
assert(pos.pawn_count(strongerSide) >= 2);
|
|
assert(pos.non_pawn_material(weakerSide) == Value(0));
|
|
assert(pos.pawn_count(weakerSide) == 0);
|
|
|
|
Bitboard pawns = pos.pawns(strongerSide);
|
|
|
|
// Are all pawns on the 'a' file?
|
|
if((pawns & ~FileABB) == EmptyBoardBB) {
|
|
// Does the defending king block the pawns?
|
|
Square ksq = pos.king_square(weakerSide);
|
|
if(square_distance(ksq, relative_square(strongerSide, SQ_A8)) <= 1)
|
|
return ScaleFactor(0);
|
|
else if(square_file(ksq) == FILE_A &&
|
|
(in_front_bb(strongerSide, ksq) & pawns) == EmptyBoardBB)
|
|
return ScaleFactor(0);
|
|
else
|
|
return SCALE_FACTOR_NONE;
|
|
}
|
|
// Are all pawns on the 'h' file?
|
|
else if((pawns & ~FileHBB) == EmptyBoardBB) {
|
|
// Does the defending king block the pawns?
|
|
Square ksq = pos.king_square(weakerSide);
|
|
if(square_distance(ksq, relative_square(strongerSide, SQ_H8)) <= 1)
|
|
return ScaleFactor(0);
|
|
else if(square_file(ksq) == FILE_H &&
|
|
(in_front_bb(strongerSide, ksq) & pawns) == EmptyBoardBB)
|
|
return ScaleFactor(0);
|
|
else
|
|
return SCALE_FACTOR_NONE;
|
|
}
|
|
else
|
|
return SCALE_FACTOR_NONE;
|
|
}
|
|
|
|
|
|
/// KBPKBScalingFunction scales KBP vs KB endgames. There are two rules:
|
|
/// If the defending king is somewhere along the path of the pawn, and the
|
|
/// square of the king is not of the same color as the stronger side's bishop,
|
|
/// it's a draw. If the two bishops have opposite color, it's almost always
|
|
/// a draw.
|
|
|
|
ScaleFactor KBPKBScalingFunction::apply(const Position &pos) {
|
|
assert(pos.non_pawn_material(strongerSide) == BishopValueMidgame);
|
|
assert(pos.bishop_count(strongerSide) == 1);
|
|
assert(pos.pawn_count(strongerSide) == 1);
|
|
assert(pos.non_pawn_material(weakerSide) == BishopValueMidgame);
|
|
assert(pos.bishop_count(weakerSide) == 1);
|
|
assert(pos.pawn_count(weakerSide) == 0);
|
|
|
|
Square pawnSq = pos.pawn_list(strongerSide, 0);
|
|
Square strongerBishopSq = pos.bishop_list(strongerSide, 0);
|
|
Square weakerBishopSq = pos.bishop_list(weakerSide, 0);
|
|
Square weakerKingSq = pos.king_square(weakerSide);
|
|
|
|
// Case 1: Defending king blocks the pawn, and cannot be driven away.
|
|
if(square_file(weakerKingSq) == square_file(pawnSq)
|
|
&& pawn_rank(strongerSide, pawnSq) < pawn_rank(strongerSide, weakerKingSq)
|
|
&& (square_color(weakerKingSq) != square_color(strongerBishopSq)
|
|
|| pawn_rank(strongerSide, weakerKingSq) <= RANK_6))
|
|
return ScaleFactor(0);
|
|
|
|
// Case 2: Opposite colored bishops.
|
|
if(square_color(strongerBishopSq) != square_color(weakerBishopSq)) {
|
|
|
|
// We assume that the position is drawn in the following three situations:
|
|
//
|
|
// a. The pawn is on rank 5 or further back.
|
|
// b. The defending king is somewhere in the pawn's path.
|
|
// c. The defending bishop attacks some square along the pawn's path,
|
|
// and is at least three squares away from the pawn.
|
|
//
|
|
// These rules are probably not perfect, but in practice they work
|
|
// reasonably well.
|
|
|
|
if(pawn_rank(strongerSide, pawnSq) <= RANK_5)
|
|
return ScaleFactor(0);
|
|
else {
|
|
Bitboard ray =
|
|
ray_bb(pawnSq, (strongerSide == WHITE)? SIGNED_DIR_N : SIGNED_DIR_S);
|
|
if(ray & pos.kings(weakerSide))
|
|
return ScaleFactor(0);
|
|
if((pos.bishop_attacks(weakerBishopSq) & ray)
|
|
&& square_distance(weakerBishopSq, pawnSq) >= 3)
|
|
return ScaleFactor(0);
|
|
}
|
|
}
|
|
return SCALE_FACTOR_NONE;
|
|
}
|
|
|
|
|
|
/// KBPKNScalingFunction scales KBP vs KN endgames. There is a single rule:
|
|
/// If the defending king is somewhere along the path of the pawn, and the
|
|
/// square of the king is not of the same color as the stronger side's bishop,
|
|
/// it's a draw.
|
|
|
|
ScaleFactor KBPKNScalingFunction::apply(const Position &pos) {
|
|
assert(pos.non_pawn_material(strongerSide) == BishopValueMidgame);
|
|
assert(pos.bishop_count(strongerSide) == 1);
|
|
assert(pos.pawn_count(strongerSide) == 1);
|
|
assert(pos.non_pawn_material(weakerSide) == KnightValueMidgame);
|
|
assert(pos.knight_count(weakerSide) == 1);
|
|
assert(pos.pawn_count(weakerSide) == 0);
|
|
|
|
Square pawnSq = pos.pawn_list(strongerSide, 0);
|
|
Square strongerBishopSq = pos.bishop_list(strongerSide, 0);
|
|
Square weakerKingSq = pos.king_square(weakerSide);
|
|
|
|
if(square_file(weakerKingSq) == square_file(pawnSq)
|
|
&& pawn_rank(strongerSide, pawnSq) < pawn_rank(strongerSide, weakerKingSq)
|
|
&& (square_color(weakerKingSq) != square_color(strongerBishopSq)
|
|
|| pawn_rank(strongerSide, weakerKingSq) <= RANK_6))
|
|
return ScaleFactor(0);
|
|
|
|
return SCALE_FACTOR_NONE;
|
|
}
|
|
|
|
|
|
/// KNPKScalingFunction scales KNP vs K endgames. There is a single rule:
|
|
/// If the pawn is a rook pawn on the 7th rank and the defending king prevents
|
|
/// the pawn from advancing, the position is drawn.
|
|
|
|
ScaleFactor KNPKScalingFunction::apply(const Position &pos) {
|
|
assert(pos.non_pawn_material(strongerSide) == KnightValueMidgame);
|
|
assert(pos.knight_count(strongerSide) == 1);
|
|
assert(pos.pawn_count(strongerSide) == 1);
|
|
assert(pos.non_pawn_material(weakerSide) == Value(0));
|
|
assert(pos.pawn_count(weakerSide) == 0);
|
|
|
|
Square pawnSq = pos.pawn_list(strongerSide, 0);
|
|
Square weakerKingSq = pos.king_square(weakerSide);
|
|
|
|
if(pawnSq == relative_square(strongerSide, SQ_A7) &&
|
|
square_distance(weakerKingSq, relative_square(strongerSide, SQ_A8)) <= 1)
|
|
return ScaleFactor(0);
|
|
|
|
if(pawnSq == relative_square(strongerSide, SQ_H7) &&
|
|
square_distance(weakerKingSq, relative_square(strongerSide, SQ_H8)) <= 1)
|
|
return ScaleFactor(0);
|
|
|
|
return SCALE_FACTOR_NONE;
|
|
}
|
|
|
|
|
|
/// KPKPScalingFunction scales KP vs KP endgames. This is done by removing
|
|
/// the weakest side's pawn and probing the KP vs K bitbase: If the weakest
|
|
/// side has a draw without the pawn, she probably has at least a draw with
|
|
/// the pawn as well. The exception is when the stronger side's pawn is far
|
|
/// advanced and not on a rook file; in this case it is often possible to win
|
|
/// (e.g. 8/4k3/3p4/3P4/6K1/8/8/8 w - - 0 1).
|
|
|
|
ScaleFactor KPKPScalingFunction::apply(const Position &pos) {
|
|
assert(pos.non_pawn_material(strongerSide) == Value(0));
|
|
assert(pos.non_pawn_material(weakerSide) == Value(0));
|
|
assert(pos.pawn_count(WHITE) == 1);
|
|
assert(pos.pawn_count(BLACK) == 1);
|
|
|
|
Square wksq, bksq, wpsq;
|
|
Color stm;
|
|
|
|
if(strongerSide == WHITE) {
|
|
wksq = pos.king_square(WHITE);
|
|
bksq = pos.king_square(BLACK);
|
|
wpsq = pos.pawn_list(WHITE, 0);
|
|
stm = pos.side_to_move();
|
|
}
|
|
else {
|
|
wksq = flip_square(pos.king_square(BLACK));
|
|
bksq = flip_square(pos.king_square(WHITE));
|
|
wpsq = flip_square(pos.pawn_list(BLACK, 0));
|
|
stm = opposite_color(pos.side_to_move());
|
|
}
|
|
|
|
if(square_file(wpsq) >= FILE_E) {
|
|
wksq = flop_square(wksq);
|
|
bksq = flop_square(bksq);
|
|
wpsq = flop_square(wpsq);
|
|
}
|
|
|
|
// If the pawn has advanced to the fifth rank or further, and is not a
|
|
// rook pawn, it's too dangerous to assume that it's at least a draw.
|
|
if(square_rank(wpsq) >= RANK_5 && square_file(wpsq) != FILE_A)
|
|
return SCALE_FACTOR_NONE;
|
|
|
|
// Probe the KPK bitbase with the weakest side's pawn removed. If it's a
|
|
// draw, it's probably at least a draw even with the pawn.
|
|
if(probe_kpk(wksq, wpsq, bksq, stm))
|
|
return SCALE_FACTOR_NONE;
|
|
else
|
|
return ScaleFactor(0);
|
|
}
|
|
|
|
|
|
/// init_bitbases() is called during program initialization, and simply loads
|
|
/// bitbases from disk into memory. At the moment, there is only the bitbase
|
|
/// for KP vs K, but we may decide to add other bitbases later.
|
|
|
|
void init_bitbases() {
|
|
generate_kpk_bitbase(KPKBitbase);
|
|
}
|
|
|
|
|
|
namespace {
|
|
|
|
// Probe the KP vs K bitbase:
|
|
|
|
int probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
|
|
int wp = int(square_file(wpsq)) + (int(square_rank(wpsq)) - 1) * 4;
|
|
int index = int(stm) + 2*int(bksq) + 128*int(wksq) + 8192*wp;
|
|
|
|
assert(index >= 0 && index < 24576*8);
|
|
return KPKBitbase[index/8] & (1 << (index&7));
|
|
}
|
|
|
|
}
|