386 lines
11 KiB
C++
386 lines
11 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 "pawns.h"
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////
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//// Local definitions
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////
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namespace {
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/// Constants and variables
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// Doubled pawn penalty by file, middle game.
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const Value DoubledPawnMidgamePenalty[8] = {
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Value(20), Value(30), Value(34), Value(34),
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Value(34), Value(34), Value(30), Value(20)
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};
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// Doubled pawn penalty by file, endgame.
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const Value DoubledPawnEndgamePenalty[8] = {
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Value(35), Value(40), Value(40), Value(40),
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Value(40), Value(40), Value(40), Value(35)
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};
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// Isolated pawn penalty by file, middle game.
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const Value IsolatedPawnMidgamePenalty[8] = {
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Value(20), Value(30), Value(34), Value(34),
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Value(34), Value(34), Value(30), Value(20)
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};
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// Isolated pawn penalty by file, endgame.
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const Value IsolatedPawnEndgamePenalty[8] = {
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Value(35), Value(40), Value(40), Value(40),
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Value(40), Value(40), Value(40), Value(35)
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};
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// Backward pawn penalty by file, middle game.
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const Value BackwardPawnMidgamePenalty[8] = {
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Value(16), Value(24), Value(27), Value(27),
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Value(27), Value(27), Value(24), Value(16)
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};
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// Backward pawn penalty by file, endgame.
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const Value BackwardPawnEndgamePenalty[8] = {
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Value(28), Value(32), Value(32), Value(32),
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Value(32), Value(32), Value(32), Value(28)
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};
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// Pawn chain membership bonus by file, middle game.
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const Value ChainMidgameBonus[8] = {
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Value(14), Value(16), Value(17), Value(18),
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Value(18), Value(17), Value(16), Value(14)
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};
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// Pawn chain membership bonus by file, endgame.
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const Value ChainEndgameBonus[8] = {
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Value(16), Value(16), Value(16), Value(16),
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Value(16), Value(16), Value(16), Value(16)
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};
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// Candidate passed pawn bonus by rank, middle game.
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const Value CandidateMidgameBonus[8] = {
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Value(0), Value(12), Value(12), Value(20),
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Value(40), Value(90), Value(0), Value(0)
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};
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// Candidate passed pawn bonus by rank, endgame.
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const Value CandidateEndgameBonus[8] = {
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Value(0), Value(24), Value(24), Value(40),
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Value(80), Value(180), Value(0), Value(0)
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};
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// Evaluate pawn storms?
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const bool EvaluatePawnStorms = true;
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// Pawn storm tables for positions with opposite castling:
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const int QStormTable[64] = {
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0, 0, 0, 0, 0, 0, 0, 0,
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-22, -22, -22, -13, -4, 0, 0, 0,
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-4, -9, -9, -9, -4, 0, 0, 0,
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9, 18, 22, 18, 9, 0, 0, 0,
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22, 31, 31, 22, 0, 0, 0, 0,
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31, 40, 40, 31, 0, 0, 0, 0,
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31, 40, 40, 31, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0
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};
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const int KStormTable[64] = {
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0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, -4, -13, -22, -27, -27,
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0, 0, 0, -4, -9, -13, -18, -18,
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0, 0, 0, 0, 9, 9, 9, 9,
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0, 0, 0, 0, 9, 18, 27, 27,
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0, 0, 0, 0, 9, 27, 40, 36,
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0, 0, 0, 0, 0, 31, 40, 31,
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0, 0, 0, 0, 0, 0, 0, 0
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};
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// Pawn storm open file bonuses by file:
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const int KStormOpenFileBonus[8] = {
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45, 45, 30, 0, 0, 0, 0, 0
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};
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const int QStormOpenFileBonus[8] = {
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0, 0, 0, 0, 0, 30, 45, 30
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};
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}
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////
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//// Functions
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////
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/// Constructor
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PawnInfoTable::PawnInfoTable(unsigned numOfEntries) {
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size = numOfEntries;
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entries = new PawnInfo[size];
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if(entries == NULL) {
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std::cerr << "Failed to allocate " << (numOfEntries * sizeof(PawnInfo))
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<< " bytes for pawn hash table." << std::endl;
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exit(EXIT_FAILURE);
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}
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this->clear();
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}
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/// Destructor
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PawnInfoTable::~PawnInfoTable() {
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delete [] entries;
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}
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/// PawnInfoTable::clear() clears the pawn hash table by setting all
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/// entries to 0.
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void PawnInfoTable::clear() {
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memset(entries, 0, size * sizeof(PawnInfo));
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}
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/// PawnInfoTable::get_pawn_info() takes a position object as input, computes
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/// a PawnInfo object, and returns a pointer to it. The result is also
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/// stored in a hash table, so we don't have to recompute everything when
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/// the same pawn structure occurs again.
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PawnInfo *PawnInfoTable::get_pawn_info(const Position &pos) {
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assert(pos.is_ok());
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Key key = pos.get_pawn_key();
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int index = int(key & (size - 1));
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PawnInfo *pi = entries + index;
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// If pi->key matches the position's pawn hash key, it means that we
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// have analysed this pawn structure before, and we can simply return the
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// information we found the last time instead of recomputing it:
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if(pi->key == key)
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return pi;
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// Clear the PawnInfo object, and set the key:
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pi->clear();
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pi->key = key;
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Value mgValue[2] = {Value(0), Value(0)};
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Value egValue[2] = {Value(0), Value(0)};
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// Loop through the pawns for both colors:
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for(Color us = WHITE; us <= BLACK; us++) {
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Color them = opposite_color(us);
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Bitboard ourPawns = pos.pawns(us);
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Bitboard theirPawns = pos.pawns(them);
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Bitboard pawns = ourPawns;
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// Initialize pawn storm scores by giving bonuses for open files:
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if(EvaluatePawnStorms)
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for(File f = FILE_A; f <= FILE_H; f++)
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if(pos.file_is_half_open(us, f)) {
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pi->ksStormValue[us] += KStormOpenFileBonus[f];
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pi->qsStormValue[us] += QStormOpenFileBonus[f];
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}
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// Loop through all pawns of the current color and score each pawn:
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while(pawns) {
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Square s = pop_1st_bit(&pawns);
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File f = square_file(s);
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Rank r = square_rank(s);
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bool passed, doubled, isolated, backward, chain, candidate;
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int bonus;
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assert(pos.piece_on(s) == pawn_of_color(us));
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// The file containing the pawn is not half open:
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pi->halfOpenFiles[us] &= ~(1 << f);
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// Passed, isolated or doubled pawn?
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passed = pos.pawn_is_passed(us, s);
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isolated = pos.pawn_is_isolated(us, s);
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doubled = pos.pawn_is_doubled(us, s);
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if(EvaluatePawnStorms) {
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// We calculate kingside and queenside pawn storm
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// scores for both colors. These are used when evaluating
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// middle game positions with opposite side castling.
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//
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// Each pawn is given a base score given by a piece square table
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// (KStormTable[] or QStormTable[]). This score is increased if
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// there are enemy pawns on adjacent files in front of the pawn.
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// This is because we want to be able to open files against the
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// enemy king, and to avoid blocking the pawn structure (e.g. white
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// pawns on h6, g5, black pawns on h7, g6, f7).
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// Kingside pawn storms:
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bonus = KStormTable[relative_square(us, s)];
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if(bonus > 0 && outpost_mask(us, s) & theirPawns) {
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switch(f) {
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case FILE_F:
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bonus += bonus / 4;
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break;
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case FILE_G:
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bonus += bonus / 2 + bonus / 4;
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break;
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case FILE_H:
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bonus += bonus / 2;
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break;
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default:
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break;
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}
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}
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pi->ksStormValue[us] += bonus;
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// Queenside pawn storms:
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bonus = QStormTable[relative_square(us, s)];
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if(bonus > 0 && passed_pawn_mask(us, s) & theirPawns) {
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switch(f) {
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case FILE_A:
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bonus += bonus / 2;
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break;
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case FILE_B:
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bonus += bonus / 2 + bonus / 4;
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break;
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case FILE_C:
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bonus += bonus / 2;
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break;
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default:
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break;
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}
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}
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pi->qsStormValue[us] += bonus;
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}
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// Member of a pawn chain? We could speed up the test a little by
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// introducing an array of masks indexed by color and square for doing
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// the test, but because everything is hashed, it probably won't make
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// any noticable difference.
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chain = (us == WHITE)?
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(ourPawns & neighboring_files_bb(f) & (rank_bb(r) | rank_bb(r-1))) :
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(ourPawns & neighboring_files_bb(f) & (rank_bb(r) | rank_bb(r+1)));
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// Test for backward pawn.
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// If the pawn is isolated, passed, or member of a pawn chain, it cannot
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// be backward:
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if(passed || isolated || chain)
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backward = false;
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// If the pawn can capture an enemy pawn, it's not backward:
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else if(pos.pawn_attacks(us, s) & theirPawns)
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backward = false;
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// Check for friendly pawns behind on neighboring files:
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else if(ourPawns & in_front_bb(them, r) & neighboring_files_bb(f))
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backward = false;
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else {
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// We now know that there is no friendly pawns beside or behind this
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// pawn on neighboring files. We now check whether the pawn is
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// backward by looking in the forward direction on the neighboring
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// files, and seeing whether we meet a friendly or an enemy pawn first.
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Bitboard b;
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if(us == WHITE) {
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for(b=pos.pawn_attacks(us, s); !(b&(ourPawns|theirPawns)); b<<=8);
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backward = (b | (b << 8)) & theirPawns;
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}
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else {
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for(b=pos.pawn_attacks(us, s); !(b&(ourPawns|theirPawns)); b>>=8);
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backward = (b | (b >> 8)) & theirPawns;
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}
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}
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// Test for candidate passed pawn.
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candidate =
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(!passed && pos.file_is_half_open(them, f) &&
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count_1s_max_15(neighboring_files_bb(f)
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& (in_front_bb(them, r) | rank_bb(r))
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& ourPawns)
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- count_1s_max_15(neighboring_files_bb(f) & in_front_bb(us, r)
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& theirPawns)
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>= 0);
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// In order to prevent doubled passed pawns from receiving a too big
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// bonus, only the frontmost passed pawn on each file is considered as
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// a true passed pawn.
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if(passed && (ourPawns & squares_in_front_of(us, s))) {
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// candidate = true;
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passed = false;
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}
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// Score this pawn:
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Value mv = Value(0), ev = Value(0);
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if(isolated) {
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mv -= IsolatedPawnMidgamePenalty[f];
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ev -= IsolatedPawnEndgamePenalty[f];
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if(pos.file_is_half_open(them, f)) {
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mv -= IsolatedPawnMidgamePenalty[f] / 2;
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ev -= IsolatedPawnEndgamePenalty[f] / 2;
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}
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}
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if(doubled) {
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mv -= DoubledPawnMidgamePenalty[f];
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ev -= DoubledPawnEndgamePenalty[f];
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}
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if(backward) {
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mv -= BackwardPawnMidgamePenalty[f];
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ev -= BackwardPawnEndgamePenalty[f];
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if(pos.file_is_half_open(them, f)) {
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mv -= BackwardPawnMidgamePenalty[f] / 2;
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ev -= BackwardPawnEndgamePenalty[f] / 2;
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}
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}
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if(chain) {
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mv += ChainMidgameBonus[f];
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ev += ChainEndgameBonus[f];
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}
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if(candidate) {
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mv += CandidateMidgameBonus[pawn_rank(us, s)];
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ev += CandidateEndgameBonus[pawn_rank(us, s)];
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}
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mgValue[us] += mv;
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egValue[us] += ev;
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// If the pawn is passed, set the square of the pawn in the passedPawns
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// bitboard:
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if(passed)
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set_bit(&(pi->passedPawns), s);
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}
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}
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pi->mgValue = int16_t(mgValue[WHITE] - mgValue[BLACK]);
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pi->egValue = int16_t(egValue[WHITE] - egValue[BLACK]);
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return pi;
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}
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