mirror of
https://github.com/sockspls/badfish
synced 2025-04-30 00:33:09 +00:00
2adbb80b8b
Also heavy cleanup while there. No functional change. Signed-off-by: Marco Costalba <mcostalba@gmail.com>
320 lines
7.9 KiB
C++
320 lines
7.9 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
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Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
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Stockfish 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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Stockfish 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 "bitboard.h"
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#include "square.h"
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////
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//// Local definitions
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////
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namespace {
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enum Result {
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RESULT_UNKNOWN,
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RESULT_INVALID,
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RESULT_WIN,
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RESULT_LOSS,
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RESULT_DRAW
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};
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struct KPKPosition {
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void from_index(int index);
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bool is_legal() const;
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bool is_immediate_draw() const;
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bool is_immediate_win() const;
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Bitboard wk_attacks() const { return StepAttackBB[WK][whiteKingSquare]; }
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Bitboard bk_attacks() const { return StepAttackBB[BK][blackKingSquare]; }
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Bitboard pawn_attacks() const { return StepAttackBB[WP][pawnSquare]; }
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Square whiteKingSquare, blackKingSquare, pawnSquare;
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Color sideToMove;
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};
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const int IndexMax = 2 * 24 * 64 * 64;
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Result classify_wtm(const KPKPosition& pos, const Result bb[]);
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Result classify_btm(const KPKPosition& pos, const Result bb[]);
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int compute_index(Square wksq, Square bksq, Square psq, Color stm);
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}
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////
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//// Functions
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////
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void generate_kpk_bitbase(uint8_t bitbase[]) {
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bool repeat;
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int i, j, b;
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KPKPosition pos;
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Result bb[IndexMax];
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// Initialize table
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for (i = 0; i < IndexMax; i++)
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{
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pos.from_index(i);
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bb[i] = !pos.is_legal() ? RESULT_INVALID
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: pos.is_immediate_draw() ? RESULT_DRAW
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: pos.is_immediate_win() ? RESULT_WIN : RESULT_UNKNOWN;
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}
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// Iterate until all positions are classified (30 cycles needed)
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do {
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repeat = false;
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for (i = 0; i < IndexMax; i++)
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if (bb[i] == RESULT_UNKNOWN)
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{
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pos.from_index(i);
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bb[i] = (pos.sideToMove == WHITE) ? classify_wtm(pos, bb)
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: classify_btm(pos, bb);
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if (bb[i] != RESULT_UNKNOWN)
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repeat = true;
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}
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} while (repeat);
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// Compress result and map into supplied bitbase parameter
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for (i = 0; i < 24576; i++)
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{
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b = 0;
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for (j = 0; j < 8; j++)
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if (bb[8*i+j] == RESULT_WIN || bb[8*i+j] == RESULT_LOSS)
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b |= (1 << j);
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bitbase[i] = (uint8_t)b;
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}
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}
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namespace {
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int compute_index(Square wksq, Square bksq, Square psq, Color stm) {
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int p = int(square_file(psq)) + (int(square_rank(psq)) - 1) * 4;
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int r = int(stm) + 2 * int(bksq) + 128 * int(wksq) + 8192 * p;
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assert(r >= 0 && r < IndexMax);
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return r;
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}
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void KPKPosition::from_index(int index) {
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int s = (index / 8192) % 24;
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sideToMove = Color(index % 2);
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blackKingSquare = Square((index / 2) % 64);
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whiteKingSquare = Square((index / 128) % 64);
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pawnSquare = make_square(File(s % 4), Rank(s / 4 + 1));
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}
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bool KPKPosition::is_legal() const {
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if ( whiteKingSquare == pawnSquare
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|| whiteKingSquare == blackKingSquare
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|| pawnSquare == blackKingSquare)
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return false;
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if (sideToMove == WHITE)
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{
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if ( bit_is_set(wk_attacks(), blackKingSquare)
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|| bit_is_set(pawn_attacks(), blackKingSquare))
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return false;
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}
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else if (bit_is_set(bk_attacks(), whiteKingSquare))
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return false;
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return true;
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}
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bool KPKPosition::is_immediate_draw() const {
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if (sideToMove == BLACK)
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{
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Bitboard wka = wk_attacks();
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Bitboard bka = bk_attacks();
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// Case 1: Stalemate
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if ((bka & ~(wka | pawn_attacks())) == EmptyBoardBB)
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return true;
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// Case 2: King can capture pawn
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if (bit_is_set(bka, pawnSquare) && !bit_is_set(wka, pawnSquare))
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return true;
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}
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else
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{
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// Case 1: Stalemate
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if ( whiteKingSquare == SQ_A8
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&& pawnSquare == SQ_A7
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&& (blackKingSquare == SQ_C7 || blackKingSquare == SQ_C8))
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return true;
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}
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return false;
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}
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bool KPKPosition::is_immediate_win() const {
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// The position is an immediate win if it is white to move and the
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// white pawn can be promoted without getting captured.
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return sideToMove == WHITE
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&& square_rank(pawnSquare) == RANK_7
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&& ( square_distance(blackKingSquare, pawnSquare + DELTA_N) > 1
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|| bit_is_set(wk_attacks(), pawnSquare + DELTA_N));
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}
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Result classify_wtm(const KPKPosition& pos, const Result bb[]) {
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// If one move leads to a position classified as RESULT_LOSS, the result
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// of the current position is RESULT_WIN. If all moves lead to positions
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// classified as RESULT_DRAW, the current position is classified RESULT_DRAW
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// otherwise the current position is classified as RESULT_UNKNOWN.
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bool unknownFound = false;
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Bitboard b;
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Square s;
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int idx;
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// King moves
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b = pos.wk_attacks();
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while (b)
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{
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s = pop_1st_bit(&b);
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idx = compute_index(s, pos.blackKingSquare, pos.pawnSquare, BLACK);
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switch (bb[idx]) {
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case RESULT_LOSS:
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return RESULT_WIN;
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case RESULT_UNKNOWN:
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unknownFound = true;
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case RESULT_DRAW:
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case RESULT_INVALID:
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break;
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default:
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assert(false);
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}
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}
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// Pawn moves
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if (square_rank(pos.pawnSquare) < RANK_7)
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{
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s = pos.pawnSquare + DELTA_N;
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idx = compute_index(pos.whiteKingSquare, pos.blackKingSquare, s, BLACK);
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switch (bb[idx]) {
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case RESULT_LOSS:
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return RESULT_WIN;
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case RESULT_UNKNOWN:
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unknownFound = true;
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case RESULT_DRAW:
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case RESULT_INVALID:
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break;
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default:
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assert(false);
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}
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// Double pawn push
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if ( square_rank(s) == RANK_3
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&& s != pos.whiteKingSquare
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&& s != pos.blackKingSquare)
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{
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s += DELTA_N;
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idx = compute_index(pos.whiteKingSquare, pos.blackKingSquare, s, BLACK);
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switch (bb[idx]) {
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case RESULT_LOSS:
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return RESULT_WIN;
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case RESULT_UNKNOWN:
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unknownFound = true;
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case RESULT_DRAW:
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case RESULT_INVALID:
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break;
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default:
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assert(false);
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}
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}
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}
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return unknownFound ? RESULT_UNKNOWN : RESULT_DRAW;
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}
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Result classify_btm(const KPKPosition& pos, const Result bb[]) {
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// If one move leads to a position classified as RESULT_DRAW, the result
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// of the current position is RESULT_DRAW. If all moves lead to positions
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// classified as RESULT_WIN, the current position is classified as
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// RESULT_LOSS. Otherwise, the current position is classified as
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// RESULT_UNKNOWN.
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bool unknownFound = false;
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Bitboard b;
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Square s;
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int idx;
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// King moves
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b = pos.bk_attacks();
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while (b)
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{
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s = pop_1st_bit(&b);
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idx = compute_index(pos.whiteKingSquare, s, pos.pawnSquare, WHITE);
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switch (bb[idx]) {
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case RESULT_DRAW:
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return RESULT_DRAW;
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case RESULT_UNKNOWN:
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unknownFound = true;
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case RESULT_WIN:
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case RESULT_INVALID:
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break;
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default:
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assert(false);
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}
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}
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return unknownFound ? RESULT_UNKNOWN : RESULT_LOSS;
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}
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}
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