+++ /dev/null
-/*
- Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
- Copyright (C) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
-
- Stockfish is free software: you can redistribute it and/or modify
- it under the terms of the GNU General Public License as published by
- the Free Software Foundation, either version 3 of the License, or
- (at your option) any later version.
-
- Stockfish is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- GNU General Public License for more details.
-
- You should have received a copy of the GNU General Public License
- along with this program. If not, see <http://www.gnu.org/licenses/>.
-*/
-
-#include <cassert>
-#include <numeric>
-#include <vector>
-
-#include "bitboard.h"
-#include "types.h"
-
-namespace {
-
- // There are 24 possible pawn squares: files A to D and ranks from 2 to 7.
- // Positions with the pawn on files E to H will be mirrored before probing.
- constexpr unsigned MAX_INDEX = 2*24*64*64; // stm * psq * wksq * bksq = 196608
-
- // Each uint32_t stores results of 32 positions, one per bit
- uint32_t KPKBitbase[MAX_INDEX / 32];
-
- // A KPK bitbase index is an integer in [0, IndexMax] range
- //
- // Information is mapped in a way that minimizes the number of iterations:
- //
- // bit 0- 5: white king square (from SQ_A1 to SQ_H8)
- // bit 6-11: black king square (from SQ_A1 to SQ_H8)
- // bit 12: side to move (WHITE or BLACK)
- // bit 13-14: white pawn file (from FILE_A to FILE_D)
- // bit 15-17: white pawn RANK_7 - rank (from RANK_7 - RANK_7 to RANK_7 - RANK_2)
- unsigned index(Color us, Square bksq, Square wksq, Square psq) {
- return int(wksq) | (bksq << 6) | (us << 12) | (file_of(psq) << 13) | ((RANK_7 - rank_of(psq)) << 15);
- }
-
- enum Result {
- INVALID = 0,
- UNKNOWN = 1,
- DRAW = 2,
- WIN = 4
- };
-
- Result& operator|=(Result& r, Result v) { return r = Result(r | v); }
-
- struct KPKPosition {
- KPKPosition() = default;
- explicit KPKPosition(unsigned idx);
- operator Result() const { return result; }
- Result classify(const std::vector<KPKPosition>& db)
- { return us == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
-
- template<Color Us> Result classify(const std::vector<KPKPosition>& db);
-
- Color us;
- Square ksq[COLOR_NB], psq;
- Result result;
- };
-
-} // namespace
-
-
-bool Bitbases::probe(Square wksq, Square wpsq, Square bksq, Color us) {
-
- assert(file_of(wpsq) <= FILE_D);
-
- unsigned idx = index(us, bksq, wksq, wpsq);
- return KPKBitbase[idx / 32] & (1 << (idx & 0x1F));
-}
-
-
-void Bitbases::init() {
-
- std::vector<KPKPosition> db(MAX_INDEX);
- unsigned idx, repeat = 1;
-
- // Initialize db with known win / draw positions
- for (idx = 0; idx < MAX_INDEX; ++idx)
- db[idx] = KPKPosition(idx);
-
- // Iterate through the positions until none of the unknown positions can be
- // changed to either wins or draws (15 cycles needed).
- while (repeat)
- for (repeat = idx = 0; idx < MAX_INDEX; ++idx)
- repeat |= (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN);
-
- // Map 32 results into one KPKBitbase[] entry
- for (idx = 0; idx < MAX_INDEX; ++idx)
- if (db[idx] == WIN)
- KPKBitbase[idx / 32] |= 1 << (idx & 0x1F);
-}
-
-
-namespace {
-
- KPKPosition::KPKPosition(unsigned idx) {
-
- ksq[WHITE] = Square((idx >> 0) & 0x3F);
- ksq[BLACK] = Square((idx >> 6) & 0x3F);
- us = Color ((idx >> 12) & 0x01);
- psq = make_square(File((idx >> 13) & 0x3), Rank(RANK_7 - ((idx >> 15) & 0x7)));
-
- // Check if two pieces are on the same square or if a king can be captured
- if ( distance(ksq[WHITE], ksq[BLACK]) <= 1
- || ksq[WHITE] == psq
- || ksq[BLACK] == psq
- || (us == WHITE && (PawnAttacks[WHITE][psq] & ksq[BLACK])))
- result = INVALID;
-
- // Immediate win if a pawn can be promoted without getting captured
- else if ( us == WHITE
- && rank_of(psq) == RANK_7
- && ksq[us] != psq + NORTH
- && ( distance(ksq[~us], psq + NORTH) > 1
- || (PseudoAttacks[KING][ksq[us]] & (psq + NORTH))))
- result = WIN;
-
- // Immediate draw if it is a stalemate or a king captures undefended pawn
- else if ( us == BLACK
- && ( !(PseudoAttacks[KING][ksq[us]] & ~(PseudoAttacks[KING][ksq[~us]] | PawnAttacks[~us][psq]))
- || (PseudoAttacks[KING][ksq[us]] & psq & ~PseudoAttacks[KING][ksq[~us]])))
- result = DRAW;
-
- // Position will be classified later
- else
- result = UNKNOWN;
- }
-
- template<Color Us>
- Result KPKPosition::classify(const std::vector<KPKPosition>& db) {
-
- // White to move: If one move leads to a position classified as WIN, the result
- // of the current position is WIN. If all moves lead to positions classified
- // as DRAW, the current position is classified as DRAW, otherwise the current
- // position is classified as UNKNOWN.
- //
- // Black to move: If one move leads to a position classified as DRAW, the result
- // of the current position is DRAW. If all moves lead to positions classified
- // as WIN, the position is classified as WIN, otherwise the current position is
- // classified as UNKNOWN.
-
- constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
- constexpr Result Good = (Us == WHITE ? WIN : DRAW);
- constexpr Result Bad = (Us == WHITE ? DRAW : WIN);
-
- Result r = INVALID;
- Bitboard b = PseudoAttacks[KING][ksq[Us]];
-
- while (b)
- r |= Us == WHITE ? db[index(Them, ksq[Them] , pop_lsb(&b), psq)]
- : db[index(Them, pop_lsb(&b), ksq[Them] , psq)];
-
- if (Us == WHITE)
- {
- if (rank_of(psq) < RANK_7) // Single push
- r |= db[index(Them, ksq[Them], ksq[Us], psq + NORTH)];
-
- if ( rank_of(psq) == RANK_2 // Double push
- && psq + NORTH != ksq[Us]
- && psq + NORTH != ksq[Them])
- r |= db[index(Them, ksq[Them], ksq[Us], psq + NORTH + NORTH)];
- }
-
- return result = r & Good ? Good : r & UNKNOWN ? UNKNOWN : Bad;
- }
-
-} // namespace
projects / stockfish / blobdiff