+++ /dev/null
-/*
- Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, 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 <vector>
-
-#include "bitboard.h"
-#include "types.h"
-
-namespace {
-
- // The possible pawns squares are 24, the first 4 files and ranks from 2 to 7
- const unsigned IndexMax = 24*64*64*2; // wp_sq * wk_sq * bk_sq * stm = 196608
-
- // Each uint32_t stores results of 32 positions, one per bit
- uint32_t KPKBitbase[IndexMax / 32];
-
- // A KPK bitbase index is an integer in [0, IndexMax] range
- //
- // Information is mapped in this way
- //
- // bit 0: side to move (WHITE or BLACK)
- // bit 1- 6: black king square (from SQ_A1 to SQ_H8)
- // bit 7-12: white king square (from SQ_A1 to SQ_H8)
- // bit 13-14: white pawn file (from FILE_A to FILE_D)
- // bit 15-17: white pawn rank - 1 (from RANK_2 - 1 to RANK_7 - 1)
- unsigned index(Color stm, Square bksq, Square wksq, Square psq) {
- return stm + (bksq << 1) + (wksq << 7) + (file_of(psq) << 13) + ((rank_of(psq) - 1) << 15);
- }
-
- enum Result {
- INVALID = 0,
- UNKNOWN = 1,
- DRAW = 2,
- WIN = 4
- };
-
- inline Result& operator|=(Result& r, Result v) { return r = Result(r | v); }
-
- struct KPKPosition {
-
- void classify_leaf(unsigned idx);
-
- Result classify(const std::vector<KPKPosition>& db)
- { return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
-
- operator Result() const { return res; }
-
- private:
- template<Color Us> Bitboard k_attacks() const
- { return StepAttacksBB[KING][Us == WHITE ? wksq : bksq]; }
-
- template<Color Us> Result classify(const std::vector<KPKPosition>& db);
-
- Color stm;
- Square bksq, wksq, psq;
- Result res;
- };
-
-} // namespace
-
-
-bool Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
-
- assert(file_of(wpsq) <= FILE_D);
-
- unsigned idx = index(stm, bksq, wksq, wpsq);
- return KPKBitbase[idx / 32] & (1 << (idx & 31));
-}
-
-
-void Bitbases::init_kpk() {
-
- unsigned idx, repeat = 1;
- std::vector<KPKPosition> db(IndexMax);
-
- // Initialize db with known win / draw positions
- for (idx = 0; idx < IndexMax; idx++)
- db[idx].classify_leaf(idx);
-
- // Iterate until all positions are classified (30 cycles needed)
- while (repeat)
- for (repeat = idx = 0; idx < IndexMax; idx++)
- if (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN)
- repeat = 1;
-
- // Map 32 results into one KPKBitbase[] entry
- for (idx = 0; idx < IndexMax; idx++)
- if (db[idx] == WIN)
- KPKBitbase[idx / 32] |= 1 << (idx & 31);
-}
-
-
-namespace {
-
- void KPKPosition::classify_leaf(unsigned idx) {
-
- stm = Color(idx & 1);
- bksq = Square((idx >> 1) & 0x3F);
- wksq = Square((idx >> 7) & 0x3F);
- psq = File((idx >> 13) & 3) | Rank((idx >> 15) + 1);
-
- // Check if two pieces are on the same square or if a king can be captured
- if ( wksq == psq || wksq == bksq || bksq == psq
- || (k_attacks<WHITE>() & bksq)
- || (stm == WHITE && (StepAttacksBB[PAWN][psq] & bksq)))
- res = INVALID;
-
- // The position is an immediate win if it is white to move and the white
- // pawn can be promoted without getting captured.
- else if ( rank_of(psq) == RANK_7
- && stm == WHITE
- && wksq != psq + DELTA_N
- && ( square_distance(bksq, psq + DELTA_N) > 1
- ||(k_attacks<WHITE>() & (psq + DELTA_N))))
- res = WIN;
-
- // Check for known draw positions
- //
- // Case 1: Stalemate
- else if ( stm == BLACK
- && !(k_attacks<BLACK>() & ~(k_attacks<WHITE>() | StepAttacksBB[PAWN][psq])))
- res = DRAW;
-
- // Case 2: King can capture undefended pawn
- else if ( stm == BLACK
- && (k_attacks<BLACK>() & psq & ~k_attacks<WHITE>()))
- res = DRAW;
-
- // Case 3: Black king in front of white pawn
- else if ( bksq == psq + DELTA_N
- && rank_of(psq) < RANK_7)
- res = DRAW;
-
- // Case 4: White king in front of pawn and black has opposition
- else if ( stm == WHITE
- && wksq == psq + DELTA_N
- && bksq == wksq + DELTA_N + DELTA_N
- && rank_of(psq) < RANK_5)
- res = DRAW;
-
- // Case 5: Stalemate with rook pawn
- else if ( bksq == SQ_A8
- && file_of(psq) == FILE_A)
- res = DRAW;
-
- // Case 6: White king trapped on the rook file
- else if ( file_of(wksq) == FILE_A
- && file_of(psq) == FILE_A
- && rank_of(wksq) > rank_of(psq)
- && bksq == wksq + 2)
- res = DRAW;
-
- else
- res = UNKNOWN;
- }
-
- template<Color Us>
- Result KPKPosition::classify(const std::vector<KPKPosition>& db) {
-
- // White to Move: If one move leads to a position classified as RESULT_WIN,
- // the result of the current position is RESULT_WIN. If all moves lead to
- // positions classified as RESULT_DRAW, the current position is classified
- // RESULT_DRAW otherwise the current position is classified as RESULT_UNKNOWN.
- //
- // Black to Move: If one move leads to a position classified as RESULT_DRAW,
- // the result of the current position is RESULT_DRAW. If all moves lead to
- // positions classified as RESULT_WIN, the position is classified RESULT_WIN.
- // Otherwise, the current position is classified as RESULT_UNKNOWN.
-
- Result r = INVALID;
- Bitboard b = k_attacks<Us>();
-
- while (b)
- {
- r |= Us == WHITE ? db[index(BLACK, bksq, pop_lsb(&b), psq)]
- : db[index(WHITE, pop_lsb(&b), wksq, psq)];
-
- if (Us == WHITE && (r & WIN))
- return res = WIN;
-
- if (Us == BLACK && (r & DRAW))
- return res = DRAW;
- }
-
- if (Us == WHITE && rank_of(psq) < RANK_7)
- {
- Square s = psq + DELTA_N;
- r |= db[index(BLACK, bksq, wksq, s)]; // Single push
-
- if (rank_of(s) == RANK_3 && s != wksq && s != bksq)
- r |= db[index(BLACK, bksq, wksq, s + DELTA_N)]; // Double push
-
- if (r & WIN)
- return res = WIN;
- }
-
- return res = r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN;
- }
-
-}
projects / stockfish / blobdiff