+++ /dev/null
-/*
- Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2010 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 "bitboard.h"
-#include "types.h"
-
-namespace {
-
- enum Result {
- RESULT_UNKNOWN,
- RESULT_INVALID,
- RESULT_WIN,
- RESULT_DRAW
- };
-
- struct KPKPosition {
- Result classify_knowns(int index);
- Result classify(int index, Result db[]);
-
- private:
- void from_index(int index);
- Result classify_white(const Result db[]);
- Result classify_black(const Result db[]);
- Bitboard wk_attacks() const { return StepAttacksBB[WK][whiteKingSquare]; }
- Bitboard bk_attacks() const { return StepAttacksBB[BK][blackKingSquare]; }
- Bitboard pawn_attacks() const { return StepAttacksBB[WP][pawnSquare]; }
-
- Square whiteKingSquare, blackKingSquare, pawnSquare;
- Color sideToMove;
- };
-
- // The possible pawns squares are 24, the first 4 files and ranks from 2 to 7
- const int IndexMax = 2 * 24 * 64 * 64; // color * wp_sq * wk_sq * bk_sq = 196608
-
- // Each uint32_t stores results of 32 positions, one per bit
- uint32_t KPKBitbase[IndexMax / 32];
-
- int compute_index(Square wksq, Square bksq, Square wpsq, Color stm);
-}
-
-
-uint32_t probe_kpk_bitbase(Square wksq, Square wpsq, Square bksq, Color stm) {
-
- int index = compute_index(wksq, bksq, wpsq, stm);
-
- return KPKBitbase[index / 32] & (1 << (index & 31));
-}
-
-
-void kpk_bitbase_init() {
-
- Result db[IndexMax];
- KPKPosition pos;
- int index, bit, repeat = 1;
-
- // Initialize table
- for (index = 0; index < IndexMax; index++)
- db[index] = pos.classify_knowns(index);
-
- // Iterate until all positions are classified (30 cycles needed)
- while (repeat)
- for (repeat = index = 0; index < IndexMax; index++)
- if ( db[index] == RESULT_UNKNOWN
- && pos.classify(index, db) != RESULT_UNKNOWN)
- repeat = 1;
-
- // Map 32 position results into one KPKBitbase[] entry
- for (index = 0; index < IndexMax / 32; index++)
- for (bit = 0; bit < 32; bit++)
- if (db[32 * index + bit] == RESULT_WIN)
- KPKBitbase[index] |= (1 << bit);
-}
-
-
-namespace {
-
- // 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)
-
- int compute_index(Square wksq, Square bksq, Square wpsq, Color stm) {
-
- assert(file_of(wpsq) <= FILE_D);
-
- int p = file_of(wpsq) + 4 * (rank_of(wpsq) - 1);
- int r = stm + 2 * bksq + 128 * wksq + 8192 * p;
-
- assert(r >= 0 && r < IndexMax);
-
- return r;
- }
-
- void KPKPosition::from_index(int index) {
-
- int s = index >> 13;
- sideToMove = Color(index & 1);
- blackKingSquare = Square((index >> 1) & 63);
- whiteKingSquare = Square((index >> 7) & 63);
- pawnSquare = make_square(File(s & 3), Rank((s >> 2) + 1));
- }
-
- Result KPKPosition::classify_knowns(int index) {
-
- from_index(index);
-
- // Check if two pieces are on the same square
- if ( whiteKingSquare == pawnSquare
- || whiteKingSquare == blackKingSquare
- || blackKingSquare == pawnSquare)
- return RESULT_INVALID;
-
- // Check if a king can be captured
- if ( bit_is_set(wk_attacks(), blackKingSquare)
- || (bit_is_set(pawn_attacks(), blackKingSquare) && sideToMove == WHITE))
- return RESULT_INVALID;
-
- // The position is an immediate win if it is white to move and the
- // white pawn can be promoted without getting captured.
- if ( rank_of(pawnSquare) == RANK_7
- && sideToMove == WHITE
- && whiteKingSquare != pawnSquare + DELTA_N
- && ( square_distance(blackKingSquare, pawnSquare + DELTA_N) > 1
- || bit_is_set(wk_attacks(), pawnSquare + DELTA_N)))
- return RESULT_WIN;
-
- // Check for known draw positions
- //
- // Case 1: Stalemate
- if ( sideToMove == BLACK
- && (bk_attacks() & ~(wk_attacks() | pawn_attacks())) == EmptyBoardBB)
- return RESULT_DRAW;
-
- // Case 2: King can capture pawn
- if ( sideToMove == BLACK
- && bit_is_set(bk_attacks(), pawnSquare) && !bit_is_set(wk_attacks(), pawnSquare))
- return RESULT_DRAW;
-
- // Case 3: Black king in front of white pawn
- if ( blackKingSquare == pawnSquare + DELTA_N
- && rank_of(pawnSquare) < RANK_7)
- return RESULT_DRAW;
-
- // Case 4: White king in front of pawn and black has opposition
- if ( whiteKingSquare == pawnSquare + DELTA_N
- && blackKingSquare == pawnSquare + DELTA_N + DELTA_N + DELTA_N
- && rank_of(pawnSquare) < RANK_5
- && sideToMove == WHITE)
- return RESULT_DRAW;
-
- // Case 5: Stalemate with rook pawn
- if ( blackKingSquare == SQ_A8
- && file_of(pawnSquare) == FILE_A)
- return RESULT_DRAW;
-
- return RESULT_UNKNOWN;
- }
-
- Result KPKPosition::classify(int index, Result db[]) {
-
- from_index(index);
- db[index] = (sideToMove == WHITE ? classify_white(db) : classify_black(db));
- return db[index];
- }
-
- Result KPKPosition::classify_white(const Result db[]) {
-
- // 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.
-
- bool unknownFound = false;
- Bitboard b;
- Square s;
- Result r;
-
- // King moves
- b = wk_attacks();
- while (b)
- {
- s = pop_1st_bit(&b);
- r = db[compute_index(s, blackKingSquare, pawnSquare, BLACK)];
-
- if (r == RESULT_WIN)
- return RESULT_WIN;
-
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
- }
-
- // Pawn moves
- if (rank_of(pawnSquare) < RANK_7)
- {
- s = pawnSquare + DELTA_N;
- r = db[compute_index(whiteKingSquare, blackKingSquare, s, BLACK)];
-
- if (r == RESULT_WIN)
- return RESULT_WIN;
-
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
-
- // Double pawn push
- if (rank_of(s) == RANK_3 && r != RESULT_INVALID)
- {
- s += DELTA_N;
- r = db[compute_index(whiteKingSquare, blackKingSquare, s, BLACK)];
-
- if (r == RESULT_WIN)
- return RESULT_WIN;
-
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
- }
- }
- return unknownFound ? RESULT_UNKNOWN : RESULT_DRAW;
- }
-
- Result KPKPosition::classify_black(const Result db[]) {
-
- // 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 as RESULT_WIN.
- // Otherwise, the current position is classified as RESULT_UNKNOWN.
-
- bool unknownFound = false;
- Bitboard b;
- Square s;
- Result r;
-
- // King moves
- b = bk_attacks();
- while (b)
- {
- s = pop_1st_bit(&b);
- r = db[compute_index(whiteKingSquare, s, pawnSquare, WHITE)];
-
- if (r == RESULT_DRAW)
- return RESULT_DRAW;
-
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
- }
- return unknownFound ? RESULT_UNKNOWN : RESULT_WIN;
- }
-
-}
projects / stockfish / blobdiff