/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2009 Marco Costalba
+ 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
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
-
-////
-//// Includes
-////
-
#include <cassert>
-#include "bitbase.h"
#include "bitboard.h"
-#include "move.h"
-#include "square.h"
-
-
-////
-//// Local definitions
-////
+#include "types.h"
namespace {
enum Result {
- RESULT_UNKNOWN,
- RESULT_INVALID,
- RESULT_WIN,
- RESULT_LOSS,
- RESULT_DRAW
- };
-
- struct KPKPosition {
- void from_index(int index);
- int to_index() const;
- bool is_legal() const;
- bool is_immediate_draw() const;
- bool is_immediate_win() const;
- Bitboard wk_attacks() const;
- Bitboard bk_attacks() const;
- Bitboard pawn_attacks() const;
-
- Square whiteKingSquare, blackKingSquare, pawnSquare;
- Color sideToMove;
+ INVALID = 0,
+ UNKNOWN = 1,
+ DRAW = 2,
+ WIN = 4
};
+ inline Result& operator|=(Result& r, Result v) { return r = Result(r | v); }
- Result *Bitbase;
- const int IndexMax = 2*24*64*64;
- int UnknownCount = 0;
+ struct KPKPosition {
- void initialize();
- bool next_iteration();
- Result classify_wtm(const KPKPosition &p);
- Result classify_btm(const KPKPosition &p);
- int compute_index(Square wksq, Square bksq, Square psq, Color stm);
- int compress_result(Result r);
+ Result classify_leaf(int idx);
+ Result classify(int idx, Result db[]);
-}
+ private:
+ template<Color Us> Result classify(const Result db[]) const;
+ template<Color Us> Bitboard k_attacks() const {
+ return Us == WHITE ? StepAttacksBB[W_KING][wksq] : StepAttacksBB[B_KING][bksq];
+ }
-////
-//// Functions
-////
+ Bitboard p_attacks() const { return StepAttacksBB[W_PAWN][psq]; }
+ void decode_index(int idx);
-void generate_kpk_bitbase(uint8_t bitbase[]) {
- // Allocate array and initialize:
- Bitbase = new Result[IndexMax];
- initialize();
+ Square wksq, bksq, psq;
+ Color stm;
+ };
- // Iterate until all positions are classified:
- while(next_iteration());
+ // The possible pawns squares are 24, the first 4 files and ranks from 2 to 7
+ const int IndexMax = 2 * 24 * 64 * 64; // stm * wp_sq * wk_sq * bk_sq = 196608
- // Compress bitbase into the supplied parameter:
- int i, j, b;
- for(i = 0; i < 24576; i++) {
- for(b = 0, j = 0; j < 8; b |= (compress_result(Bitbase[8*i+j]) << j), j++);
- assert(b == int(uint8_t(b)));
- bitbase[i] = (uint8_t)b;
- }
+ // Each uint32_t stores results of 32 positions, one per bit
+ uint32_t KPKBitbase[IndexMax / 32];
- // Release allocated memory:
- delete [] Bitbase;
+ int index(Square wksq, Square bksq, Square psq, Color stm);
}
-namespace {
-
- void KPKPosition::from_index(int index) {
- int s;
- sideToMove = Color(index % 2);
- blackKingSquare = Square((index / 2) % 64);
- whiteKingSquare = Square((index / 128) % 64);
- s = (index / 8192) % 24;
- pawnSquare = make_square(File(s % 4), Rank(s / 4 + 1));
- }
-
+uint32_t Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
- int KPKPosition::to_index() const {
- return compute_index(whiteKingSquare, blackKingSquare, pawnSquare,
- sideToMove);
- }
-
-
- bool KPKPosition::is_legal() const {
- if(whiteKingSquare == pawnSquare || whiteKingSquare == blackKingSquare ||
- pawnSquare == blackKingSquare)
- return false;
- if(sideToMove == WHITE) {
- if(bit_is_set(this->wk_attacks(), blackKingSquare))
- return false;
- if(bit_is_set(this->pawn_attacks(), blackKingSquare))
- return false;
- }
- else {
- if(bit_is_set(this->bk_attacks(), whiteKingSquare))
- return false;
- }
- return true;
- }
+ int idx = index(wksq, bksq, wpsq, stm);
+ return KPKBitbase[idx / 32] & (1 << (idx & 31));
+}
- bool KPKPosition::is_immediate_draw() const {
- if(sideToMove == BLACK) {
- Bitboard wka = this->wk_attacks();
- Bitboard bka = this->bk_attacks();
+void Bitbases::init_kpk() {
- // Case 1: Stalemate
- if((bka & ~(wka | this->pawn_attacks())) == EmptyBoardBB)
- return true;
+ Result db[IndexMax];
+ KPKPosition pos;
+ int idx, bit, repeat = 1;
- // Case 2: King can capture pawn
- if(bit_is_set(bka, pawnSquare) && !bit_is_set(wka, pawnSquare))
- return true;
- }
- else {
- // Case 1: Stalemate
- if(whiteKingSquare == SQ_A8 && pawnSquare == SQ_A7 &&
- (blackKingSquare == SQ_C7 || blackKingSquare == SQ_C8))
- return true;
- }
+ // Initialize table with known win / draw positions
+ for (idx = 0; idx < IndexMax; idx++)
+ db[idx] = pos.classify_leaf(idx);
- return false;
- }
+ // Iterate until all positions are classified (30 cycles needed)
+ while (repeat)
+ for (repeat = idx = 0; idx < IndexMax; idx++)
+ if (db[idx] == UNKNOWN && (db[idx] = pos.classify(idx, db)) != UNKNOWN)
+ repeat = 1;
-
- bool KPKPosition::is_immediate_win() const {
- // The position is an immediate win if it is white to move and the white
- // pawn can be promoted without getting captured:
- return
- sideToMove == WHITE &&
- square_rank(pawnSquare) == RANK_7 &&
- (square_distance(blackKingSquare, pawnSquare+DELTA_N) > 1 ||
- bit_is_set(this->wk_attacks(), pawnSquare+DELTA_N));
- }
+ // Map 32 position results into one KPKBitbase[] entry
+ for (idx = 0; idx < IndexMax / 32; idx++)
+ for (bit = 0; bit < 32; bit++)
+ if (db[32 * idx + bit] == WIN)
+ KPKBitbase[idx] |= 1 << bit;
+}
- Bitboard KPKPosition::wk_attacks() const {
- return StepAttackBB[WK][whiteKingSquare];
- }
+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)
- Bitboard KPKPosition::bk_attacks() const {
- return StepAttackBB[BK][blackKingSquare];
- }
+ int index(Square w, Square b, Square p, Color c) {
+ assert(file_of(p) <= FILE_D);
- Bitboard KPKPosition::pawn_attacks() const {
- return StepAttackBB[WP][pawnSquare];
+ return c + (b << 1) + (w << 7) + (file_of(p) << 13) + ((rank_of(p) - 1) << 15);
}
+ void KPKPosition::decode_index(int idx) {
- void initialize() {
- KPKPosition p;
- for(int i = 0; i < IndexMax; i++) {
- p.from_index(i);
- if(!p.is_legal())
- Bitbase[i] = RESULT_INVALID;
- else if(p.is_immediate_draw())
- Bitbase[i] = RESULT_DRAW;
- else if(p.is_immediate_win())
- Bitbase[i] = RESULT_WIN;
- else {
- Bitbase[i] = RESULT_UNKNOWN;
- UnknownCount++;
- }
- }
+ stm = Color(idx & 1);
+ bksq = Square((idx >> 1) & 63);
+ wksq = Square((idx >> 7) & 63);
+ psq = File((idx >> 13) & 3) | Rank((idx >> 15) + 1);
}
+ Result KPKPosition::classify_leaf(int idx) {
- bool next_iteration() {
- KPKPosition p;
- int previousUnknownCount = UnknownCount;
-
- for(int i = 0; i < IndexMax; i++)
- if(Bitbase[i] == RESULT_UNKNOWN) {
- p.from_index(i);
-
- Bitbase[i] = (p.sideToMove == WHITE)? classify_wtm(p) : classify_btm(p);
+ decode_index(idx);
- if(Bitbase[i] == RESULT_WIN || Bitbase[i] == RESULT_LOSS ||
- Bitbase[i] == RESULT_DRAW)
- UnknownCount--;
- }
+ // 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 && (p_attacks() & bksq)))
+ return INVALID;
- return UnknownCount != previousUnknownCount;
+ // 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(psq) == RANK_7
+ && stm == WHITE
+ && wksq != psq + DELTA_N
+ && ( square_distance(bksq, psq + DELTA_N) > 1
+ ||(k_attacks<WHITE>() & (psq + DELTA_N))))
+ return WIN;
+
+ // Check for known draw positions
+ //
+ // Case 1: Stalemate
+ if ( stm == BLACK
+ && !(k_attacks<BLACK>() & ~(k_attacks<WHITE>() | p_attacks())))
+ return DRAW;
+
+ // Case 2: King can capture undefended pawn
+ if ( stm == BLACK
+ && (k_attacks<BLACK>() & psq & ~k_attacks<WHITE>()))
+ return DRAW;
+
+ // Case 3: Black king in front of white pawn
+ if ( bksq == psq + DELTA_N
+ && rank_of(psq) < RANK_7)
+ return DRAW;
+
+ // Case 4: White king in front of pawn and black has opposition
+ if ( stm == WHITE
+ && wksq == psq + DELTA_N
+ && bksq == wksq + DELTA_N + DELTA_N
+ && rank_of(psq) < RANK_5)
+ return DRAW;
+
+ // Case 5: Stalemate with rook pawn
+ if ( bksq == SQ_A8
+ && file_of(psq) == FILE_A)
+ return DRAW;
+
+ // Case 6: White king trapped on the rook file
+ if ( file_of(wksq) == FILE_A
+ && file_of(psq) == FILE_A
+ && rank_of(wksq) > rank_of(psq)
+ && bksq == wksq + 2)
+ return DRAW;
+
+ return UNKNOWN;
}
+ template<Color Us>
+ Result KPKPosition::classify(const Result db[]) const {
- Result classify_wtm(const KPKPosition &p) {
-
- // If one move leads to a position classified as RESULT_LOSS, the result
- // of the current position is RESULT_WIN. If all moves lead to positions
- // classified as RESULT_DRAW, the current position is classified as
- // RESULT_DRAW. Otherwise, the current position is classified as
- // RESULT_UNKNOWN.
-
- bool unknownFound = false;
- Bitboard b;
- Square s;
+ // 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.
- // King moves
- b = p.wk_attacks();
- while(b) {
- s = pop_1st_bit(&b);
- switch(Bitbase[compute_index(s, p.blackKingSquare, p.pawnSquare,
- BLACK)]) {
- case RESULT_LOSS:
- return RESULT_WIN;
+ Result r = INVALID;
+ Bitboard b = k_attacks<Us>();
- case RESULT_UNKNOWN:
- unknownFound = true;
- break;
+ while (b)
+ {
+ r |= Us == WHITE ? db[index(pop_lsb(&b), bksq, psq, BLACK)]
+ : db[index(wksq, pop_lsb(&b), psq, WHITE)];
- case RESULT_DRAW: case RESULT_INVALID:
- break;
+ if (Us == WHITE && (r & WIN))
+ return WIN;
- default:
- assert(false);
- }
+ if (Us == BLACK && (r & DRAW))
+ return DRAW;
}
- // Pawn moves
- if(square_rank(p.pawnSquare) < RANK_7) {
- s = p.pawnSquare + DELTA_N;
- switch(Bitbase[compute_index(p.whiteKingSquare, p.blackKingSquare, s,
- BLACK)]) {
- case RESULT_LOSS:
- return RESULT_WIN;
-
- case RESULT_UNKNOWN:
- unknownFound = true;
- break;
-
- case RESULT_DRAW: case RESULT_INVALID:
- break;
-
- default:
- assert(false);
- }
-
- if(square_rank(s) == RANK_3 &&
- s != p.whiteKingSquare && s != p.blackKingSquare) {
- s += DELTA_N;
- switch(Bitbase[compute_index(p.whiteKingSquare, p.blackKingSquare, s,
- BLACK)]) {
- case RESULT_LOSS:
- return RESULT_WIN;
-
- case RESULT_UNKNOWN:
- unknownFound = true;
- break;
-
- case RESULT_DRAW: case RESULT_INVALID:
- break;
-
- default:
- assert(false);
- }
- }
- }
-
- return unknownFound? RESULT_UNKNOWN : RESULT_DRAW;
- }
-
-
- Result classify_btm(const KPKPosition &p) {
-
- // 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 current position is classified as
- // RESULT_LOSS. Otherwise, the current position is classified as
- // RESULT_UNKNOWN.
+ if (Us == WHITE && rank_of(psq) < RANK_7)
+ {
+ Square s = psq + DELTA_N;
+ r |= db[index(wksq, bksq, s, BLACK)]; // Single push
- bool unknownFound = false;
- Bitboard b;
- Square s;
+ if (rank_of(s) == RANK_3 && s != wksq && s != bksq)
+ r |= db[index(wksq, bksq, s + DELTA_N, BLACK)]; // Double push
- // King moves
- b = p.bk_attacks();
- while(b) {
- s = pop_1st_bit(&b);
- switch(Bitbase[compute_index(p.whiteKingSquare, s, p.pawnSquare,
- WHITE)]) {
- case RESULT_DRAW:
- return RESULT_DRAW;
-
- case RESULT_UNKNOWN:
- unknownFound = true;
- break;
-
- case RESULT_WIN: case RESULT_INVALID:
- break;
-
- default:
- assert(false);
- }
+ if (r & WIN)
+ return WIN;
}
- return unknownFound? RESULT_UNKNOWN : RESULT_LOSS;
- }
-
-
- int compute_index(Square wksq, Square bksq, Square psq, Color stm) {
- int p = int(square_file(psq)) + (int(square_rank(psq)) - 1) * 4;
- int result = int(stm) + 2*int(bksq) + 128*int(wksq) + 8192*p;
- assert(result >= 0 && result < IndexMax);
- return result;
+ return r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN;
}
+ Result KPKPosition::classify(int idx, Result db[]) {
- int compress_result(Result r) {
- return (r == RESULT_WIN || r == RESULT_LOSS)? 1 : 0;
+ decode_index(idx);
+ return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db);
}
}
projects / stockfish / blobdiff