/*
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
+ 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
*/
#include <cassert>
+#include <vector>
#include "bitboard.h"
#include "types.h"
namespace {
- enum Result {
- RESULT_UNKNOWN,
- RESULT_INVALID,
- RESULT_WIN,
- RESULT_LOSS,
- RESULT_DRAW
- };
+ // 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);
+ }
- struct KPKPosition {
- void from_index(int index);
- bool is_legal() const;
- bool is_immediate_draw() const;
- bool is_immediate_win() const;
- 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;
+ enum Result {
+ INVALID = 0,
+ UNKNOWN = 1,
+ DRAW = 2,
+ WIN = 4
};
- const int IndexMax = 2 * 24 * 64 * 64;
-
- Result classify_wtm(const KPKPosition& pos, const Result bb[]);
- Result classify_btm(const KPKPosition& pos, const Result bb[]);
- int compute_index(Square wksq, Square bksq, Square psq, Color stm);
-}
-
+ inline Result& operator|=(Result& r, Result v) { return r = Result(r | v); }
-void generate_kpk_bitbase(uint8_t bitbase[]) {
+ struct KPKPosition {
- bool repeat;
- int i, j, b;
- KPKPosition pos;
- Result bb[IndexMax];
+ void classify_leaf(unsigned idx);
- // Initialize table
- for (i = 0; i < IndexMax; i++)
- {
- pos.from_index(i);
- bb[i] = !pos.is_legal() ? RESULT_INVALID
- : pos.is_immediate_draw() ? RESULT_DRAW
- : pos.is_immediate_win() ? RESULT_WIN : RESULT_UNKNOWN;
- }
+ Result classify(const std::vector<KPKPosition>& db)
+ { return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
- // Iterate until all positions are classified (30 cycles needed)
- do {
- repeat = false;
-
- for (i = 0; i < IndexMax; i++)
- if (bb[i] == RESULT_UNKNOWN)
- {
- pos.from_index(i);
-
- bb[i] = (pos.sideToMove == WHITE) ? classify_wtm(pos, bb)
- : classify_btm(pos, bb);
- if (bb[i] != RESULT_UNKNOWN)
- repeat = true;
- }
-
- } while (repeat);
-
- // Compress result and map into supplied bitbase parameter
- for (i = 0; i < 24576; i++)
- {
- b = 0;
- for (j = 0; j < 8; j++)
- if (bb[8*i+j] == RESULT_WIN || bb[8*i+j] == RESULT_LOSS)
- b |= (1 << j);
-
- bitbase[i] = (uint8_t)b;
- }
-}
+ operator Result() const { return res; }
+ private:
+ template<Color Us> Bitboard k_attacks() const
+ { return StepAttacksBB[KING][Us == WHITE ? wksq : bksq]; }
-namespace {
+ template<Color Us> Result classify(const std::vector<KPKPosition>& db);
- int compute_index(Square wksq, Square bksq, Square psq, Color stm) {
+ Color stm;
+ Square bksq, wksq, psq;
+ Result res;
+ };
- int p = int(square_file(psq)) + (int(square_rank(psq)) - 1) * 4;
- int r = int(stm) + 2 * int(bksq) + 128 * int(wksq) + 8192 * p;
+} // namespace
- assert(r >= 0 && r < IndexMax);
- return r;
- }
+bool Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
- void KPKPosition::from_index(int index) {
+ assert(file_of(wpsq) <= FILE_D);
- int s = (index / 8192) % 24;
+ unsigned idx = index(stm, bksq, wksq, wpsq);
+ return KPKBitbase[idx / 32] & (1 << (idx & 31));
+}
- sideToMove = Color(index % 2);
- blackKingSquare = Square((index / 2) % 64);
- whiteKingSquare = Square((index / 128) % 64);
- pawnSquare = make_square(File(s % 4), Rank(s / 4 + 1));
- }
- bool KPKPosition::is_legal() const {
+void Bitbases::init_kpk() {
- if ( whiteKingSquare == pawnSquare
- || whiteKingSquare == blackKingSquare
- || pawnSquare == blackKingSquare)
- return false;
+ unsigned idx, repeat = 1;
+ std::vector<KPKPosition> db(IndexMax);
- if (sideToMove == WHITE)
- {
- if ( bit_is_set(wk_attacks(), blackKingSquare)
- || bit_is_set(pawn_attacks(), blackKingSquare))
- return false;
- }
- else if (bit_is_set(bk_attacks(), whiteKingSquare))
- return false;
+ // Initialize db with known win / draw positions
+ for (idx = 0; idx < IndexMax; idx++)
+ db[idx].classify_leaf(idx);
- return true;
- }
+ // 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);
+}
- bool KPKPosition::is_immediate_draw() const {
- if (sideToMove == BLACK)
- {
- Bitboard wka = wk_attacks();
- Bitboard bka = bk_attacks();
+namespace {
- // Case 1: Stalemate
- if ((bka & ~(wka | pawn_attacks())) == EmptyBoardBB)
- return true;
+ 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;
- // 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;
-
- if ( whiteKingSquare == SQ_H8
- && pawnSquare == SQ_H7
- && (blackKingSquare == SQ_F7 || blackKingSquare == SQ_F8))
- return true;
- }
- return false;
+ res = UNKNOWN;
}
- bool KPKPosition::is_immediate_win() const {
+ template<Color Us>
+ Result KPKPosition::classify(const std::vector<KPKPosition>& db) {
- // 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
- && whiteKingSquare != pawnSquare + DELTA_N
- && ( square_distance(blackKingSquare, pawnSquare + DELTA_N) > 1
- || bit_is_set(wk_attacks(), pawnSquare + DELTA_N));
- }
-
- Result classify_wtm(const KPKPosition& pos, const Result bb[]) {
+ // 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.
- // 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 RESULT_DRAW
- // otherwise the current position is classified as RESULT_UNKNOWN.
+ Result r = INVALID;
+ Bitboard b = k_attacks<Us>();
- bool unknownFound = false;
- Bitboard b;
- Square s;
- int idx;
-
- // King moves
- b = pos.wk_attacks();
while (b)
{
- s = pop_1st_bit(&b);
- idx = compute_index(s, pos.blackKingSquare, pos.pawnSquare, BLACK);
-
- switch (bb[idx]) {
+ r |= Us == WHITE ? db[index(BLACK, bksq, pop_lsb(&b), psq)]
+ : db[index(WHITE, pop_lsb(&b), wksq, psq)];
- case RESULT_LOSS:
- return RESULT_WIN;
+ if (Us == WHITE && (r & WIN))
+ return res = WIN;
- case RESULT_UNKNOWN:
- unknownFound = true;
-
- case RESULT_DRAW:
- case RESULT_INVALID:
- break;
-
- default:
- assert(false);
- }
+ if (Us == BLACK && (r & DRAW))
+ return res = DRAW;
}
- // Pawn moves
- if (square_rank(pos.pawnSquare) < RANK_7)
+ if (Us == WHITE && rank_of(psq) < RANK_7)
{
- s = pos.pawnSquare + DELTA_N;
- idx = compute_index(pos.whiteKingSquare, pos.blackKingSquare, s, BLACK);
-
- switch (bb[idx]) {
-
- case RESULT_LOSS:
- return RESULT_WIN;
-
- case RESULT_UNKNOWN:
- unknownFound = true;
-
- case RESULT_DRAW:
- case RESULT_INVALID:
- break;
-
- default:
- assert(false);
- }
-
- // Double pawn push
- if ( square_rank(s) == RANK_3
- && s != pos.whiteKingSquare
- && s != pos.blackKingSquare)
- {
- s += DELTA_N;
- idx = compute_index(pos.whiteKingSquare, pos.blackKingSquare, s, BLACK);
-
- switch (bb[idx]) {
-
- case RESULT_LOSS:
- return RESULT_WIN;
+ Square s = psq + DELTA_N;
+ r |= db[index(BLACK, bksq, wksq, s)]; // Single push
- case RESULT_UNKNOWN:
- unknownFound = true;
+ if (rank_of(s) == RANK_3 && s != wksq && s != bksq)
+ r |= db[index(BLACK, bksq, wksq, s + DELTA_N)]; // Double push
- case RESULT_DRAW:
- case RESULT_INVALID:
- break;
-
- default:
- assert(false);
- }
- }
+ if (r & WIN)
+ return res = WIN;
}
- return unknownFound ? RESULT_UNKNOWN : RESULT_DRAW;
- }
-
-
- Result classify_btm(const KPKPosition& pos, const Result bb[]) {
-
- // 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.
-
- bool unknownFound = false;
- Bitboard b;
- Square s;
- int idx;
-
- // King moves
- b = pos.bk_attacks();
- while (b)
- {
- s = pop_1st_bit(&b);
- idx = compute_index(pos.whiteKingSquare, s, pos.pawnSquare, WHITE);
-
- switch (bb[idx]) {
-
- case RESULT_DRAW:
- return RESULT_DRAW;
- case RESULT_UNKNOWN:
- unknownFound = true;
-
- case RESULT_WIN:
- case RESULT_INVALID:
- break;
-
- default:
- assert(false);
- }
- }
- return unknownFound ? RESULT_UNKNOWN : RESULT_LOSS;
+ return res = r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN;
}
}
projects / stockfish / blobdiff