/*
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
namespace {
enum Result {
- RESULT_UNKNOWN,
- RESULT_INVALID,
- RESULT_WIN,
- RESULT_DRAW
+ INVALID = 0,
+ UNKNOWN = 1,
+ DRAW = 2,
+ WIN = 4
};
+ inline Result& operator|=(Result& r, Result v) { return r = Result(r | v); }
+
struct KPKPosition {
- Result classify_knowns(int index);
- Result classify(int index, Result db[]);
+
+ Result classify_leaf(int idx);
+ Result classify(int idx, 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;
+ 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];
+ }
+
+ Bitboard p_attacks() const { return StepAttacksBB[W_PAWN][psq]; }
+ void decode_index(int idx);
+
+ Square wksq, bksq, psq;
+ Color stm;
};
// 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
+ const int IndexMax = 2 * 24 * 64 * 64; // stm * 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);
+ int index(Square wksq, Square bksq, Square psq, Color stm);
}
-uint32_t probe_kpk_bitbase(Square wksq, Square wpsq, Square bksq, Color stm) {
+uint32_t Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
- int index = compute_index(wksq, bksq, wpsq, stm);
-
- return KPKBitbase[index / 32] & (1 << (index & 31));
+ int idx = index(wksq, bksq, wpsq, stm);
+ return KPKBitbase[idx / 32] & (1 << (idx & 31));
}
-void kpk_bitbase_init() {
+void Bitbases::init_kpk() {
- Result db[IndexMax];
+ Result* db = new Result[IndexMax]; // Avoid to hit stack limit on some platforms
KPKPosition pos;
- int index, bit, repeat = 1;
+ int idx, bit, repeat = 1;
- // Initialize table
- for (index = 0; index < IndexMax; index++)
- db[index] = pos.classify_knowns(index);
+ // Initialize table with known win / draw positions
+ for (idx = 0; idx < IndexMax; idx++)
+ db[idx] = pos.classify_leaf(idx);
// 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)
+ for (repeat = idx = 0; idx < IndexMax; idx++)
+ if (db[idx] == UNKNOWN && (db[idx] = pos.classify(idx, db)) != UNKNOWN)
repeat = 1;
// Map 32 position results into one KPKBitbase[] entry
- for (index = 0; index < IndexMax / 32; index++)
+ for (idx = 0; idx < IndexMax / 32; idx++)
for (bit = 0; bit < 32; bit++)
- if (db[32 * index + bit] == RESULT_WIN)
- KPKBitbase[index] |= (1 << bit);
+ if (db[32 * idx + bit] == WIN)
+ KPKBitbase[idx] |= 1 << bit;
+
+ delete [] db;
}
// 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) {
+ int index(Square w, Square b, Square p, Color c) {
- assert(file_of(wpsq) <= FILE_D);
+ assert(file_of(p) <= 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;
+ return c + (b << 1) + (w << 7) + (file_of(p) << 13) + ((rank_of(p) - 1) << 15);
}
- void KPKPosition::from_index(int index) {
+ void KPKPosition::decode_index(int idx) {
- 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));
+ 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_knowns(int index) {
+ Result KPKPosition::classify_leaf(int idx) {
- from_index(index);
+ decode_index(idx);
- // Check if two pieces are on the same square
- if ( whiteKingSquare == pawnSquare
- || whiteKingSquare == blackKingSquare
- || blackKingSquare == pawnSquare)
- return RESULT_INVALID;
+ // 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;
- // 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;
+ // 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 ( sideToMove == BLACK
- && (bk_attacks() & ~(wk_attacks() | pawn_attacks())) == EmptyBoardBB)
- return RESULT_DRAW;
+ if ( stm == BLACK
+ && !(k_attacks<BLACK>() & ~(k_attacks<WHITE>() | p_attacks())))
+ return 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 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 ( blackKingSquare == pawnSquare + DELTA_N
- && rank_of(pawnSquare) < RANK_7)
- return RESULT_DRAW;
+ 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 ( whiteKingSquare == pawnSquare + DELTA_N
- && blackKingSquare == pawnSquare + DELTA_N + DELTA_N + DELTA_N
- && rank_of(pawnSquare) < RANK_5
- && sideToMove == WHITE)
- return RESULT_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 ( 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];
+ 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;
}
- Result KPKPosition::classify_white(const Result db[]) {
+ template<Color Us>
+ Result KPKPosition::classify(const Result db[]) const {
- // 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.
+ // 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.
- bool unknownFound = false;
- Bitboard b;
- Square s;
- Result r;
+ Result r = INVALID;
+ Bitboard b = k_attacks<Us>();
- // King moves
- b = wk_attacks();
while (b)
{
- s = pop_1st_bit(&b);
- r = db[compute_index(s, blackKingSquare, pawnSquare, BLACK)];
+ r |= Us == WHITE ? db[index(pop_lsb(&b), bksq, psq, BLACK)]
+ : db[index(wksq, pop_lsb(&b), psq, WHITE)];
- if (r == RESULT_WIN)
- return RESULT_WIN;
+ if (Us == WHITE && (r & WIN))
+ return WIN;
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
+ if (Us == BLACK && (r & DRAW))
+ return DRAW;
}
- // Pawn moves
- if (rank_of(pawnSquare) < RANK_7)
+ if (Us == WHITE && rank_of(psq) < 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;
+ Square s = psq + DELTA_N;
+ r |= db[index(wksq, bksq, s, BLACK)]; // Single push
- // Double pawn push
- if (rank_of(s) == RANK_3 && r != RESULT_INVALID)
- {
- s += DELTA_N;
- r = db[compute_index(whiteKingSquare, blackKingSquare, s, BLACK)];
+ if (rank_of(s) == RANK_3 && s != wksq && s != bksq)
+ r |= db[index(wksq, bksq, s + DELTA_N, BLACK)]; // Double push
- if (r == RESULT_WIN)
- return RESULT_WIN;
-
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
- }
+ if (r & WIN)
+ return WIN;
}
- 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)];
+ return r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN;
+ }
- if (r == RESULT_DRAW)
- return RESULT_DRAW;
+ Result KPKPosition::classify(int idx, Result db[]) {
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
- }
- return unknownFound ? RESULT_UNKNOWN : RESULT_WIN;
+ decode_index(idx);
+ return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db);
}
}
projects / stockfish / blobdiff