RESULT_UNKNOWN,
RESULT_INVALID,
RESULT_WIN,
- RESULT_LOSS,
RESULT_DRAW
};
struct KPKPosition {
+ Result classify_knowns(int index);
+ Result classify(int index, Result db[]);
+
+ private:
void from_index(int index);
- bool is_legal() const;
- bool is_immediate_draw() const;
- bool is_immediate_win() const;
+ 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]; }
};
// 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
+ 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];
- 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 wpsq, Color stm);
}
}
-void init_kpk_bitbase() {
+void kpk_bitbase_init() {
- Result bb[IndexMax];
+ Result db[IndexMax];
KPKPosition pos;
- bool repeat;
+ int index, bit, repeat = 1;
// Initialize table
- for (int 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;
- }
+ for (index = 0; index < IndexMax; index++)
+ db[index] = pos.classify_knowns(index);
// Iterate until all positions are classified (30 cycles needed)
- do {
- repeat = false;
-
- for (int 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);
+ 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 (int i = 0; i < IndexMax / 32; i++)
- for (int j = 0; j < 32; j++)
- if (bb[32 * i + j] == RESULT_WIN || bb[32 * i + j] == RESULT_LOSS)
- KPKBitbase[i] |= (1 << j);
+ 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)
+ // 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(square_file(wpsq) <= FILE_D);
- int p = int(square_file(wpsq)) + 4 * int(square_rank(wpsq) - 1);
- int r = int(stm) + 2 * int(bksq) + 128 * int(wksq) + 8192 * p;
+ int p = square_file(wpsq) + 4 * (square_rank(wpsq) - 1);
+ int r = stm + 2 * bksq + 128 * wksq + 8192 * p;
assert(r >= 0 && r < IndexMax);
void KPKPosition::from_index(int index) {
- int s = (index / 8192) % 24;
-
- sideToMove = Color(index % 2);
- blackKingSquare = Square((index / 2) % 64);
- whiteKingSquare = Square((index / 128) % 64);
- pawnSquare = make_square(File(s % 4), Rank(s / 4 + 1));
+ 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));
}
- bool KPKPosition::is_legal() const {
+ 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 false;
-
- 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;
-
- return true;
- }
+ return RESULT_INVALID;
- bool KPKPosition::is_immediate_draw() const {
+ // 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;
- if (sideToMove == BLACK)
- {
- Bitboard wka = wk_attacks();
- Bitboard bka = bk_attacks();
-
- // Case 1: Stalemate
- if ((bka & ~(wka | pawn_attacks())) == EmptyBoardBB)
- return true;
-
- // Case 2: King can capture pawn
- if (bit_is_set(bka, pawnSquare) && !bit_is_set(wka, pawnSquare))
- return true;
- }
- else
- {
- // Case 1: Stalemate (possible pawn files are only from A to D)
- if ( whiteKingSquare == SQ_A8
- && pawnSquare == SQ_A7
- && (blackKingSquare == SQ_C7 || blackKingSquare == SQ_C8))
- return true;
- }
- return false;
+ // The position is an immediate win if it is white to move and the
+ // white pawn can be promoted without getting captured.
+ if ( square_rank(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
+ && square_rank(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
+ && square_rank(pawnSquare) < RANK_5
+ && sideToMove == WHITE)
+ return RESULT_DRAW;
+
+ // Case 5: Stalemate with rook pawn
+ if ( blackKingSquare == SQ_A8
+ && square_file(pawnSquare) == FILE_A)
+ return RESULT_DRAW;
+
+ return RESULT_UNKNOWN;
}
- bool KPKPosition::is_immediate_win() const {
+ Result KPKPosition::classify(int index, Result 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));
+ from_index(index);
+ db[index] = (sideToMove == WHITE ? classify_white(db) : classify_black(db));
+ return db[index];
}
- Result classify_wtm(const KPKPosition& pos, const Result bb[]) {
+ Result KPKPosition::classify_white(const Result db[]) {
- // If one move leads to a position classified as RESULT_LOSS, the result
+ // 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.
Result r;
// King moves
- b = pos.wk_attacks();
+ b = wk_attacks();
while (b)
{
s = pop_1st_bit(&b);
- r = bb[compute_index(s, pos.blackKingSquare, pos.pawnSquare, BLACK)];
+ r = db[compute_index(s, blackKingSquare, pawnSquare, BLACK)];
- if (r == RESULT_LOSS)
+ if (r == RESULT_WIN)
return RESULT_WIN;
if (r == RESULT_UNKNOWN)
}
// Pawn moves
- if (square_rank(pos.pawnSquare) < RANK_7)
+ if (square_rank(pawnSquare) < RANK_7)
{
- s = pos.pawnSquare + DELTA_N;
- r = bb[compute_index(pos.whiteKingSquare, pos.blackKingSquare, s, BLACK)];
+ s = pawnSquare + DELTA_N;
+ r = db[compute_index(whiteKingSquare, blackKingSquare, s, BLACK)];
- if (r == RESULT_LOSS)
+ if (r == RESULT_WIN)
return RESULT_WIN;
if (r == RESULT_UNKNOWN)
unknownFound = true;
// Double pawn push
- if ( square_rank(s) == RANK_3
- && s != pos.whiteKingSquare
- && s != pos.blackKingSquare)
+ if (square_rank(s) == RANK_3 && r != RESULT_INVALID)
{
s += DELTA_N;
- r = bb[compute_index(pos.whiteKingSquare, pos.blackKingSquare, s, BLACK)];
+ r = db[compute_index(whiteKingSquare, blackKingSquare, s, BLACK)];
- if (r == RESULT_LOSS)
+ if (r == RESULT_WIN)
return RESULT_WIN;
if (r == RESULT_UNKNOWN)
return unknownFound ? RESULT_UNKNOWN : RESULT_DRAW;
}
-
- Result classify_btm(const KPKPosition& pos, const Result bb[]) {
+ 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 current position is classified as
- // RESULT_LOSS. Otherwise, the current position is classified as
- // RESULT_UNKNOWN.
+ // 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;
Result r;
// King moves
- b = pos.bk_attacks();
+ b = bk_attacks();
while (b)
{
s = pop_1st_bit(&b);
- r = bb[compute_index(pos.whiteKingSquare, s, pos.pawnSquare, WHITE)];
+ 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_LOSS;
+ return unknownFound ? RESULT_UNKNOWN : RESULT_WIN;
}
}
projects / stockfish / blobdiff