*/
#include <cassert>
+#include <vector>
#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[W_KING][whiteKingSquare]; }
- Bitboard bk_attacks() const { return StepAttacksBB[B_KING][blackKingSquare]; }
- Bitboard pawn_attacks() const { return StepAttacksBB[W_PAWN][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
+ 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];
- int compute_index(Square wksq, Square bksq, Square wpsq, Color stm);
-}
+ // 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 6 - rank (from 6 - RANK_7 to 6 - RANK_2)
+ unsigned index(Color stm, Square bksq, Square wksq, Square psq) {
+ return stm + (bksq << 1) + (wksq << 7) + (file_of(psq) << 13) + ((6 - rank_of(psq)) << 15);
+ }
+ enum Result {
+ INVALID = 0,
+ UNKNOWN = 1,
+ DRAW = 2,
+ WIN = 4
+ };
-uint32_t probe_kpk_bitbase(Square wksq, Square wpsq, Square bksq, Color stm) {
+ inline Result& operator|=(Result& r, Result v) { return r = Result(r | v); }
- int index = compute_index(wksq, bksq, wpsq, stm);
+ struct KPKPosition {
- return KPKBitbase[index / 32] & (1 << (index & 31));
-}
+ void classify_leaf(unsigned idx);
+ Result classify(const std::vector<KPKPosition>& db)
+ { return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
-void kpk_bitbase_init() {
+ operator Result() const { return res; }
- Result db[IndexMax];
- KPKPosition pos;
- int index, bit, repeat = 1;
+ private:
+ template<Color Us> Bitboard k_attacks() const
+ { return StepAttacksBB[KING][Us == WHITE ? wksq : bksq]; }
- // Initialize table
- for (index = 0; index < IndexMax; index++)
- db[index] = pos.classify_knowns(index);
+ template<Color Us> Result classify(const std::vector<KPKPosition>& db);
- // 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;
+ Color stm;
+ Square bksq, wksq, psq;
+ Result res;
+ };
- // 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
-namespace {
+bool Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
- // 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)
+ assert(file_of(wpsq) <= FILE_D);
- int compute_index(Square wksq, Square bksq, Square wpsq, Color stm) {
+ unsigned idx = index(stm, bksq, wksq, wpsq);
+ return KPKBitbase[idx / 32] & (1 << (idx & 31));
+}
- 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;
+void Bitbases::init_kpk() {
- assert(r >= 0 && r < IndexMax);
+ unsigned idx, repeat = 1;
+ std::vector<KPKPosition> db(IndexMax);
- return r;
- }
+ // Initialize db with known win / draw positions
+ for (idx = 0; idx < IndexMax; idx++)
+ db[idx].classify_leaf(idx);
+
+ // Iterate until all positions are classified (26 cycles needed)
+ while (repeat)
+ for (repeat = idx = 0; idx < IndexMax; idx++)
+ if (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN)
+ repeat = 1;
- void KPKPosition::from_index(int index) {
+ // Map 32 results into one KPKBitbase[] entry
+ for (idx = 0; idx < IndexMax; idx++)
+ if (db[idx] == WIN)
+ KPKBitbase[idx / 32] |= 1 << (idx & 31);
+}
- 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) {
+namespace {
- from_index(index);
+ void KPKPosition::classify_leaf(unsigned idx) {
- // Check if two pieces are on the same square
- if ( whiteKingSquare == pawnSquare
- || whiteKingSquare == blackKingSquare
- || blackKingSquare == pawnSquare)
- return RESULT_INVALID;
+ stm = Color(idx & 1);
+ bksq = Square((idx >> 1) & 0x3F);
+ wksq = Square((idx >> 7) & 0x3F);
+ psq = File((idx >> 13) & 3) | Rank(6 - (idx >> 15));
- // Check if a king can be captured
- if ( (wk_attacks() & blackKingSquare)
- || ((pawn_attacks() & blackKingSquare) && sideToMove == WHITE))
- 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 && (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.
- if ( rank_of(pawnSquare) == RANK_7
- && sideToMove == WHITE
- && whiteKingSquare != pawnSquare + DELTA_N
- && ( square_distance(blackKingSquare, pawnSquare + DELTA_N) > 1
- || (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.
+ 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
- if ( sideToMove == BLACK
- && !(bk_attacks() & ~(wk_attacks() | pawn_attacks())))
- return RESULT_DRAW;
+ else if ( stm == BLACK
+ && !(k_attacks<BLACK>() & ~(k_attacks<WHITE>() | StepAttacksBB[PAWN][psq])))
+ res = DRAW;
- // Case 2: King can capture pawn
- if ( sideToMove == BLACK
- && (bk_attacks() & pawnSquare) && !(wk_attacks() & pawnSquare))
- return RESULT_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
- if ( blackKingSquare == pawnSquare + DELTA_N
- && rank_of(pawnSquare) < RANK_7)
- return RESULT_DRAW;
+ 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
- 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
+ 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
- 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];
+ 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;
+
+ else
+ res = UNKNOWN;
}
- Result KPKPosition::classify_white(const Result db[]) {
+ template<Color Us>
+ Result KPKPosition::classify(const std::vector<KPKPosition>& 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.
+ // 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(BLACK, bksq, pop_lsb(&b), psq)]
+ : db[index(WHITE, pop_lsb(&b), wksq, psq)];
- if (r == RESULT_WIN)
- return RESULT_WIN;
+ if (Us == WHITE && (r & WIN))
+ return res = WIN;
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
+ if (Us == BLACK && (r & DRAW))
+ return res = 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(BLACK, bksq, wksq, s)]; // 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(BLACK, bksq, wksq, s + DELTA_N)]; // Double push
- if (r == RESULT_WIN)
- return RESULT_WIN;
-
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
- }
+ if (r & WIN)
+ return res = 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)];
-
- if (r == RESULT_DRAW)
- return RESULT_DRAW;
-
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
- }
- return unknownFound ? RESULT_UNKNOWN : RESULT_WIN;
+ return res = r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN;
}
}
projects / stockfish / blobdiff