*/
#include <cassert>
+#include <vector>
#include "bitboard.h"
#include "types.h"
namespace {
+ // 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 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,
struct KPKPosition {
- Result classify_leaf(int idx);
- Result classify(int idx, Result db[]);
+ void classify_leaf(unsigned idx);
- private:
- template<Color Us> Result classify(const Result db[]) const;
+ Result classify(const std::vector<KPKPosition>& db)
+ { return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
- template<Color Us> Bitboard k_attacks() const {
- return Us == WHITE ? StepAttacksBB[W_KING][wksq] : StepAttacksBB[B_KING][bksq];
- }
+ operator Result() const { return res; }
- Bitboard p_attacks() const { return StepAttacksBB[W_PAWN][psq]; }
- void decode_index(int idx);
+ private:
+ template<Color Us> Bitboard k_attacks() const
+ { return StepAttacksBB[KING][Us == WHITE ? wksq : bksq]; }
+
+ template<Color Us> Result classify(const std::vector<KPKPosition>& db);
- Square wksq, bksq, psq;
Color stm;
+ Square bksq, wksq, psq;
+ Result res;
};
- // 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
-
- // Each uint32_t stores results of 32 positions, one per bit
- uint32_t KPKBitbase[IndexMax / 32];
+} // namespace
- int index(Square wksq, Square bksq, Square psq, Color stm);
-}
+bool Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
-uint32_t Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
+ assert(file_of(wpsq) <= FILE_D);
- int idx = index(wksq, bksq, wpsq, stm);
+ unsigned idx = index(stm, bksq, wksq, wpsq);
return KPKBitbase[idx / 32] & (1 << (idx & 31));
}
void Bitbases::init_kpk() {
- Result* db = new Result[IndexMax]; // Avoid to hit stack limit on some platforms
- KPKPosition pos;
- int idx, bit, repeat = 1;
+ unsigned idx, repeat = 1;
+ std::vector<KPKPosition> db(IndexMax);
- // Initialize table with known win / draw positions
+ // Initialize db with known win / draw positions
for (idx = 0; idx < IndexMax; idx++)
- db[idx] = pos.classify_leaf(idx);
+ db[idx].classify_leaf(idx);
- // Iterate until all positions are classified (30 cycles needed)
+ // Iterate until all positions are classified (26 cycles needed)
while (repeat)
for (repeat = idx = 0; idx < IndexMax; idx++)
- if (db[idx] == UNKNOWN && (db[idx] = pos.classify(idx, db)) != UNKNOWN)
+ if (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN)
repeat = 1;
- // 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;
-
- delete [] db;
+ // Map 32 results into one KPKBitbase[] entry
+ for (idx = 0; idx < IndexMax; idx++)
+ if (db[idx] == WIN)
+ KPKBitbase[idx / 32] |= 1 << (idx & 31);
}
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)
-
- int index(Square w, Square b, Square p, Color c) {
-
- assert(file_of(p) <= FILE_D);
-
- return c + (b << 1) + (w << 7) + (file_of(p) << 13) + ((rank_of(p) - 1) << 15);
- }
-
- void KPKPosition::decode_index(int idx) {
+ void KPKPosition::classify_leaf(unsigned idx) {
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) {
-
- decode_index(idx);
+ bksq = Square((idx >> 1) & 0x3F);
+ wksq = Square((idx >> 7) & 0x3F);
+ psq = File((idx >> 13) & 3) | Rank(6 - (idx >> 15));
// 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;
+ || (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(psq) == RANK_7
- && stm == WHITE
- && wksq != psq + DELTA_N
- && ( square_distance(bksq, psq + DELTA_N) > 1
- ||(k_attacks<WHITE>() & (psq + DELTA_N))))
- return WIN;
+ 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 ( stm == BLACK
- && !(k_attacks<BLACK>() & ~(k_attacks<WHITE>() | p_attacks())))
- return DRAW;
+ else if ( stm == BLACK
+ && !(k_attacks<BLACK>() & ~(k_attacks<WHITE>() | StepAttacksBB[PAWN][psq])))
+ res = DRAW;
// Case 2: King can capture undefended pawn
- if ( stm == BLACK
- && (k_attacks<BLACK>() & psq & ~k_attacks<WHITE>()))
- return DRAW;
+ else if ( stm == BLACK
+ && (k_attacks<BLACK>() & psq & ~k_attacks<WHITE>()))
+ res = DRAW;
// Case 3: Black king in front of white pawn
- if ( bksq == psq + DELTA_N
- && rank_of(psq) < RANK_7)
- return 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 ( stm == WHITE
- && wksq == psq + DELTA_N
- && bksq == wksq + DELTA_N + DELTA_N
- && rank_of(psq) < RANK_5)
- return DRAW;
+ 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 ( bksq == SQ_A8
- && file_of(psq) == FILE_A)
- return DRAW;
+ else if ( bksq == SQ_A8
+ && file_of(psq) == FILE_A)
+ res = 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;
+ 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;
}
template<Color Us>
- Result KPKPosition::classify(const Result db[]) const {
+ Result KPKPosition::classify(const std::vector<KPKPosition>& db) {
// 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
while (b)
{
- r |= Us == WHITE ? db[index(pop_lsb(&b), bksq, psq, BLACK)]
- : db[index(wksq, pop_lsb(&b), psq, WHITE)];
+ r |= Us == WHITE ? db[index(BLACK, bksq, pop_lsb(&b), psq)]
+ : db[index(WHITE, pop_lsb(&b), wksq, psq)];
if (Us == WHITE && (r & WIN))
- return WIN;
+ return res = WIN;
if (Us == BLACK && (r & DRAW))
- return DRAW;
+ return res = DRAW;
}
if (Us == WHITE && rank_of(psq) < RANK_7)
{
Square s = psq + DELTA_N;
- r |= db[index(wksq, bksq, s, BLACK)]; // Single push
+ r |= db[index(BLACK, bksq, wksq, s)]; // Single push
if (rank_of(s) == RANK_3 && s != wksq && s != bksq)
- r |= db[index(wksq, bksq, s + DELTA_N, BLACK)]; // Double push
+ r |= db[index(BLACK, bksq, wksq, s + DELTA_N)]; // Double push
if (r & WIN)
- return WIN;
+ return res = WIN;
}
- return r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN;
- }
-
- Result KPKPosition::classify(int idx, Result db[]) {
-
- decode_index(idx);
- return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db);
+ return res = r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN;
}
}
projects / stockfish / commitdiff