/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2008-2013 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 {
// 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
+ const unsigned IndexMax = 2*24*64*64; // stm * psq * wksq * bksq = 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
+ // Information is mapped in a way that minimizes number of iterations:
//
- // 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 0- 5: white king square (from SQ_A1 to SQ_H8)
+ // bit 6-11: black king square (from SQ_A1 to SQ_H8)
+ // bit 12: side to move (WHITE or BLACK)
// 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);
+ // bit 15-17: white pawn RANK_7 - rank (from RANK_7 - RANK_7 to RANK_7 - RANK_2)
+ unsigned index(Color us, Square bksq, Square wksq, Square psq) {
+ return wksq + (bksq << 6) + (us << 12) + (file_of(psq) << 13) + ((RANK_7 - rank_of(psq)) << 15);
}
enum Result {
struct KPKPosition {
- void classify_leaf(unsigned idx);
-
- Result classify(const std::vector<KPKPosition>& db)
- { return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
-
operator Result() const { return res; }
+ Result classify_leaf(unsigned idx);
+ Result classify(const std::vector<KPKPosition>& db)
+ { return us == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
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);
- Color stm;
+ Color us;
Square bksq, wksq, psq;
Result res;
};
} // namespace
-bool Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
+bool Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color us) {
assert(file_of(wpsq) <= FILE_D);
- unsigned idx = index(stm, bksq, wksq, wpsq);
- return KPKBitbase[idx / 32] & (1 << (idx & 31));
+ unsigned idx = index(us, bksq, wksq, wpsq);
+ return KPKBitbase[idx / 32] & (1 << (idx & 0x1F));
}
for (idx = 0; idx < IndexMax; idx++)
db[idx].classify_leaf(idx);
- // Iterate until all positions are classified (26 cycles needed)
+ // Iterate through the positions until no more of the unknown positions can be
+ // changed to either wins or draws (15 cycles needed).
while (repeat)
for (repeat = idx = 0; idx < IndexMax; idx++)
if (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN)
// Map 32 results into one KPKBitbase[] entry
for (idx = 0; idx < IndexMax; idx++)
if (db[idx] == WIN)
- KPKBitbase[idx / 32] |= 1 << (idx & 31);
+ KPKBitbase[idx / 32] |= 1 << (idx & 0x1F);
}
namespace {
- void KPKPosition::classify_leaf(unsigned idx) {
+ Result 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(6 - (idx >> 15));
+ wksq = Square((idx >> 0) & 0x3F);
+ bksq = Square((idx >> 6) & 0x3F);
+ us = Color ((idx >> 12) & 0x01);
+ psq = File ((idx >> 13) & 0x03) | Rank(RANK_7 - (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 && (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;
+ || (StepAttacksBB[KING][wksq] & bksq)
+ || (us == WHITE && (StepAttacksBB[PAWN][psq] & bksq)))
+ return res = INVALID;
- else
- res = UNKNOWN;
+ if (us == WHITE)
+ {
+ // Immediate win if pawn can be promoted without getting captured
+ if ( rank_of(psq) == RANK_7
+ && wksq != psq + DELTA_N
+ && ( square_distance(bksq, psq + DELTA_N) > 1
+ ||(StepAttacksBB[KING][wksq] & (psq + DELTA_N))))
+ return res = WIN;
+ }
+ // Immediate draw if is stalemate or king captures undefended pawn
+ else if ( !(StepAttacksBB[KING][bksq] & ~(StepAttacksBB[KING][wksq] | StepAttacksBB[PAWN][psq]))
+ || (StepAttacksBB[KING][bksq] & psq & ~StepAttacksBB[KING][wksq]))
+ return res = DRAW;
+
+ return res = UNKNOWN;
}
template<Color Us>
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
- // 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 WIN, the result
+ // of the current position is WIN. If all moves lead to positions classified
+ // as DRAW, the current position is classified DRAW otherwise the current
+ // position is classified as 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.
+ // Black to Move: If one move leads to a position classified as DRAW, the result
+ // of the current position is DRAW. If all moves lead to positions classified
+ // as WIN, the position is classified WIN otherwise the current position is
+ // classified UNKNOWN.
+
+ const Color Them = (Us == WHITE ? BLACK : WHITE);
Result r = INVALID;
- Bitboard b = k_attacks<Us>();
+ Bitboard b = StepAttacksBB[KING][Us == WHITE ? wksq : bksq];
while (b)
- {
- 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 res = WIN;
-
- if (Us == BLACK && (r & DRAW))
- return res = DRAW;
- }
+ r |= Us == WHITE ? db[index(Them, bksq, pop_lsb(&b), psq)]
+ : db[index(Them, pop_lsb(&b), wksq, psq)];
if (Us == WHITE && rank_of(psq) < RANK_7)
{
if (rank_of(s) == RANK_3 && s != wksq && s != bksq)
r |= db[index(BLACK, bksq, wksq, s + DELTA_N)]; // Double push
-
- if (r & WIN)
- return res = WIN;
}
- return res = r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN;
+ if (Us == WHITE)
+ return res = r & WIN ? WIN : r & UNKNOWN ? UNKNOWN : DRAW;
+ else
+ return res = r & DRAW ? DRAW : r & UNKNOWN ? UNKNOWN : WIN;
}
-}
+} // namespace
projects / stockfish / blobdiff