Value value_to_tt(Value v, int ply);
Value value_from_tt(Value v, int ply);
bool check_is_dangerous(const Position& pos, Move move, Value futilityBase, Value beta);
- bool allows(const Position& pos, Move first, Move second);
bool refutes(const Position& pos, Move first, Move second);
string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
assert(PvNode || (alpha == beta - 1));
assert(depth > DEPTH_ZERO);
- Move movesSearched[64];
+ Move quietsSearched[64];
StateInfo st;
const TTEntry *tte;
SplitPoint* splitPoint;
Value eval, nullValue, futilityValue;
bool inCheck, givesCheck, pvMove, singularExtensionNode;
bool captureOrPromotion, dangerous, doFullDepthSearch;
- int moveCount, playedMoveCount;
+ int moveCount, quietCount;
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
- moveCount = playedMoveCount = 0;
+ moveCount = quietCount = 0;
inCheck = pos.checkers();
if (SpNode)
// Step 5. Evaluate the position statically and update parent's gain statistics
if (inCheck)
+ {
ss->staticEval = ss->evalMargin = eval = VALUE_NONE;
+ goto iid_start;
+ }
else if (tte)
{
// Update gain for the parent non-capture move given the static position
// evaluation before and after the move.
- if ( (move = (ss-1)->currentMove) != MOVE_NULL
- && (ss-1)->staticEval != VALUE_NONE
+ if ( !pos.captured_piece_type()
&& ss->staticEval != VALUE_NONE
- && !pos.captured_piece_type()
+ && (ss-1)->staticEval != VALUE_NONE
+ && (move = (ss-1)->currentMove) != MOVE_NULL
&& type_of(move) == NORMAL)
{
Square to = to_sq(move);
// Step 6. Razoring (is omitted in PV nodes)
if ( !PvNode
&& depth < 4 * ONE_PLY
- && !inCheck
&& eval + razor_margin(depth) < beta
&& ttMove == MOVE_NONE
&& abs(beta) < VALUE_MATE_IN_MAX_PLY
if ( !PvNode
&& !ss->skipNullMove
&& depth < 4 * ONE_PLY
- && !inCheck
&& eval - futility_margin(depth, (ss-1)->futilityMoveCount) >= beta
&& abs(beta) < VALUE_MATE_IN_MAX_PLY
&& abs(eval) < VALUE_KNOWN_WIN
if ( !PvNode
&& !ss->skipNullMove
&& depth > ONE_PLY
- && !inCheck
&& eval >= beta
&& abs(beta) < VALUE_MATE_IN_MAX_PLY
&& pos.non_pawn_material(pos.side_to_move()))
else
{
// The null move failed low, which means that we may be faced with
- // some kind of threat. If the previous move was reduced, check if
- // the move that refuted the null move was somehow connected to the
- // move which was reduced. If a connection is found, return a fail
+ // some kind of threat. If the previous move was reduced return a fail
// low score (which will cause the reduced move to fail high in the
// parent node, which will trigger a re-search with full depth).
- threatMove = (ss+1)->currentMove;
-
if ( depth < 5 * ONE_PLY
&& (ss-1)->reduction
- && threatMove != MOVE_NONE
- && allows(pos, (ss-1)->currentMove, threatMove))
+ && nullValue < beta - Value(128))
return alpha;
+
+ threatMove = (ss+1)->currentMove;
}
}
// prune the previous move.
if ( !PvNode
&& depth >= 5 * ONE_PLY
- && !inCheck
&& !ss->skipNullMove
&& abs(beta) < VALUE_MATE_IN_MAX_PLY)
{
}
}
+iid_start: // When in check we skip early cut tests
+
// Step 10. Internal iterative deepening
if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
&& ttMove == MOVE_NONE
givesCheck = pos.move_gives_check(move, ci);
dangerous = givesCheck
|| pos.is_passed_pawn_push(move)
- || type_of(move) == CASTLE
- || ( captureOrPromotion // Entering a pawn endgame?
- && type_of(pos.piece_on(to_sq(move))) != PAWN
- && type_of(move) == NORMAL
- && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
- - PieceValue[MG][pos.piece_on(to_sq(move))] == VALUE_ZERO));
+ || type_of(move) == CASTLE;
// Step 12. Extend checks and, in PV nodes, also dangerous moves
if (PvNode && dangerous)
pvMove = PvNode && moveCount == 1;
ss->currentMove = move;
- if (!SpNode && !captureOrPromotion && playedMoveCount < 64)
- movesSearched[playedMoveCount++] = move;
+ if (!SpNode && !captureOrPromotion && quietCount < 64)
+ quietsSearched[quietCount++] = move;
// Step 14. Make the move
pos.do_move(move, st, ci, givesCheck);
// If we have pruned all the moves without searching return a fail-low score
if (bestValue == -VALUE_INFINITE)
- {
- assert(!playedMoveCount);
-
bestValue = alpha;
- }
- if (bestValue >= beta) // Failed high
+ TT.store(posKey, value_to_tt(bestValue, ss->ply),
+ bestValue >= beta ? BOUND_LOWER :
+ PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
+ depth, bestMove, ss->staticEval, ss->evalMargin);
+
+ // Quiet best move: update killers, history and countermoves
+ if ( bestValue >= beta
+ && !pos.is_capture_or_promotion(bestMove)
+ && !inCheck)
{
- TT.store(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER, depth,
- bestMove, ss->staticEval, ss->evalMargin);
-
- if (!pos.is_capture_or_promotion(bestMove) && !inCheck)
+ if (ss->killers[0] != bestMove)
{
- if (bestMove != ss->killers[0])
- {
- ss->killers[1] = ss->killers[0];
- ss->killers[0] = bestMove;
- }
-
- // Increase history value of the cut-off move
- Value bonus = Value(int(depth) * int(depth));
- History.update(pos.piece_moved(bestMove), to_sq(bestMove), bonus);
- if (is_ok((ss-1)->currentMove))
- Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, bestMove);
+ ss->killers[1] = ss->killers[0];
+ ss->killers[0] = bestMove;
+ }
- // Decrease history of all the other played non-capture moves
- for (int i = 0; i < playedMoveCount - 1; i++)
- {
- Move m = movesSearched[i];
- History.update(pos.piece_moved(m), to_sq(m), -bonus);
- }
+ // Increase history value of the cut-off move and decrease all the other
+ // played non-capture moves.
+ Value bonus = Value(int(depth) * int(depth));
+ History.update(pos.piece_moved(bestMove), to_sq(bestMove), bonus);
+ for (int i = 0; i < quietCount - 1; i++)
+ {
+ Move m = quietsSearched[i];
+ History.update(pos.piece_moved(m), to_sq(m), -bonus);
}
+
+ if (is_ok((ss-1)->currentMove))
+ Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, bestMove);
}
- else // Failed low or PV search
- TT.store(posKey, value_to_tt(bestValue, ss->ply),
- PvNode && bestMove != MOVE_NONE ? BOUND_EXACT : BOUND_UPPER,
- depth, bestMove, ss->staticEval, ss->evalMargin);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
: DEPTH_QS_NO_CHECKS;
- // Transposition table lookup. At PV nodes, we don't use the TT for
- // pruning, but only for move ordering.
+ // Transposition table lookup
posKey = pos.key();
tte = TT.probe(posKey);
ttMove = tte ? tte->move() : MOVE_NONE;
}
- // allows() tests whether the 'first' move at previous ply somehow makes the
- // 'second' move possible, for instance if the moving piece is the same in
- // both moves. Normally the second move is the threat (the best move returned
- // from a null search that fails low).
-
- bool allows(const Position& pos, Move first, Move second) {
-
- assert(is_ok(first));
- assert(is_ok(second));
- assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
- assert(color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
-
- Square m1from = from_sq(first);
- Square m2from = from_sq(second);
- Square m1to = to_sq(first);
- Square m2to = to_sq(second);
-
- // The piece is the same or second's destination was vacated by the first move
- if (m1to == m2from || m2to == m1from)
- return true;
-
- // Second one moves through the square vacated by first one
- if (between_bb(m2from, m2to) & m1from)
- return true;
-
- // Second's destination is defended by the first move's piece
- Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
- if (m1att & m2to)
- return true;
-
- // Second move gives a discovered check through the first's checking piece
- if (m1att & pos.king_square(pos.side_to_move()))
- {
- assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);
- return true;
- }
-
- return false;
- }
-
-
// refutes() tests whether a 'first' move is able to defend against a 'second'
// opponent's move. In this case will not be pruned. Normally the second move
// is the threat (the best move returned from a null search that fails low).
projects / stockfish / blobdiff