bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
+
bool fail_high_ply_1();
int current_search_time();
int nps();
Move ttMove = (tte ? tte->move() : MOVE_NONE);
- // Go with internal iterative deepening if we don't have a TT move.
+ // Go with internal iterative deepening if we don't have a TT move
if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
{
search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
ss[ply].currentMoveCaptureValue = move_is_ep(move) ?
PawnValueMidgame : pos.midgame_value_of_piece_on(move_to(move));
- // Decide the new search depth.
+ // Decide the new search depth
Depth ext = extension(pos, move, true, moveIsCheck, singleReply, mateThreat);
Depth newDepth = depth - OnePly + ext;
- // Make and search the move.
+ // Make and search the move
UndoInfo u;
pos.do_move(move, u, dcCandidates);
// Split?
if ( ActiveThreads > 1
- && bestValue < beta && depth >= MinimumSplitDepth
- && Iteration <= 99 && idle_thread_exists(threadID)
- && !AbortSearch && !thread_should_stop(threadID)
+ && bestValue < beta
+ && depth >= MinimumSplitDepth
+ && Iteration <= 99
+ && idle_thread_exists(threadID)
+ && !AbortSearch
+ && !thread_should_stop(threadID)
&& split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
&moveCount, &mp, dcCandidates, threadID, true))
break;
Move m = ss[ply].pv[ply];
if (pos.square_is_empty(move_to(m)) && !move_promotion(m) && !move_is_ep(m))
{
- for(int i = 0; i < moveCount - 1; i++)
- if( pos.square_is_empty(move_to(movesSearched[i]))
- && !move_promotion(movesSearched[i])
- && !move_is_ep(movesSearched[i]))
+ for (int i = 0; i < moveCount - 1; i++)
+ if ( pos.square_is_empty(move_to(movesSearched[i]))
+ && !move_promotion(movesSearched[i])
+ && !move_is_ep(movesSearched[i]))
H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
H.success(pos.piece_on(move_from(m)), m, depth);
Value search(Position &pos, SearchStack ss[], Value beta, Depth depth,
int ply, bool allowNullmove, int threadID) {
+
assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
assert(ply >= 0 && ply < PLY_MAX);
assert(threadID >= 0 && threadID < ActiveThreads);
// Initialize, and make an early exit in case of an aborted search,
// an instant draw, maximum ply reached, etc.
- if(AbortSearch || thread_should_stop(threadID))
- return Value(0);
+ if (AbortSearch || thread_should_stop(threadID))
+ return Value(0);
- if(depth < OnePly)
- return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
+ if (depth < OnePly)
+ return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
init_node(pos, ss, ply, threadID);
- if(pos.is_draw())
- return VALUE_DRAW;
+ if (pos.is_draw())
+ return VALUE_DRAW;
- if(ply >= PLY_MAX - 1)
- return evaluate(pos, ei, threadID);
+ if (ply >= PLY_MAX - 1)
+ return evaluate(pos, ei, threadID);
// Mate distance pruning
- if(value_mated_in(ply) >= beta)
- return beta;
- if(value_mate_in(ply+1) < beta)
- return beta-1;
+ if (value_mated_in(ply) >= beta)
+ return beta;
+ if (value_mate_in(ply + 1) < beta)
+ return beta - 1;
// Transposition table lookup
const TTEntry* tte = TT.retrieve(pos);
bool mateThreat = false;
// Null move search
- if(!pos.is_check() && allowNullmove && ok_to_do_nullmove(pos)
- && approximateEval >= beta - NullMoveMargin) {
- UndoInfo u;
- Value nullValue;
-
- ss[ply].currentMove = MOVE_NULL;
- pos.do_null_move(u);
- nullValue = -search(pos, ss, -(beta-1), depth-4*OnePly, ply+1, false,
- threadID);
- pos.undo_null_move(u);
-
- if(nullValue >= beta) {
- if(depth >= 6 * OnePly) { // Do zugzwang verification search
- Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
- if(v >= beta)
- return beta;
+ if ( allowNullmove
+ && !pos.is_check()
+ && ok_to_do_nullmove(pos)
+ && approximateEval >= beta - NullMoveMargin)
+ {
+ ss[ply].currentMove = MOVE_NULL;
+
+ UndoInfo u;
+ pos.do_null_move(u);
+ Value nullValue = -search(pos, ss, -(beta-1), depth-4*OnePly, ply+1, false, threadID);
+ pos.undo_null_move(u);
+
+ if (nullValue >= beta)
+ {
+ if (depth < 6 * OnePly)
+ return beta;
+
+ // Do zugzwang verification search
+ Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
+ if (v >= beta)
+ return beta;
+ } 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
+ // low score (which will cause the reduced move to fail high in the
+ // parent node, which will trigger a re-search with full depth).
+ if (nullValue == value_mated_in(ply + 2))
+ mateThreat = true;
+
+ ss[ply].threatMove = ss[ply + 1].currentMove;
+ if ( depth < ThreatDepth
+ && ss[ply - 1].reduction
+ && connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
+ return beta - 1;
}
- else
- return beta;
- }
- 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
- // low score (which will cause the reduced move to fail high in the
- // parent node, which will trigger a re-search with full depth).
- if(nullValue == value_mated_in(ply+2))
- mateThreat = true;
- ss[ply].threatMove = ss[ply+1].currentMove;
- if(depth < ThreatDepth && ss[ply-1].reduction &&
- connected_moves(pos, ss[ply-1].currentMove, ss[ply].threatMove))
- return beta - 1;
- }
}
- // Razoring:
- else if(depth < RazorDepth && approximateEval < beta - RazorMargin &&
- evaluate(pos, ei, threadID) < beta - RazorMargin) {
- Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
- if(v < beta)
- return v;
+ // Null move search not allowed, try razoring
+ else if ( depth < RazorDepth
+ && approximateEval < beta - RazorMargin
+ && evaluate(pos, ei, threadID) < beta - RazorMargin)
+ {
+ Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
+ if (v < beta)
+ return v;
}
- // Internal iterative deepening
- if(UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
- evaluate(pos, ei, threadID) >= beta - IIDMargin) {
- search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
- ttMove = ss[ply].pv[ply];
+ // Go with internal iterative deepening if we don't have a TT move
+ if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
+ evaluate(pos, ei, threadID) >= beta - IIDMargin)
+ {
+ search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
+ ttMove = ss[ply].pv[ply];
}
// Initialize a MovePicker object for the current position, and prepare
// to search all moves:
MovePicker mp = MovePicker(pos, false, ttMove, ss[ply].mateKiller,
ss[ply].killer1, ss[ply].killer2, depth);
+
Move move, movesSearched[256];
int moveCount = 0;
- Value value, bestValue = -VALUE_INFINITE, futilityValue = VALUE_NONE;
+ Value value, bestValue = -VALUE_INFINITE;
Bitboard dcCandidates = mp.discovered_check_candidates();
+ Value futilityValue = VALUE_NONE;
bool isCheck = pos.is_check();
- bool useFutilityPruning =
- UseFutilityPruning && depth < SelectiveDepth && !isCheck;
+ bool useFutilityPruning = UseFutilityPruning
+ && depth < SelectiveDepth
+ && !isCheck;
// Loop through all legal moves until no moves remain or a beta cutoff
// occurs.
- while(bestValue < beta && !thread_should_stop(threadID)
- && (move = mp.get_next_move()) != MOVE_NONE) {
- UndoInfo u;
- Depth ext, newDepth;
+ while( bestValue < beta
+ && (move = mp.get_next_move()) != MOVE_NONE
+ && !thread_should_stop(threadID))
+ {
+ assert(move_is_ok(move));
+
bool singleReply = (isCheck && mp.number_of_moves() == 1);
bool moveIsCheck = pos.move_is_check(move, dcCandidates);
bool moveIsCapture = pos.move_is_capture(move);
bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
- assert(move_is_ok(move));
movesSearched[moveCount++] = ss[ply].currentMove = move;
- // Decide the new search depth.
- ext = extension(pos, move, false, moveIsCheck, singleReply, mateThreat);
- newDepth = depth - OnePly + ext;
+ // Decide the new search depth
+ Depth ext = extension(pos, move, false, moveIsCheck, singleReply, mateThreat);
+ Depth newDepth = depth - OnePly + ext;
// Futility pruning
- if(useFutilityPruning && ext == Depth(0) && !moveIsCapture &&
- !moveIsPassedPawnPush && !move_promotion(move)) {
-
- if(moveCount >= 2 + int(depth)
- && ok_to_prune(pos, move, ss[ply].threatMove, depth))
- continue;
+ if ( useFutilityPruning
+ && ext == Depth(0)
+ && !moveIsCapture
+ && !moveIsPassedPawnPush
+ && !move_promotion(move))
+ {
+ if ( moveCount >= 2 + int(depth)
+ && ok_to_prune(pos, move, ss[ply].threatMove, depth))
+ continue;
- if(depth < 3 * OnePly && approximateEval < beta) {
- if(futilityValue == VALUE_NONE)
- futilityValue = evaluate(pos, ei, threadID)
- + ((depth < 2 * OnePly)? FutilityMargin1 : FutilityMargin2);
- if(futilityValue < beta) {
- if(futilityValue > bestValue)
- bestValue = futilityValue;
- continue;
+ if (depth < 3 * OnePly && approximateEval < beta)
+ {
+ if (futilityValue == VALUE_NONE)
+ futilityValue = evaluate(pos, ei, threadID) + (depth < 2 * OnePly ? FutilityMargin1 : FutilityMargin2);
+
+ if (futilityValue < beta)
+ {
+ if(futilityValue > bestValue)
+ bestValue = futilityValue;
+ continue;
+ }
}
- }
}
- // Make and search the move.
+ // Make and search the move
+ UndoInfo u;
pos.do_move(move, u, dcCandidates);
- if(depth >= 2*OnePly && ext == Depth(0) && moveCount >= LMRNonPVMoves
- && !moveIsCapture && !move_promotion(move) && !moveIsPassedPawnPush
- && !move_is_castle(move)
- && move != ss[ply].killer1 && move != ss[ply].killer2) {
- ss[ply].reduction = OnePly;
- value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true,
- threadID);
+ // Try to reduce non-pv search depth by one ply if move seems not problematic,
+ // if the move fails high will be re-searched at full depth.
+ if ( depth >= 2*OnePly
+ && ext == Depth(0)
+ && moveCount >= LMRNonPVMoves
+ && !moveIsCapture
+ && !move_promotion(move)
+ && !moveIsPassedPawnPush
+ && !move_is_castle(move)
+ && move != ss[ply].killer1
+ && move != ss[ply].killer2)
+ {
+ ss[ply].reduction = OnePly;
+ value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
}
else
- value = beta;
- if(value >= beta) {
- ss[ply].reduction = Depth(0);
- value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
+ value = beta; // Just to trigger next condition
+
+ if (value >= beta) // Go with full depth non-pv search
+ {
+ ss[ply].reduction = Depth(0);
+ value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
}
pos.undo_move(move, u);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// New best move?
- if(value > bestValue) {
+ if (value > bestValue)
+ {
bestValue = value;
- if(value >= beta)
- update_pv(ss, ply);
- if(value == value_mate_in(ply + 1))
- ss[ply].mateKiller = move;
+ if (value >= beta)
+ update_pv(ss, ply);
+ if (value == value_mate_in(ply + 1))
+ ss[ply].mateKiller = move;
}
// Split?
- if(ActiveThreads > 1 && bestValue < beta && depth >= MinimumSplitDepth
- && Iteration <= 99 && idle_thread_exists(threadID)
- && !AbortSearch && !thread_should_stop(threadID)
+ if( ActiveThreads > 1
+ && bestValue < beta
+ && depth >= MinimumSplitDepth
+ && Iteration <= 99
+ && idle_thread_exists(threadID)
+ && !AbortSearch
+ && !thread_should_stop(threadID)
&& split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
&mp, dcCandidates, threadID, false))
break;
// All legal moves have been searched. A special case: If there were
// no legal moves, it must be mate or stalemate:
- if(moveCount == 0) {
- if(pos.is_check())
- return value_mated_in(ply);
- else
- return VALUE_DRAW;
- }
+ if (moveCount == 0)
+ return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
// If the search is not aborted, update the transposition table,
// history counters, and killer moves. This code is somewhat messy,
// and definitely needs to be cleaned up. FIXME
- if(!AbortSearch && !thread_should_stop(threadID)) {
- if(bestValue < beta)
- TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE,
- VALUE_TYPE_UPPER);
- else {
+ if (AbortSearch || thread_should_stop(threadID))
+ return bestValue;
+
+ if (bestValue < beta)
+ TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_UPPER);
+ else
+ {
Move m = ss[ply].pv[ply];
+ if (pos.square_is_empty(move_to(m)) && !move_promotion(m) && !move_is_ep(m))
+ {
+ for (int i = 0; i < moveCount - 1; i++)
+ if ( pos.square_is_empty(move_to(movesSearched[i]))
+ && !move_promotion(movesSearched[i])
+ && !move_is_ep(movesSearched[i]))
+ H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
- if(pos.square_is_empty(move_to(m)) && !move_promotion(m) &&
- !move_is_ep(m)) {
- for(int i = 0; i < moveCount - 1; i++)
- if(pos.square_is_empty(move_to(movesSearched[i]))
- && !move_promotion(movesSearched[i])
- && !move_is_ep(movesSearched[i]))
- H.failure(pos.piece_on(move_from(movesSearched[i])),
- movesSearched[i]);
- H.success(pos.piece_on(move_from(m)), m, depth);
-
- if(m != ss[ply].killer1) {
- ss[ply].killer2 = ss[ply].killer1;
- ss[ply].killer1 = m;
- }
+ H.success(pos.piece_on(move_from(m)), m, depth);
+
+ if (m != ss[ply].killer1)
+ {
+ ss[ply].killer2 = ss[ply].killer1;
+ ss[ply].killer1 = m;
+ }
}
TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
- }
}
-
return bestValue;
}
lock_release(&(sp->lock));
}
+
// ok_to_use_TT() returns true if a transposition table score
// can be used at a given point in search.
|| (is_upper_bound(tte->type()) && v < beta));
}
+
/// The RootMove class
// Constructor