kate/BadFish
1
0
Fork 0
mirror of https://github.com/sockspls/badfish synced 2025-04-30 00:33:09 +00:00
Code Issues Releases Wiki Activity

Unite search_pv() and search()

Browse source 
A lot of redundant code removed: -182 lines of code

No functional and speed change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Joona Kiiski 2010-05-08 11:54:51 +03:00 • committed by Marco Costalba
parent c0334c7bac
commit b075d8ca53
1 changed files with 206 additions and 388 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

590
src/search.cpp
View file

@ -194,8 +194,7 @@ namespace {
Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2]; Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
// Minimum depth for use of singular extension // Minimum depth for use of singular extension
const Depth SingularExtensionDepthAtPVNodes = 6 * OnePly; const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
const Depth SingularExtensionDepthAtNonPVNodes = 8 * OnePly;
// If the TT move is at least SingularExtensionMargin better then the // If the TT move is at least SingularExtensionMargin better then the
// remaining ones we will extend it. // remaining ones we will extend it.
@ -280,8 +279,10 @@ namespace {
Value id_loop(const Position& pos, Move searchMoves[]); Value id_loop(const Position& pos, Move searchMoves[]);
Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr); Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE); template <bool PvNode>
Value search(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove = MOVE_NONE);
Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID); Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
void sp_search(SplitPoint* sp, int threadID); void sp_search(SplitPoint* sp, int threadID);
void sp_search_pv(SplitPoint* sp, int threadID); void sp_search_pv(SplitPoint* sp, int threadID);
@ -869,7 +870,7 @@ namespace {
alpha = -VALUE_INFINITE; alpha = -VALUE_INFINITE;
// Full depth PV search, done on first move or after a fail high // Full depth PV search, done on first move or after a fail high
value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0); value = -search<true>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
} }
else else
{ {
@ -886,7 +887,7 @@ namespace {
if (ss[0].reduction) if (ss[0].reduction)
{ {
// Reduced depth non-pv search using alpha as upperbound // Reduced depth non-pv search using alpha as upperbound
value = -search(pos, ss, -alpha, newDepth-ss[0].reduction, 1, true, 0); value = -search<false>(pos, ss, -(alpha+1), -alpha, newDepth-ss[0].reduction, 1, true, 0);
doFullDepthSearch = (value > alpha); doFullDepthSearch = (value > alpha);
} }
} }
@ -896,12 +897,12 @@ namespace {
{ {
// Full depth non-pv search using alpha as upperbound // Full depth non-pv search using alpha as upperbound
ss[0].reduction = Depth(0); ss[0].reduction = Depth(0);
value = -search(pos, ss, -alpha, newDepth, 1, true, 0); value = -search<false>(pos, ss, -(alpha+1), -alpha, newDepth, 1, true, 0);
// If we are above alpha then research at same depth but as PV // If we are above alpha then research at same depth but as PV
// to get a correct score or eventually a fail high above beta. // to get a correct score or eventually a fail high above beta.
if (value > alpha) if (value > alpha)
value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0); value = -search<true>(pos, ss, -beta, -alpha, newDepth, 1, false, 0);
} }
} }
@ -1023,8 +1024,10 @@ namespace {
// search_pv() is the main search function for PV nodes. // search_pv() is the main search function for PV nodes.
Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, template <bool PvNode>
Depth depth, int ply, int threadID) { Value search(Position& pos, SearchStack ss[], Value alpha, Value beta,
Depth depth, int ply, bool allowNullmove, int threadID, Move excludedMove) {
assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE); assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
assert(beta > alpha && beta <= VALUE_INFINITE); assert(beta > alpha && beta <= VALUE_INFINITE);
@ -1038,10 +1041,12 @@ namespace {
Move ttMove, move; Move ttMove, move;
Depth ext, newDepth; Depth ext, newDepth;
Value bestValue, value, oldAlpha; Value bestValue, value, oldAlpha;
Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous; bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
bool mateThreat = false; bool mateThreat = false;
int moveCount = 0; int moveCount = 0;
bestValue = value = -VALUE_INFINITE; refinedValue = bestValue = value = -VALUE_INFINITE;
oldAlpha = alpha;
if (depth < OnePly) if (depth < OnePly)
return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID); return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
@ -1058,13 +1063,20 @@ namespace {
return VALUE_DRAW; return VALUE_DRAW;
// Step 3. Mate distance pruning // Step 3. Mate distance pruning
oldAlpha = alpha;
alpha = Max(value_mated_in(ply), alpha); alpha = Max(value_mated_in(ply), alpha);
beta = Min(value_mate_in(ply+1), beta); beta = Min(value_mate_in(ply+1), beta);
if (alpha >= beta) if (alpha >= beta)
return alpha; return alpha;
// Step 4. Transposition table lookup // Step 4. Transposition table lookup
// We don't want the score of a partial search to overwrite a previous full search
// TT value, so we use a different position key in case of an excluded move exists.
Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
tte = TT.retrieve(posKey);
ttMove = (tte ? tte->move() : MOVE_NONE);
// At PV nodes, we don't use the TT for pruning, but only for move ordering. // At PV nodes, we don't use the TT for pruning, but only for move ordering.
// This is to avoid problems in the following areas: // This is to avoid problems in the following areas:
// //
@ -1072,57 +1084,173 @@ namespace {
// * Fifty move rule detection // * Fifty move rule detection
// * Searching for a mate // * Searching for a mate
// * Printing of full PV line // * Printing of full PV line
tte = TT.retrieve(pos.get_key());
ttMove = (tte ? tte->move() : MOVE_NONE); if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
{
// Refresh tte entry to avoid aging
TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove);
ss[ply].currentMove = ttMove; // Can be MOVE_NONE
return value_from_tt(tte->value(), ply);
}
// Step 5. Evaluate the position statically // Step 5. Evaluate the position statically
// At PV nodes we do this only to update gain statistics // At PV nodes we do this only to update gain statistics
isCheck = pos.is_check(); isCheck = pos.is_check();
if (!isCheck) if (!isCheck)
{ {
if (!PvNode && tte && (tte->type() & VALUE_TYPE_EVAL))
ss[ply].eval = value_from_tt(tte->value(), ply);
else
ss[ply].eval = evaluate(pos, ei, threadID); ss[ply].eval = evaluate(pos, ei, threadID);
refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval); update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
} }
// Step 6. Razoring (is omitted in PV nodes) // Step 6. Razoring (is omitted in PV nodes)
// Step 7. Static null move pruning (is omitted in PV nodes) if ( !PvNode
// Step 8. Null move search with verification search (is omitted in PV nodes) && refinedValue < beta - razor_margin(depth)
&& ttMove == MOVE_NONE
// Step 9. Internal iterative deepening && ss[ply - 1].currentMove != MOVE_NULL
if ( depth >= IIDDepthAtPVNodes && depth < RazorDepth
&& ttMove == MOVE_NONE) && !isCheck
&& !value_is_mate(beta)
&& !pos.has_pawn_on_7th(pos.side_to_move()))
{ {
search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID); Value rbeta = beta - razor_margin(depth);
ttMove = ss[ply].pv[ply]; Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
tte = TT.retrieve(pos.get_key()); if (v < rbeta)
// Logically we should return (v + razor_margin(depth)), but
// surprisingly this did slightly weaker in tests.
return v;
} }
// Initialize a MovePicker object for the current position // Step 7. Static null move pruning (is omitted in PV nodes)
// We're betting that the opponent doesn't have a move that will reduce
// the score by more than futility_margin(depth) if we do a null move.
if ( !PvNode
&& allowNullmove
&& depth < RazorDepth
&& !isCheck
&& !value_is_mate(beta)
&& ok_to_do_nullmove(pos)
&& refinedValue >= beta + futility_margin(depth, 0))
return refinedValue - futility_margin(depth, 0);
// Step 8. Null move search with verification search (is omitted in PV nodes)
// When we jump directly to qsearch() we do a null move only if static value is
// at least beta. Otherwise we do a null move if static value is not more than
// NullMoveMargin under beta.
if ( !PvNode
&& allowNullmove
&& depth > OnePly
&& !isCheck
&& !value_is_mate(beta)
&& ok_to_do_nullmove(pos)
&& refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
{
ss[ply].currentMove = MOVE_NULL;
// Null move dynamic reduction based on depth
int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
// Null move dynamic reduction based on value
if (refinedValue - beta > PawnValueMidgame)
R++;
pos.do_null_move(st);
nullValue = -search<false>(pos, ss, -beta, -alpha, depth-R*OnePly, ply+1, false, threadID);
pos.undo_null_move();
if (nullValue >= beta)
{
// Do not return unproven mate scores
if (nullValue >= value_mate_in(PLY_MAX))
nullValue = beta;
if (depth < 6 * OnePly)
return nullValue;
// Do zugzwang verification search
Value v = search<false>(pos, ss, alpha, beta, depth-5*OnePly, ply, false, threadID);
if (v >= beta)
return nullValue;
} 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;
}
}
// Step 9. Internal iterative deepening
// We have different rules for PV nodes and non-pv nodes
if ( PvNode
&& depth >= IIDDepthAtPVNodes
&& ttMove == MOVE_NONE)
{
search<true>(pos, ss, alpha, beta, depth-2*OnePly, ply, false, threadID);
ttMove = ss[ply].pv[ply];
tte = TT.retrieve(posKey);
}
if ( !PvNode
&& depth >= IIDDepthAtNonPVNodes
&& ttMove == MOVE_NONE
&& !isCheck
&& ss[ply].eval >= beta - IIDMargin)
{
search<false>(pos, ss, alpha, beta, depth/2, ply, false, threadID);
ttMove = ss[ply].pv[ply];
tte = TT.retrieve(posKey);
}
// Expensive mate threat detection (only for PV nodes)
if (PvNode)
mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move())); mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
// Initialize a MovePicker object for the current position
MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], (PvNode ? -VALUE_INFINITE : beta));
CheckInfo ci(pos); CheckInfo ci(pos);
// Step 10. Loop through moves // Step 10. Loop through moves
// Loop through all legal moves until no moves remain or a beta cutoff occurs // Loop through all legal moves until no moves remain or a beta cutoff occurs
while ( alpha < beta while ( bestValue < beta
&& (move = mp.get_next_move()) != MOVE_NONE && (move = mp.get_next_move()) != MOVE_NONE
&& !TM.thread_should_stop(threadID)) && !TM.thread_should_stop(threadID))
{ {
assert(move_is_ok(move)); assert(move_is_ok(move));
if (move == excludedMove)
continue;
singleEvasion = (isCheck && mp.number_of_evasions() == 1); singleEvasion = (isCheck && mp.number_of_evasions() == 1);
moveIsCheck = pos.move_is_check(move, ci); moveIsCheck = pos.move_is_check(move, ci);
captureOrPromotion = pos.move_is_capture_or_promotion(move); captureOrPromotion = pos.move_is_capture_or_promotion(move);
// Step 11. Decide the new search depth // Step 11. Decide the new search depth
ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous); ext = extension(pos, move, PvNode, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
// Singular extension search. We extend the TT move if its value is much better than // Singular extension search. We extend the TT move if its value is much better than
// its siblings. To verify this we do a reduced search on all the other moves but the // its siblings. To verify this we do a reduced search on all the other moves but the
// ttMove, if result is lower then ttValue minus a margin then we extend ttMove. // ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
if ( depth >= SingularExtensionDepthAtPVNodes if ( depth >= SingularExtensionDepth[PvNode]
&& tte && tte
&& move == tte->move() && move == tte->move()
&& !excludedMove // Do not allow recursive singular extension search
&& ext < OnePly && ext < OnePly
&& is_lower_bound(tte->type()) && is_lower_bound(tte->type())
&& tte->depth() >= depth - 3 * OnePly) && tte->depth() >= depth - 3 * OnePly)
@ -1131,7 +1259,7 @@ namespace {
if (abs(ttValue) < VALUE_KNOWN_WIN) if (abs(ttValue) < VALUE_KNOWN_WIN)
{ {
Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move); Value excValue = search<false>(pos, ss, ttValue - SingularExtensionMargin - 1, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
if (excValue < ttValue - SingularExtensionMargin) if (excValue < ttValue - SingularExtensionMargin)
ext = OnePly; ext = OnePly;
@ -1144,14 +1272,39 @@ namespace {
movesSearched[moveCount++] = ss[ply].currentMove = move; movesSearched[moveCount++] = ss[ply].currentMove = move;
// Step 12. Futility pruning (is omitted in PV nodes) // Step 12. Futility pruning (is omitted in PV nodes)
if ( !PvNode
&& !isCheck
&& !dangerous
&& !captureOrPromotion
&& !move_is_castle(move)
&& move != ttMove)
{
// Move count based pruning
if ( moveCount >= futility_move_count(depth)
&& ok_to_prune(pos, move, ss[ply].threatMove)
&& bestValue > value_mated_in(PLY_MAX))
continue;
// Value based pruning
Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
+ H.gain(pos.piece_on(move_from(move)), move_to(move));
if (futilityValueScaled < beta)
{
if (futilityValueScaled > bestValue)
bestValue = futilityValueScaled;
continue;
}
}
// Step 13. Make the move // Step 13. Make the move
pos.do_move(move, st, ci, moveIsCheck); pos.do_move(move, st, ci, moveIsCheck);
// Step extra. pv search (only in PV nodes) // Step extra. pv search (only in PV nodes)
// The first move in list is the expected PV // The first move in list is the expected PV
if (moveCount == 1) if (PvNode && moveCount == 1)
value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID); value = -search<true>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
else else
{ {
// Step 14. Reduced search // Step 14. Reduced search
@ -1164,10 +1317,10 @@ namespace {
&& !move_is_castle(move) && !move_is_castle(move)
&& !move_is_killer(move, ss[ply])) && !move_is_killer(move, ss[ply]))
{ {
ss[ply].reduction = pv_reduction(depth, moveCount); ss[ply].reduction = (PvNode ? pv_reduction(depth, moveCount) : nonpv_reduction(depth, moveCount));
if (ss[ply].reduction) if (ss[ply].reduction)
{ {
value = -search(pos, ss, -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID); value = -search<false>(pos, ss, -(alpha+1), -alpha, newDepth-ss[ply].reduction, ply+1, true, threadID);
doFullDepthSearch = (value > alpha); doFullDepthSearch = (value > alpha);
} }
} }
@ -1176,11 +1329,11 @@ namespace {
if (doFullDepthSearch) if (doFullDepthSearch)
{ {
ss[ply].reduction = Depth(0); ss[ply].reduction = Depth(0);
value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID); value = -search<false>(pos, ss, -(alpha+1), -alpha, newDepth, ply+1, true, threadID);
// Step extra. pv search (only in PV nodes) // Step extra. pv search (only in PV nodes)
if (value > alpha && value < beta) if (PvNode && value > alpha && value < beta)
value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID); value = -search<true>(pos, ss, -beta, -alpha, newDepth, ply+1, false, threadID);
} }
} }
@ -1211,342 +1364,7 @@ namespace {
&& !AbortSearch && !AbortSearch
&& !TM.thread_should_stop(threadID) && !TM.thread_should_stop(threadID)
&& TM.split(pos, ss, ply, &alpha, beta, &bestValue, && TM.split(pos, ss, ply, &alpha, beta, &bestValue,
depth, mateThreat, &moveCount, &mp, threadID, true)) depth, mateThreat, &moveCount, &mp, threadID, PvNode))
break;
}
// Step 19. Check for mate and stalemate
// All legal moves have been searched and if there were
// no legal moves, it must be mate or stalemate.
if (moveCount == 0)
return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
// Step 20. Update tables
// If the search is not aborted, update the transposition table,
// history counters, and killer moves.
if (AbortSearch || TM.thread_should_stop(threadID))
return bestValue;
if (bestValue <= oldAlpha)
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
else if (bestValue >= beta)
{
TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
move = ss[ply].pv[ply];
if (!pos.move_is_capture_or_promotion(move))
{
update_history(pos, move, depth, movesSearched, moveCount);
update_killers(move, ss[ply]);
}
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, move);
}
else
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
return bestValue;
}
// search() is the search function for zero-width nodes.
Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
int ply, bool allowNullmove, int threadID, Move excludedMove) {
assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
assert(ply >= 0 && ply < PLY_MAX);
assert(threadID >= 0 && threadID < TM.active_threads());
Move movesSearched[256];
EvalInfo ei;
StateInfo st;
const TTEntry* tte;
Move ttMove, move;
Depth ext, newDepth;
Value bestValue, refinedValue, nullValue, value, futilityValueScaled;
bool isCheck, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
bool mateThreat = false;
int moveCount = 0;
refinedValue = bestValue = value = -VALUE_INFINITE;
if (depth < OnePly)
return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
// Step 1. Initialize node and poll
// Polling can abort search.
init_node(ss, ply, threadID);
// Step 2. Check for aborted search and immediate draw
if (AbortSearch || TM.thread_should_stop(threadID))
return Value(0);
if (pos.is_draw() || ply >= PLY_MAX - 1)
return VALUE_DRAW;
// Step 3. Mate distance pruning
if (value_mated_in(ply) >= beta)
return beta;
if (value_mate_in(ply + 1) < beta)
return beta - 1;
// Step 4. Transposition table lookup
// We don't want the score of a partial search to overwrite a previous full search
// TT value, so we use a different position key in case of an excluded move exists.
Key posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
tte = TT.retrieve(posKey);
ttMove = (tte ? tte->move() : MOVE_NONE);
if (tte && ok_to_use_TT(tte, depth, beta, ply))
{
// Refresh tte entry to avoid aging
TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove);
ss[ply].currentMove = ttMove; // Can be MOVE_NONE
return value_from_tt(tte->value(), ply);
}
// Step 5. Evaluate the position statically
isCheck = pos.is_check();
if (!isCheck)
{
if (tte && (tte->type() & VALUE_TYPE_EVAL))
ss[ply].eval = value_from_tt(tte->value(), ply);
else
ss[ply].eval = evaluate(pos, ei, threadID);
refinedValue = refine_eval(tte, ss[ply].eval, ply); // Enhance accuracy with TT value if possible
update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
}
// Step 6. Razoring
if ( refinedValue < beta - razor_margin(depth)
&& ttMove == MOVE_NONE
&& ss[ply - 1].currentMove != MOVE_NULL
&& depth < RazorDepth
&& !isCheck
&& !value_is_mate(beta)
&& !pos.has_pawn_on_7th(pos.side_to_move()))
{
Value rbeta = beta - razor_margin(depth);
Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
if (v < rbeta)
// Logically we should return (v + razor_margin(depth)), but
// surprisingly this did slightly weaker in tests.
return v;
}
// Step 7. Static null move pruning
// We're betting that the opponent doesn't have a move that will reduce
// the score by more than futility_margin(depth) if we do a null move.
if ( allowNullmove
&& depth < RazorDepth
&& !isCheck
&& !value_is_mate(beta)
&& ok_to_do_nullmove(pos)
&& refinedValue >= beta + futility_margin(depth, 0))
return refinedValue - futility_margin(depth, 0);
// Step 8. Null move search with verification search
// When we jump directly to qsearch() we do a null move only if static value is
// at least beta. Otherwise we do a null move if static value is not more than
// NullMoveMargin under beta.
if ( allowNullmove
&& depth > OnePly
&& !isCheck
&& !value_is_mate(beta)
&& ok_to_do_nullmove(pos)
&& refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0))
{
ss[ply].currentMove = MOVE_NULL;
// Null move dynamic reduction based on depth
int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
// Null move dynamic reduction based on value
if (refinedValue - beta > PawnValueMidgame)
R++;
pos.do_null_move(st);
nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
pos.undo_null_move();
if (nullValue >= beta)
{
// Do not return unproven mate scores
if (nullValue >= value_mate_in(PLY_MAX))
nullValue = beta;
if (depth < 6 * OnePly)
return nullValue;
// Do zugzwang verification search
Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
if (v >= beta)
return nullValue;
} 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;
}
}
// Step 9. Internal iterative deepening
if ( depth >= IIDDepthAtNonPVNodes
&& ttMove == MOVE_NONE
&& !isCheck
&& ss[ply].eval >= beta - IIDMargin)
{
search(pos, ss, beta, depth/2, ply, false, threadID);
ttMove = ss[ply].pv[ply];
tte = TT.retrieve(posKey);
}
// Initialize a MovePicker object for the current position
MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
CheckInfo ci(pos);
// Step 10. Loop through moves
// Loop through all legal moves until no moves remain or a beta cutoff occurs
while ( bestValue < beta
&& (move = mp.get_next_move()) != MOVE_NONE
&& !TM.thread_should_stop(threadID))
{
assert(move_is_ok(move));
if (move == excludedMove)
continue;
moveIsCheck = pos.move_is_check(move, ci);
singleEvasion = (isCheck && mp.number_of_evasions() == 1);
captureOrPromotion = pos.move_is_capture_or_promotion(move);
// Step 11. Decide the new search depth
ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
// Singular extension search. We extend the TT move if its value is much better than
// its siblings. To verify this we do a reduced search on all the other moves but the
// ttMove, if result is lower then ttValue minus a margin then we extend ttMove.
if ( depth >= SingularExtensionDepthAtNonPVNodes
&& tte
&& move == tte->move()
&& !excludedMove // Do not allow recursive singular extension search
&& ext < OnePly
&& is_lower_bound(tte->type())
&& tte->depth() >= depth - 3 * OnePly)
{
Value ttValue = value_from_tt(tte->value(), ply);
if (abs(ttValue) < VALUE_KNOWN_WIN)
{
Value excValue = search(pos, ss, ttValue - SingularExtensionMargin, depth / 2, ply, false, threadID, move);
if (excValue < ttValue - SingularExtensionMargin)
ext = OnePly;
}
}
newDepth = depth - OnePly + ext;
// Update current move (this must be done after singular extension search)
movesSearched[moveCount++] = ss[ply].currentMove = move;
// Step 12. Futility pruning
if ( !isCheck
&& !dangerous
&& !captureOrPromotion
&& !move_is_castle(move)
&& move != ttMove)
{
// Move count based pruning
if ( moveCount >= futility_move_count(depth)
&& ok_to_prune(pos, move, ss[ply].threatMove)
&& bestValue > value_mated_in(PLY_MAX))
continue;
// Value based pruning
Depth predictedDepth = newDepth - nonpv_reduction(depth, moveCount); // We illogically ignore reduction condition depth >= 3*OnePly
futilityValueScaled = ss[ply].eval + futility_margin(predictedDepth, moveCount)
+ H.gain(pos.piece_on(move_from(move)), move_to(move));
if (futilityValueScaled < beta)
{
if (futilityValueScaled > bestValue)
bestValue = futilityValueScaled;
continue;
}
}
// Step 13. Make the move
pos.do_move(move, st, ci, moveIsCheck);
// Step 14. Reduced search, if the move fails high
// will be re-searched at full depth.
bool doFullDepthSearch = true;
if ( depth >= 3*OnePly
&& !dangerous
&& !captureOrPromotion
&& !move_is_castle(move)
&& !move_is_killer(move, ss[ply]))
{
ss[ply].reduction = nonpv_reduction(depth, moveCount);
if (ss[ply].reduction)
{
value = -search(pos, ss, -(beta-1), newDepth-ss[ply].reduction, ply+1, true, threadID);
doFullDepthSearch = (value >= beta);
}
}
// Step 15. Full depth search
if (doFullDepthSearch)
{
ss[ply].reduction = Depth(0);
value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
}
// Step 16. Undo move
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// Step 17. Check for new best move
if (value > bestValue)
{
bestValue = value;
if (value >= beta)
update_pv(ss, ply);
if (value == value_mate_in(ply + 1))
ss[ply].mateKiller = move;
}
// Step 18. Check for split
if ( TM.active_threads() > 1
&& bestValue < beta
&& depth >= MinimumSplitDepth
&& Iteration <= 99
&& TM.available_thread_exists(threadID)
&& !AbortSearch
&& !TM.thread_should_stop(threadID)
&& TM.split(pos, ss, ply, NULL, beta, &bestValue,
depth, mateThreat, &moveCount, &mp, threadID, false))
break; break;
} }
@ -1555,7 +1373,7 @@ namespace {
// no legal moves, it must be mate or stalemate. // no legal moves, it must be mate or stalemate.
// If one move was excluded return fail low score. // If one move was excluded return fail low score.
if (!moveCount) if (!moveCount)
return excludedMove ? beta - 1 : (isCheck ? value_mated_in(ply) : VALUE_DRAW); return excludedMove ? oldAlpha : (isCheck ? value_mated_in(ply) : VALUE_DRAW);
// Step 20. Update tables // Step 20. Update tables
// If the search is not aborted, update the transposition table, // If the search is not aborted, update the transposition table,
@ -1563,9 +1381,10 @@ namespace {
if (AbortSearch || TM.thread_should_stop(threadID)) if (AbortSearch || TM.thread_should_stop(threadID))
return bestValue; return bestValue;
if (bestValue < beta) if (bestValue <= oldAlpha)
TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE); TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
else
else if (bestValue >= beta)
{ {
TM.incrementBetaCounter(pos.side_to_move(), depth, threadID); TM.incrementBetaCounter(pos.side_to_move(), depth, threadID);
move = ss[ply].pv[ply]; move = ss[ply].pv[ply];
@ -1575,8 +1394,9 @@ namespace {
update_history(pos, move, depth, movesSearched, moveCount); update_history(pos, move, depth, movesSearched, moveCount);
update_killers(move, ss[ply]); update_killers(move, ss[ply]);
} }
} }
else
TT.store(posKey, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE); assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
@ -1868,7 +1688,7 @@ namespace {
ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount); ss[sp->ply].reduction = nonpv_reduction(sp->depth, moveCount);
if (ss[sp->ply].reduction) if (ss[sp->ply].reduction)
{ {
value = -search(pos, ss, -(sp->beta-1), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID); value = -search<false>(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID)); doFullDepthSearch = (value >= sp->beta && !TM.thread_should_stop(threadID));
} }
} }
@ -1877,7 +1697,7 @@ namespace {
if (doFullDepthSearch) if (doFullDepthSearch)
{ {
ss[sp->ply].reduction = Depth(0); ss[sp->ply].reduction = Depth(0);
value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID); value = -search<false>(pos, ss, -(sp->alpha+1), -(sp->alpha), newDepth, sp->ply+1, true, threadID);
} }
// Step 16. Undo move // Step 16. Undo move
@ -1974,7 +1794,7 @@ namespace {
if (ss[sp->ply].reduction) if (ss[sp->ply].reduction)
{ {
Value localAlpha = sp->alpha; Value localAlpha = sp->alpha;
value = -search(pos, ss, -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID); value = -search<false>(pos, ss, -(localAlpha+1), -localAlpha, newDepth-ss[sp->ply].reduction, sp->ply+1, true, threadID);
doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID)); doFullDepthSearch = (value > localAlpha && !TM.thread_should_stop(threadID));
} }
} }
@ -1984,7 +1804,7 @@ namespace {
{ {
Value localAlpha = sp->alpha; Value localAlpha = sp->alpha;
ss[sp->ply].reduction = Depth(0); ss[sp->ply].reduction = Depth(0);
value = -search(pos, ss, -localAlpha, newDepth, sp->ply+1, true, threadID); value = -search<false>(pos, ss, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1, true, threadID);
if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID)) if (value > localAlpha && value < sp->beta && !TM.thread_should_stop(threadID))
{ {
@ -1992,7 +1812,7 @@ namespace {
// to be higher or equal then beta, if so, avoid to start a PV search. // to be higher or equal then beta, if so, avoid to start a PV search.
localAlpha = sp->alpha; localAlpha = sp->alpha;
if (localAlpha < sp->beta) if (localAlpha < sp->beta)
value = -search_pv(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, threadID); value = -search<true>(pos, ss, -sp->beta, -localAlpha, newDepth, sp->ply+1, false, threadID);
} }
} }
@ -2032,7 +1852,7 @@ namespace {
// init_node() is called at the beginning of all the search functions // init_node() is called at the beginning of all the search functions
// (search(), search_pv(), qsearch(), and so on) and initializes the // (search() qsearch(), and so on) and initializes the
// search stack object corresponding to the current node. Once every // search stack object corresponding to the current node. Once every
// NodesBetweenPolls nodes, init_node() also calls poll(), which polls // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
// for user input and checks whether it is time to stop the search. // for user input and checks whether it is time to stop the search.
@ -2922,7 +2742,7 @@ namespace {
splitPoint->ply = ply; splitPoint->ply = ply;
splitPoint->depth = depth; splitPoint->depth = depth;
splitPoint->mateThreat = mateThreat; splitPoint->mateThreat = mateThreat;
splitPoint->alpha = pvNode ? *alpha : beta - 1; splitPoint->alpha = *alpha;
splitPoint->beta = beta; splitPoint->beta = beta;
splitPoint->pvNode = pvNode; splitPoint->pvNode = pvNode;
splitPoint->bestValue = *bestValue; splitPoint->bestValue = *bestValue;
@ -2977,12 +2797,10 @@ namespace {
idle_loop(master, splitPoint); idle_loop(master, splitPoint);
// We have returned from the idle loop, which means that all threads are // We have returned from the idle loop, which means that all threads are
// finished. Update alpha, beta and bestValue, and return. // finished. Update alpha and bestValue, and return.
lock_grab(&MPLock); lock_grab(&MPLock);
if (pvNode)
*alpha = splitPoint->alpha; *alpha = splitPoint->alpha;
*bestValue = splitPoint->bestValue; *bestValue = splitPoint->bestValue;
threads[master].activeSplitPoints--; threads[master].activeSplitPoints--;
threads[master].splitPoint = splitPoint->parent; threads[master].splitPoint = splitPoint->parent;