X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=9949e2aeb23477f4cb1eaa511ed89c95c464a04a;hb=243f7b264a81c2981cec2818b47d609d9d3ca119;hp=0e82f04e9959180ecfd97151e0503c6d20b5c861;hpb=8dea070538dcad790de3c5b9720bdbb836a32440;p=stockfish
diff --git a/src/search.cpp b/src/search.cpp
index 0e82f04e..9949e2ae 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -16,25 +16,34 @@
along with this program. If not, see .
*/
+#include "search.h"
+
#include
+#include
+#include
#include
#include
-#include // For std::memset
+#include
+#include
+#include
#include
#include
+#include
+#include
+#include "bitboard.h"
#include "evaluate.h"
#include "misc.h"
#include "movegen.h"
#include "movepick.h"
+#include "nnue/evaluate_nnue.h"
+#include "nnue/nnue_common.h"
#include "position.h"
-#include "search.h"
+#include "syzygy/tbprobe.h"
#include "thread.h"
#include "timeman.h"
#include "tt.h"
#include "uci.h"
-#include "syzygy/tbprobe.h"
-#include "nnue/evaluate_nnue.h"
namespace Stockfish {
@@ -63,16 +72,17 @@ namespace {
enum NodeType { NonPV, PV, Root };
// Futility margin
- Value futility_margin(Depth d, bool improving) {
- return Value(140 * (d - improving));
+ Value futility_margin(Depth d, bool noTtCutNode, bool improving) {
+ return Value((140 - 40 * noTtCutNode) * (d - improving));
}
- // Reductions lookup table, initialized at startup
+ // Reductions lookup table initialized at startup
int Reductions[MAX_MOVES]; // [depth or moveNumber]
Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) {
- int r = Reductions[d] * Reductions[mn];
- return (r + 1372 - int(delta) * 1073 / int(rootDelta)) / 1024 + (!i && r > 936);
+ int reductionScale = Reductions[d] * Reductions[mn];
+ return (reductionScale + 1372 - int(delta) * 1073 / int(rootDelta)) / 1024
+ + (!i && reductionScale > 936);
}
constexpr int futility_move_count(bool improving, Depth depth) {
@@ -90,10 +100,12 @@ namespace {
return VALUE_DRAW - 1 + Value(thisThread->nodes & 0x2);
}
- // Skill structure is used to implement strength limit. If we have an uci_elo then
- // we convert it to a suitable fractional skill level using anchoring to CCRL Elo
- // (goldfish 1.13 = 2000) and a fit through Ordo derived Elo for match (TC 60+0.6)
- // results spanning a wide range of k values.
+ // Skill structure is used to implement strength limit.
+ // If we have a UCI_Elo, we convert it to an appropriate skill level, anchored to the Stash engine.
+ // This method is based on a fit of the Elo results for games played between the master at various
+ // skill levels and various versions of the Stash engine, all ranked at CCRL.
+ // Skill 0 .. 19 now covers CCRL Blitz Elo from 1320 to 3190, approximately
+ // Reference: https://github.com/vondele/Stockfish/commit/a08b8d4e9711c20acedbfe17d618c3c384b339ec
struct Skill {
Skill(int skill_level, int uci_elo) {
if (uci_elo)
@@ -262,10 +274,9 @@ void MainThread::search() {
void Thread::search() {
- // To allow access to (ss-7) up to (ss+2), the stack must be oversized.
- // The former is needed to allow update_continuation_histories(ss-1, ...),
- // which accesses its argument at ss-6, also near the root.
- // The latter is needed for statScore and killer initialization.
+ // Allocate stack with extra size to allow access from (ss-7) to (ss+2)
+ // (ss-7) is needed for update_continuation_histories(ss-1, ...) which accesses (ss-6)
+ // (ss+2) is needed for initialization of statScore and killers
Stack stack[MAX_PLY+10], *ss = stack+7;
Move pv[MAX_PLY+1];
Value alpha, beta, delta;
@@ -304,9 +315,9 @@ void Thread::search() {
Skill skill(Options["Skill Level"], Options["UCI_LimitStrength"] ? int(Options["UCI_Elo"]) : 0);
// When playing with strength handicap enable MultiPV search that we will
- // use behind the scenes to retrieve a set of possible moves.
+ // use behind-the-scenes to retrieve a set of possible moves.
if (skill.enabled())
- multiPV = std::max(multiPV, (size_t)4);
+ multiPV = std::max(multiPV, size_t(4));
multiPV = std::min(multiPV, rootMoves.size());
@@ -321,7 +332,7 @@ void Thread::search() {
if (mainThread)
totBestMoveChanges /= 2;
- // Save the last iteration's scores before first PV line is searched and
+ // Save the last iteration's scores before the first PV line is searched and
// all the move scores except the (new) PV are set to -VALUE_INFINITE.
for (RootMove& rm : rootMoves)
rm.previousScore = rm.score;
@@ -352,7 +363,7 @@ void Thread::search() {
alpha = std::max(prev - delta,-VALUE_INFINITE);
beta = std::min(prev + delta, VALUE_INFINITE);
- // Adjust optimism based on root move's previousScore
+ // Adjust optimism based on root move's previousScore (~4 Elo)
int opt = 109 * prev / (std::abs(prev) + 141);
optimism[ us] = Value(opt);
optimism[~us] = -optimism[us];
@@ -363,16 +374,16 @@ void Thread::search() {
int failedHighCnt = 0;
while (true)
{
- // Adjust the effective depth searched, but ensuring at least one effective increment for every
+ // Adjust the effective depth searched, but ensure at least one effective increment for every
// four searchAgain steps (see issue #2717).
Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - 3 * (searchAgainCounter + 1) / 4);
bestValue = Stockfish::search(rootPos, ss, alpha, beta, adjustedDepth, false);
// Bring the best move to the front. It is critical that sorting
// is done with a stable algorithm because all the values but the
- // first and eventually the new best one are set to -VALUE_INFINITE
+ // first and eventually the new best one is set to -VALUE_INFINITE
// and we want to keep the same order for all the moves except the
- // new PV that goes to the front. Note that in case of MultiPV
+ // new PV that goes to the front. Note that in the case of MultiPV
// search the already searched PV lines are preserved.
std::stable_sort(rootMoves.begin() + pvIdx, rootMoves.begin() + pvLast);
@@ -440,7 +451,7 @@ void Thread::search() {
if (!mainThread)
continue;
- // If skill level is enabled and time is up, pick a sub-optimal best move
+ // If the skill level is enabled and time is up, pick a sub-optimal best move
if (skill.enabled() && skill.time_to_pick(rootDepth))
skill.pick_best(multiPV);
@@ -498,7 +509,7 @@ void Thread::search() {
mainThread->previousTimeReduction = timeReduction;
- // If skill level is enabled, swap best PV line with the sub-optimal one
+ // If the skill level is enabled, swap the best PV line with the sub-optimal one
if (skill.enabled())
std::swap(rootMoves[0], *std::find(rootMoves.begin(), rootMoves.end(),
skill.best ? skill.best : skill.pick_best(multiPV)));
@@ -515,10 +526,13 @@ namespace {
constexpr bool PvNode = nodeType != NonPV;
constexpr bool rootNode = nodeType == Root;
- // Check if we have an upcoming move which draws by repetition, or
+ // Dive into quiescence search when the depth reaches zero
+ if (depth <= 0)
+ return qsearch(pos, ss, alpha, beta);
+
+ // Check if we have an upcoming move that draws by repetition, or
// if the opponent had an alternative move earlier to this position.
if ( !rootNode
- && pos.rule50_count() >= 3
&& alpha < VALUE_DRAW
&& pos.has_game_cycle(ss->ply))
{
@@ -527,10 +541,6 @@ namespace {
return alpha;
}
- // Dive into quiescence search when the depth reaches zero
- if (depth <= 0)
- return qsearch(pos, ss, alpha, beta);
-
assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
assert(0 < depth && depth < MAX_PLY);
@@ -548,7 +558,7 @@ namespace {
bool givesCheck, improving, priorCapture, singularQuietLMR;
bool capture, moveCountPruning, ttCapture;
Piece movedPiece;
- int moveCount, captureCount, quietCount, improvement;
+ int moveCount, captureCount, quietCount;
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
@@ -580,8 +590,8 @@ namespace {
// would be at best mate_in(ss->ply+1), but if alpha is already bigger because
// a shorter mate was found upward in the tree then there is no need to search
// because we will never beat the current alpha. Same logic but with reversed
- // signs applies also in the opposite condition of being mated instead of giving
- // mate. In this case return a fail-high score.
+ // signs apply also in the opposite condition of being mated instead of giving
+ // mate. In this case, return a fail-high score.
alpha = std::max(mated_in(ss->ply), alpha);
beta = std::min(mate_in(ss->ply+1), beta);
if (alpha >= beta)
@@ -616,7 +626,7 @@ namespace {
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
&& !excludedMove
- && tte->depth() > depth - (tte->bound() == BOUND_EXACT)
+ && tte->depth() > depth
&& ttValue != VALUE_NONE // Possible in case of TT access race or if !ttHit
&& (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER)))
{
@@ -708,12 +718,11 @@ namespace {
// Skip early pruning when in check
ss->staticEval = eval = VALUE_NONE;
improving = false;
- improvement = 0;
goto moves_loop;
}
else if (excludedMove)
{
- // Providing the hint that this node's accumulator will be used often brings significant Elo gain (13 Elo)
+ // Providing the hint that this node's accumulator will be used often brings significant Elo gain (~13 Elo)
Eval::NNUE::hint_common_parent_position(pos);
eval = ss->staticEval;
}
@@ -734,7 +743,7 @@ namespace {
else
{
ss->staticEval = eval = evaluate(pos);
- // Save static evaluation into transposition table
+ // Save static evaluation into the transposition table
tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
}
@@ -745,16 +754,16 @@ namespace {
thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus;
}
- // Set up the improvement variable, which is the difference between the current
- // static evaluation and the previous static evaluation at our turn (if we were
- // in check at our previous move we look at the move prior to it). The improvement
- // margin and the improving flag are used in various pruning heuristics.
- improvement = (ss-2)->staticEval != VALUE_NONE ? ss->staticEval - (ss-2)->staticEval
- : (ss-4)->staticEval != VALUE_NONE ? ss->staticEval - (ss-4)->staticEval
- : 173;
- improving = improvement > 0;
+ // Set up the improving flag, which is true if current static evaluation is
+ // bigger than the previous static evaluation at our turn (if we were in
+ // check at our previous move we look at static evaluation at move prior to it
+ // and if we were in check at move prior to it flag is set to true) and is
+ // false otherwise. The improving flag is used in various pruning heuristics.
+ improving = (ss-2)->staticEval != VALUE_NONE ? ss->staticEval > (ss-2)->staticEval
+ : (ss-4)->staticEval != VALUE_NONE ? ss->staticEval > (ss-4)->staticEval
+ : true;
- // Step 7. Razoring (~1 Elo).
+ // Step 7. Razoring (~1 Elo)
// If eval is really low check with qsearch if it can exceed alpha, if it can't,
// return a fail low.
if (eval < alpha - 456 - 252 * depth * depth)
@@ -764,13 +773,13 @@ namespace {
return value;
}
- // Step 8. Futility pruning: child node (~40 Elo).
+ // Step 8. Futility pruning: child node (~40 Elo)
// The depth condition is important for mate finding.
if ( !ss->ttPv
&& depth < 9
- && eval - futility_margin(depth, improving) - (ss-1)->statScore / 306 >= beta
+ && eval - futility_margin(depth, cutNode && !ss->ttHit, improving) - (ss-1)->statScore / 306 >= beta
&& eval >= beta
- && eval < 24923) // larger than VALUE_KNOWN_WIN, but smaller than TB wins
+ && eval < 24923) // smaller than TB wins
return eval;
// Step 9. Null move search with verification search (~35 Elo)
@@ -779,10 +788,11 @@ namespace {
&& (ss-1)->statScore < 17329
&& eval >= beta
&& eval >= ss->staticEval
- && ss->staticEval >= beta - 21 * depth - improvement * 99 / 1300 + 258
+ && ss->staticEval >= beta - 21 * depth + 258
&& !excludedMove
&& pos.non_pawn_material(us)
- && (ss->ply >= thisThread->nmpMinPly))
+ && ss->ply >= thisThread->nmpMinPly
+ && beta > VALUE_TB_LOSS_IN_MAX_PLY)
{
assert(eval - beta >= 0);
@@ -801,10 +811,9 @@ namespace {
if (nullValue >= beta)
{
// Do not return unproven mate or TB scores
- if (nullValue >= VALUE_TB_WIN_IN_MAX_PLY)
- nullValue = beta;
+ nullValue = std::min(nullValue, VALUE_TB_WIN_IN_MAX_PLY-1);
- if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 14))
+ if (thisThread->nmpMinPly || depth < 14)
return nullValue;
assert(!thisThread->nmpMinPly); // Recursive verification is not allowed
@@ -822,7 +831,7 @@ namespace {
}
}
- // Step 10. If the position doesn't a have ttMove, decrease depth by 2
+ // Step 10. If the position doesn't have a ttMove, decrease depth by 2
// (or by 4 if the TT entry for the current position was hit and the stored depth is greater than or equal to the current depth).
// Use qsearch if depth is equal or below zero (~9 Elo)
if ( PvNode
@@ -845,10 +854,10 @@ namespace {
if ( !PvNode
&& depth > 3
&& abs(beta) < VALUE_TB_WIN_IN_MAX_PLY
- // if value from transposition table is lower than probCutBeta, don't attempt probCut
+ // If value from transposition table is lower than probCutBeta, don't attempt probCut
// there and in further interactions with transposition table cutoff depth is set to depth - 3
// because probCut search has depth set to depth - 4 but we also do a move before it
- // so effective depth is equal to depth - 3
+ // So effective depth is equal to depth - 3
&& !( tte->depth() >= depth - 3
&& ttValue != VALUE_NONE
&& ttValue < probCutBeta))
@@ -900,8 +909,8 @@ moves_loop: // When in check, search starts here
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 4
&& ttValue >= probCutBeta
- && abs(ttValue) <= VALUE_KNOWN_WIN
- && abs(beta) <= VALUE_KNOWN_WIN)
+ && abs(ttValue) < VALUE_TB_WIN_IN_MAX_PLY
+ && abs(beta) < VALUE_TB_WIN_IN_MAX_PLY)
return probCutBeta;
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
@@ -920,7 +929,8 @@ moves_loop: // When in check, search starts here
moveCountPruning = singularQuietLMR = false;
// Indicate PvNodes that will probably fail low if the node was searched
- // at a depth equal or greater than the current depth, and the result of this search was a fail low.
+ // at a depth equal to or greater than the current depth, and the result
+ // of this search was a fail low.
bool likelyFailLow = PvNode
&& ttMove
&& (tte->bound() & BOUND_UPPER)
@@ -936,8 +946,8 @@ moves_loop: // When in check, search starts here
continue;
// At root obey the "searchmoves" option and skip moves not listed in Root
- // Move List. As a consequence any illegal move is also skipped. In MultiPV
- // mode we also skip PV moves which have been already searched and those
+ // Move List. As a consequence, any illegal move is also skipped. In MultiPV
+ // mode we also skip PV moves that have been already searched and those
// of lower "TB rank" if we are in a TB root position.
if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->pvIdx,
thisThread->rootMoves.begin() + thisThread->pvLast, move))
@@ -986,13 +996,13 @@ moves_loop: // When in check, search starts here
if ( !givesCheck
&& lmrDepth < 7
&& !ss->inCheck
- && ss->staticEval + 197 + 248 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))]
+ && ss->staticEval + 197 + 248 * lmrDepth + PieceValue[pos.piece_on(to_sq(move))]
+ captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 7 < alpha)
continue;
- // SEE based pruning (~11 Elo)
+ // SEE based pruning for captures and checks (~11 Elo)
if (!pos.see_ge(move, Value(-205) * depth))
- continue;
+ continue;
}
else
{
@@ -1019,7 +1029,7 @@ moves_loop: // When in check, search starts here
lmrDepth = std::max(lmrDepth, 0);
// Prune moves with negative SEE (~4 Elo)
- if (!pos.see_ge(move, Value(-27 * lmrDepth * lmrDepth - 16 * lmrDepth)))
+ if (!pos.see_ge(move, Value(-31 * lmrDepth * lmrDepth)))
continue;
}
}
@@ -1031,14 +1041,17 @@ moves_loop: // When in check, search starts here
// Singular extension search (~94 Elo). If all moves but one fail low on a
// search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
// then that move is singular and should be extended. To verify this we do
- // a reduced search on all the other moves but the ttMove and if the
- // result is lower than ttValue minus a margin, then we will extend the ttMove.
+ // a reduced search on all the other moves but the ttMove and if the result
+ // is lower than ttValue minus a margin, then we will extend the ttMove. Note
+ // that depth margin and singularBeta margin are known for having non-linear
+ // scaling. Their values are optimized to time controls of 180+1.8 and longer
+ // so changing them requires tests at this type of time controls.
if ( !rootNode
&& depth >= 4 - (thisThread->completedDepth > 22) + 2 * (PvNode && tte->is_pv())
&& move == ttMove
&& !excludedMove // Avoid recursive singular search
/* && ttValue != VALUE_NONE Already implicit in the next condition */
- && abs(ttValue) < VALUE_KNOWN_WIN
+ && abs(ttValue) < VALUE_TB_WIN_IN_MAX_PLY
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3)
{
@@ -1065,10 +1078,10 @@ moves_loop: // When in check, search starts here
}
// Multi-cut pruning
- // Our ttMove is assumed to fail high, and now we failed high also on a reduced
- // search without the ttMove. So we assume this expected Cut-node is not singular,
- // that multiple moves fail high, and we can prune the whole subtree by returning
- // a soft bound.
+ // Our ttMove is assumed to fail high, and now we failed high also on a
+ // reduced search without the ttMove. So we assume this expected cut-node
+ // is not singular, that multiple moves fail high, and we can prune the
+ // whole subtree by returning a softbound.
else if (singularBeta >= beta)
return singularBeta;
@@ -1076,13 +1089,13 @@ moves_loop: // When in check, search starts here
else if (ttValue >= beta)
extension = -2 - !PvNode;
+ // If we are on a cutNode, reduce it based on depth (negative extension) (~1 Elo)
+ else if (cutNode)
+ extension = depth < 17 ? -3 : -1;
+
// If the eval of ttMove is less than value, we reduce it (negative extension) (~1 Elo)
else if (ttValue <= value)
extension = -1;
-
- // If the eval of ttMove is less than alpha, we reduce it (negative extension) (~1 Elo)
- else if (ttValue <= alpha)
- extension = -1;
}
// Check extensions (~1 Elo)
@@ -1115,12 +1128,11 @@ moves_loop: // When in check, search starts here
// Step 16. Make the move
pos.do_move(move, st, givesCheck);
- // Decrease reduction if position is or has been on the PV
- // and node is not likely to fail low. (~3 Elo)
+ // Decrease reduction if position is or has been on the PV and not likely to fail low. (~3 Elo)
// Decrease further on cutNodes. (~1 Elo)
if ( ss->ttPv
&& !likelyFailLow)
- r -= cutNode && tte->depth() >= depth + 3 ? 3 : 2;
+ r -= cutNode && tte->depth() >= depth ? 3 : 2;
// Decrease reduction if opponent's move count is high (~1 Elo)
if ((ss-1)->moveCount > 8)
@@ -1134,18 +1146,24 @@ moves_loop: // When in check, search starts here
if (ttCapture)
r++;
- // Decrease reduction for PvNodes based on depth (~2 Elo)
+ // Decrease reduction for PvNodes (~2 Elo)
if (PvNode)
- r -= 1 + 12 / (3 + depth);
+ r--;
// Decrease reduction if ttMove has been singularly extended (~1 Elo)
if (singularQuietLMR)
r--;
+ // Increase reduction on repetition (~1 Elo)
+ if ( move == (ss-4)->currentMove
+ && pos.has_repeated())
+ r += 2;
+
// Increase reduction if next ply has a lot of fail high (~5 Elo)
if ((ss+1)->cutoffCnt > 3)
r++;
+ // Decrease reduction for first generated move (ttMove)
else if (move == ttMove)
r--;
@@ -1160,7 +1178,7 @@ moves_loop: // When in check, search starts here
// Step 17. Late moves reduction / extension (LMR, ~117 Elo)
// We use various heuristics for the sons of a node after the first son has
- // been searched. In general we would like to reduce them, but there are many
+ // been searched. In general, we would like to reduce them, but there are many
// cases where we extend a son if it has good chances to be "interesting".
if ( depth >= 2
&& moveCount > 1 + (PvNode && ss->ply <= 1)
@@ -1175,10 +1193,10 @@ moves_loop: // When in check, search starts here
value = -search(pos, ss+1, -(alpha+1), -alpha, d, true);
- // Do full depth search when reduced LMR search fails high
+ // Do a full-depth search when reduced LMR search fails high
if (value > alpha && d < newDepth)
{
- // Adjust full depth search based on LMR results - if result
+ // Adjust full-depth search based on LMR results - if the result
// was good enough search deeper, if it was bad enough search shallower
const bool doDeeperSearch = value > (bestValue + 64 + 11 * (newDepth - d));
const bool doEvenDeeperSearch = value > alpha + 711 && ss->doubleExtensions <= 6;
@@ -1199,7 +1217,7 @@ moves_loop: // When in check, search starts here
}
}
- // Step 18. Full depth search when LMR is skipped. If expected reduction is high, reduce its depth by 1.
+ // Step 18. Full-depth search when LMR is skipped. If expected reduction is high, reduce its depth by 1.
else if (!PvNode || moveCount > 1)
{
// Increase reduction for cut nodes and not ttMove (~1 Elo)
@@ -1209,10 +1227,9 @@ moves_loop: // When in check, search starts here
value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth - (r > 3), !cutNode);
}
- // For PV nodes only, do a full PV search on the first move or after a fail
- // high (in the latter case search only if value < beta), otherwise let the
- // parent node fail low with value <= alpha and try another move.
- if (PvNode && (moveCount == 1 || (value > alpha && (rootNode || value < beta))))
+ // For PV nodes only, do a full PV search on the first move or after a fail high,
+ // otherwise let the parent node fail low with value <= alpha and try another move.
+ if (PvNode && (moveCount == 1 || value > alpha))
{
(ss+1)->pv = pv;
(ss+1)->pv[0] = MOVE_NONE;
@@ -1272,7 +1289,7 @@ moves_loop: // When in check, search starts here
++thisThread->bestMoveChanges;
}
else
- // All other moves but the PV are set to the lowest value: this
+ // All other moves but the PV, are set to the lowest value: this
// is not a problem when sorting because the sort is stable and the
// move position in the list is preserved - just the PV is pushed up.
rm.score = -VALUE_INFINITE;
@@ -1297,12 +1314,12 @@ moves_loop: // When in check, search starts here
}
else
{
- // Reduce other moves if we have found at least one score improvement (~1 Elo)
- // Reduce more for depth > 3 and depth < 12 (~1 Elo)
- if ( depth > 1
+ // Reduce other moves if we have found at least one score improvement (~2 Elo)
+ if ( depth > 2
+ && depth < 12
&& beta < 14362
&& value > -12393)
- depth -= depth > 3 && depth < 12 ? 2 : 1;
+ depth -= 2;
assert(depth > 0);
alpha = value; // Update alpha! Always alpha < beta
@@ -1311,7 +1328,7 @@ moves_loop: // When in check, search starts here
}
- // If the move is worse than some previously searched move, remember it to update its stats later
+ // If the move is worse than some previously searched move, remember it, to update its stats later
if (move != bestMove)
{
if (capture && captureCount < 32)
@@ -1323,7 +1340,7 @@ moves_loop: // When in check, search starts here
}
// The following condition would detect a stop only after move loop has been
- // completed. But in this case bestValue is valid because we have fully
+ // completed. But in this case, bestValue is valid because we have fully
// searched our subtree, and we can anyhow save the result in TT.
/*
if (Threads.stop)
@@ -1342,7 +1359,7 @@ moves_loop: // When in check, search starts here
ss->inCheck ? mated_in(ss->ply)
: VALUE_DRAW;
- // If there is a move which produces search value greater than alpha we update stats of searched moves
+ // If there is a move that produces search value greater than alpha we update the stats of searched moves
else if (bestMove)
update_all_stats(pos, ss, bestMove, bestValue, beta, prevSq,
quietsSearched, quietCount, capturesSearched, captureCount, depth);
@@ -1350,8 +1367,9 @@ moves_loop: // When in check, search starts here
// Bonus for prior countermove that caused the fail low
else if (!priorCapture && prevSq != SQ_NONE)
{
- int bonus = (depth > 5) + (PvNode || cutNode) + (bestValue < alpha - 113 * depth) + ((ss-1)->moveCount > 12);
+ int bonus = (depth > 5) + (PvNode || cutNode) + (bestValue < alpha - 800) + ((ss-1)->moveCount > 12);
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * bonus);
+ thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << stat_bonus(depth) * bonus / 2;
}
if (PvNode)
@@ -1388,6 +1406,16 @@ moves_loop: // When in check, search starts here
assert(PvNode || (alpha == beta - 1));
assert(depth <= 0);
+ // Check if we have an upcoming move that draws by repetition, or
+ // if the opponent had an alternative move earlier to this position.
+ if ( alpha < VALUE_DRAW
+ && pos.has_game_cycle(ss->ply))
+ {
+ alpha = value_draw(pos.this_thread());
+ if (alpha >= beta)
+ return alpha;
+ }
+
Move pv[MAX_PLY+1];
StateInfo st;
ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
@@ -1441,10 +1469,7 @@ moves_loop: // When in check, search starts here
// Step 4. Static evaluation of the position
if (ss->inCheck)
- {
- ss->staticEval = VALUE_NONE;
bestValue = futilityBase = -VALUE_INFINITE;
- }
else
{
if (ss->ttHit)
@@ -1460,9 +1485,8 @@ moves_loop: // When in check, search starts here
}
else
// In case of null move search use previous static eval with a different sign
- ss->staticEval = bestValue =
- (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
- : -(ss-1)->staticEval;
+ ss->staticEval = bestValue = (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
+ : -(ss-1)->staticEval;
// Stand pat. Return immediately if static value is at least beta
if (bestValue >= beta)
@@ -1475,10 +1499,10 @@ moves_loop: // When in check, search starts here
return bestValue;
}
- if (PvNode && bestValue > alpha)
+ if (bestValue > alpha)
alpha = bestValue;
- futilityBase = bestValue + 200;
+ futilityBase = std::min(ss->staticEval, bestValue) + 200;
}
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
@@ -1489,7 +1513,7 @@ moves_loop: // When in check, search starts here
// to search the moves. Because the depth is <= 0 here, only captures,
// queen promotions, and other checks (only if depth >= DEPTH_QS_CHECKS)
// will be generated.
- Square prevSq = (ss-1)->currentMove != MOVE_NULL ? to_sq((ss-1)->currentMove) : SQ_NONE;
+ Square prevSq = is_ok((ss-1)->currentMove) ? to_sq((ss-1)->currentMove) : SQ_NONE;
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
&thisThread->captureHistory,
contHist,
@@ -1501,97 +1525,110 @@ moves_loop: // When in check, search starts here
// or a beta cutoff occurs.
while ((move = mp.next_move()) != MOVE_NONE)
{
- assert(is_ok(move));
-
- // Check for legality
- if (!pos.legal(move))
- continue;
+ assert(is_ok(move));
- givesCheck = pos.gives_check(move);
- capture = pos.capture_stage(move);
+ // Check for legality
+ if (!pos.legal(move))
+ continue;
- moveCount++;
+ givesCheck = pos.gives_check(move);
+ capture = pos.capture_stage(move);
- // Step 6. Pruning.
- if (bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
- {
- // Futility pruning and moveCount pruning (~10 Elo)
- if ( !givesCheck
- && to_sq(move) != prevSq
- && futilityBase > -VALUE_KNOWN_WIN
- && type_of(move) != PROMOTION)
- {
- if (moveCount > 2)
- continue;
+ moveCount++;
- futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
+ // Step 6. Pruning.
+ if (bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
+ {
+ // Futility pruning and moveCount pruning (~10 Elo)
+ if ( !givesCheck
+ && to_sq(move) != prevSq
+ && futilityBase > VALUE_TB_LOSS_IN_MAX_PLY
+ && type_of(move) != PROMOTION)
+ {
+ if (moveCount > 2)
+ continue;
- if (futilityValue <= alpha)
- {
- bestValue = std::max(bestValue, futilityValue);
- continue;
- }
+ futilityValue = futilityBase + PieceValue[pos.piece_on(to_sq(move))];
- if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
- {
- bestValue = std::max(bestValue, futilityBase);
- continue;
- }
- }
+ // If static eval + value of piece we are going to capture is much lower
+ // than alpha we can prune this move
+ if (futilityValue <= alpha)
+ {
+ bestValue = std::max(bestValue, futilityValue);
+ continue;
+ }
- // We prune after 2nd quiet check evasion where being 'in check' is implicitly checked through the counter
- // and being a 'quiet' apart from being a tt move is assumed after an increment because captures are pushed ahead.
- if (quietCheckEvasions > 1)
- break;
+ // If static eval is much lower than alpha and move is not winning material
+ // we can prune this move
+ if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
+ {
+ bestValue = std::max(bestValue, futilityBase);
+ continue;
+ }
- // Continuation history based pruning (~3 Elo)
- if ( !capture
- && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < 0
- && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < 0)
- continue;
+ // If static exchange evaluation is much worse than what is needed to not
+ // fall below alpha we can prune this move
+ if (futilityBase > alpha && !pos.see_ge(move, (alpha - futilityBase) * 4))
+ {
+ bestValue = alpha;
+ continue;
+ }
+ }
- // Do not search moves with bad enough SEE values (~5 Elo)
- if (!pos.see_ge(move, Value(-95)))
- continue;
- }
+ // We prune after the second quiet check evasion move, where being 'in check' is
+ // implicitly checked through the counter, and being a 'quiet move' apart from
+ // being a tt move is assumed after an increment because captures are pushed ahead.
+ if (quietCheckEvasions > 1)
+ break;
+
+ // Continuation history based pruning (~3 Elo)
+ if ( !capture
+ && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < 0
+ && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < 0)
+ continue;
+
+ // Do not search moves with bad enough SEE values (~5 Elo)
+ if (!pos.see_ge(move, Value(-95)))
+ continue;
+ }
- // Speculative prefetch as early as possible
- prefetch(TT.first_entry(pos.key_after(move)));
+ // Speculative prefetch as early as possible
+ prefetch(TT.first_entry(pos.key_after(move)));
- // Update the current move
- ss->currentMove = move;
- ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
- [capture]
- [pos.moved_piece(move)]
- [to_sq(move)];
+ // Update the current move
+ ss->currentMove = move;
+ ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
+ [capture]
+ [pos.moved_piece(move)]
+ [to_sq(move)];
- quietCheckEvasions += !capture && ss->inCheck;
+ quietCheckEvasions += !capture && ss->inCheck;
- // Step 7. Make and search the move
- pos.do_move(move, st, givesCheck);
- value = -qsearch(pos, ss+1, -beta, -alpha, depth - 1);
- pos.undo_move(move);
+ // Step 7. Make and search the move
+ pos.do_move(move, st, givesCheck);
+ value = -qsearch(pos, ss+1, -beta, -alpha, depth - 1);
+ pos.undo_move(move);
- assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
+ assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
- // Step 8. Check for a new best move
- if (value > bestValue)
- {
- bestValue = value;
+ // Step 8. Check for a new best move
+ if (value > bestValue)
+ {
+ bestValue = value;
- if (value > alpha)
- {
- bestMove = move;
+ if (value > alpha)
+ {
+ bestMove = move;
- if (PvNode) // Update pv even in fail-high case
- update_pv(ss->pv, move, (ss+1)->pv);
+ if (PvNode) // Update pv even in fail-high case
+ update_pv(ss->pv, move, (ss+1)->pv);
- if (PvNode && value < beta) // Update alpha here!
- alpha = value;
- else
- break; // Fail high
- }
- }
+ if (value < beta) // Update alpha here!
+ alpha = value;
+ else
+ break; // Fail high
+ }
+ }
}
// Step 9. Check for mate
@@ -1680,28 +1717,28 @@ moves_loop: // When in check, search starts here
Piece moved_piece = pos.moved_piece(bestMove);
PieceType captured;
- int bonus1 = stat_bonus(depth + 1);
+ int quietMoveBonus = stat_bonus(depth + 1);
if (!pos.capture_stage(bestMove))
{
- int bonus2 = bestValue > beta + 145 ? bonus1 // larger bonus
- : stat_bonus(depth); // smaller bonus
+ int bestMoveBonus = bestValue > beta + 145 ? quietMoveBonus // larger bonus
+ : stat_bonus(depth); // smaller bonus
// Increase stats for the best move in case it was a quiet move
- update_quiet_stats(pos, ss, bestMove, bonus2);
+ update_quiet_stats(pos, ss, bestMove, bestMoveBonus);
// Decrease stats for all non-best quiet moves
for (int i = 0; i < quietCount; ++i)
{
- thisThread->mainHistory[us][from_to(quietsSearched[i])] << -bonus2;
- update_continuation_histories(ss, pos.moved_piece(quietsSearched[i]), to_sq(quietsSearched[i]), -bonus2);
+ thisThread->mainHistory[us][from_to(quietsSearched[i])] << -bestMoveBonus;
+ update_continuation_histories(ss, pos.moved_piece(quietsSearched[i]), to_sq(quietsSearched[i]), -bestMoveBonus);
}
}
else
{
// Increase stats for the best move in case it was a capture move
captured = type_of(pos.piece_on(to_sq(bestMove)));
- captureHistory[moved_piece][to_sq(bestMove)][captured] << bonus1;
+ captureHistory[moved_piece][to_sq(bestMove)][captured] << quietMoveBonus;
}
// Extra penalty for a quiet early move that was not a TT move or
@@ -1709,14 +1746,14 @@ moves_loop: // When in check, search starts here
if ( prevSq != SQ_NONE
&& ((ss-1)->moveCount == 1 + (ss-1)->ttHit || ((ss-1)->currentMove == (ss-1)->killers[0]))
&& !pos.captured_piece())
- update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -bonus1);
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -quietMoveBonus);
// Decrease stats for all non-best capture moves
for (int i = 0; i < captureCount; ++i)
{
moved_piece = pos.moved_piece(capturesSearched[i]);
captured = type_of(pos.piece_on(to_sq(capturesSearched[i])));
- captureHistory[moved_piece][to_sq(capturesSearched[i])][captured] << -bonus1;
+ captureHistory[moved_piece][to_sq(capturesSearched[i])][captured] << -quietMoveBonus;
}
}
@@ -1728,7 +1765,7 @@ moves_loop: // When in check, search starts here
for (int i : {1, 2, 4, 6})
{
- // Only update first 2 continuation histories if we are in check
+ // Only update the first 2 continuation histories if we are in check
if (ss->inCheck && i > 2)
break;
if (is_ok((ss-i)->currentMove))
@@ -1761,7 +1798,7 @@ moves_loop: // When in check, search starts here
}
}
- // When playing with strength handicap, choose best move among a set of RootMoves
+ // When playing with strength handicap, choose the best move among a set of RootMoves
// using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
Move Skill::pick_best(size_t multiPV) {
@@ -1771,7 +1808,7 @@ moves_loop: // When in check, search starts here
// RootMoves are already sorted by score in descending order
Value topScore = rootMoves[0].score;
- int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
+ int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValue);
int maxScore = -VALUE_INFINITE;
double weakness = 120 - 2 * level;
@@ -1806,7 +1843,7 @@ void MainThread::check_time() {
return;
// When using nodes, ensure checking rate is not lower than 0.1% of nodes
- callsCnt = Limits.nodes ? std::min(1024, int(Limits.nodes / 1024)) : 1024;
+ callsCnt = Limits.nodes ? std::min(512, int(Limits.nodes / 1024)) : 512;
static TimePoint lastInfoTime = now();
@@ -1823,9 +1860,9 @@ void MainThread::check_time() {
if (ponder)
return;
- if ( (Limits.use_time_management() && (elapsed > Time.maximum() - 10 || stopOnPonderhit))
+ if ( (Limits.use_time_management() && (elapsed > Time.maximum() || stopOnPonderhit))
|| (Limits.movetime && elapsed >= Limits.movetime)
- || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
+ || (Limits.nodes && Threads.nodes_searched() >= uint64_t(Limits.nodes)))
Threads.stop = true;
}
@@ -1839,7 +1876,7 @@ string UCI::pv(const Position& pos, Depth depth) {
TimePoint elapsed = Time.elapsed() + 1;
const RootMoves& rootMoves = pos.this_thread()->rootMoves;
size_t pvIdx = pos.this_thread()->pvIdx;
- size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
+ size_t multiPV = std::min(size_t(Options["MultiPV"]), rootMoves.size());
uint64_t nodesSearched = Threads.nodes_searched();
uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0);
@@ -1892,7 +1929,7 @@ string UCI::pv(const Position& pos, Depth depth) {
/// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
/// before exiting the search, for instance, in case we stop the search during a
/// fail high at root. We try hard to have a ponder move to return to the GUI,
-/// otherwise in case of 'ponder on' we have nothing to think on.
+/// otherwise in case of 'ponder on' we have nothing to think about.
bool RootMove::extract_ponder_from_tt(Position& pos) {