Tuned values for search constants

Tuned search constants after many search patches since the last
successful tune.

1st LTC @ 60+0.6 th 1 :
LLR: 2.97 (-2.94,2.94) {0.25,1.75}
Total: 57656 W: 7369 L: 7036 D: 43251
Ptnml(0-2): 393, 5214, 17336, 5437, 448
https://tests.stockfishchess.org/tests/view/5ee1e074f29b40b0fc95af19

SMP LTC @ 20+0.2 th 8 :
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 83576 W: 9731 L: 9341 D: 64504
Ptnml(0-2): 464, 7062, 26369, 7406, 487
https://tests.stockfishchess.org/tests/view/5ee35a21f29b40b0fc95b008

The changes were rebased on top of a successful patch by Viz (see #2734)
and two different ways of doing this were tested. The successful test
modified the constants in the patch by Viz in a similar manner to the
tuning run:

LTC (rebased) @ 60+0.6 th 1 :
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 193384 W: 24241 L: 23521 D: 145622
Ptnml(0-2): 1309, 17497, 58472, 17993, 1421
https://tests.stockfishchess.org/tests/view/5ee43319ca6c451633a995f9

Further work: the recent patch to quantize eval #2733 affects search quit
quite a bit, so doing another tune in, say, three months time might be a
good idea.

closes https://github.com/official-stockfish/Stockfish/pull/2735

Bench 4246971

diff --git a/src/search.cpp b/src/search.cpp
index f5887f3fda78fc1f6d879008b09d5f0e1ff5df8b..5ad650d2dabf25e7c809c1d967e97fa6f37fbf14 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -65,9 +65,9 @@ namespace {
   constexpr uint64_t TtHitAverageResolution = 1024;
 
   // Razor and futility margins
-  constexpr int RazorMargin = 531;
+  constexpr int RazorMargin = 516;
   Value futility_margin(Depth d, bool improving) {
-    return Value(217 * (d - improving));
+    return Value(224 * (d - improving));
   }
 
   // Reductions lookup table, initialized at startup
@@ -75,16 +75,16 @@ namespace {
 
   Depth reduction(bool i, Depth d, int mn) {
     int r = Reductions[d] * Reductions[mn];
-    return (r + 511) / 1024 + (!i && r > 1007);
+    return (r + 529) / 1024 + (!i && r > 1050);
   }
 
   constexpr int futility_move_count(bool improving, Depth depth) {
-    return (4 + depth * depth) / (2 - improving);
+    return (3 + depth * depth) / (2 - improving);
   }
 
   // History and stats update bonus, based on depth
   int stat_bonus(Depth d) {
-    return d > 15 ? -8 : 19 * d * d + 155 * d - 132;
+    return d > 15 ? 28 : 19 * d * d + 135 * d - 136;
   }
 
   // Add a small random component to draw evaluations to avoid 3fold-blindness
@@ -194,7 +194,7 @@ namespace {
 void Search::init() {
 
   for (int i = 1; i < MAX_MOVES; ++i)
-      Reductions[i] = int((24.8 + std::log(Threads.size())) * std::log(i));
+      Reductions[i] = int((24.9 + std::log(Threads.size())) * std::log(i));
 }
 
 
@@ -408,7 +408,7 @@ void Thread::search() {
               beta  = std::min(prev + delta, VALUE_INFINITE);
 
               // Adjust contempt based on root move's previousScore (dynamic contempt)
-              int dct = ct + (102 - ct / 2) * prev / (abs(prev) + 157);
+              int dct = ct + (104 - ct / 2) * prev / (abs(prev) + 143);
 
               contempt = (us == WHITE ?  make_score(dct, dct / 2)
                                       : -make_score(dct, dct / 2));
@@ -506,13 +506,13 @@ void Thread::search() {
           && !Threads.stop
           && !mainThread->stopOnPonderhit)
       {
-          double fallingEval = (332 + 6 * (mainThread->bestPreviousScore - bestValue)
-                                    + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 704.0;
+          double fallingEval = (293 + 6 * (mainThread->bestPreviousScore - bestValue)
+                                    + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 742.0;
           fallingEval = Utility::clamp(fallingEval, 0.5, 1.5);
 
           // If the bestMove is stable over several iterations, reduce time accordingly
-          timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.94 : 0.91;
-          double reduction = (1.41 + mainThread->previousTimeReduction) / (2.27 * timeReduction);
+          timeReduction = lastBestMoveDepth + 10 < completedDepth ? 1.93 : 0.96;
+          double reduction = (1.36 + mainThread->previousTimeReduction) / (2.21 * timeReduction);
 
           // Use part of the gained time from a previous stable move for the current move
           for (Thread* th : Threads)
@@ -537,7 +537,7 @@ void Thread::search() {
           }
           else if (   Threads.increaseDepth
                    && !mainThread->ponder
-                   && Time.elapsed() > totalTime * 0.6)
+                   && Time.elapsed() > totalTime * 0.57)
                    Threads.increaseDepth = false;
           else
                    Threads.increaseDepth = true;
@@ -819,10 +819,10 @@ namespace {
     // Step 9. Null move search with verification search (~40 Elo)
     if (   !PvNode
         && (ss-1)->currentMove != MOVE_NULL
-        && (ss-1)->statScore < 23397
+        && (ss-1)->statScore < 24714
         &&  eval >= beta
         &&  eval >= ss->staticEval
-        &&  ss->staticEval >= beta - 32 * depth - 30 * improving + 120 * ttPv + 292
+        &&  ss->staticEval >= beta - 29 * depth - 31 * improving + 119 * ttPv + 299
         && !excludedMove
         &&  pos.non_pawn_material(us)
         && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
@@ -830,7 +830,7 @@ namespace {
         assert(eval - beta >= 0);
 
         // Null move dynamic reduction based on depth and value
-        Depth R = (854 + 68 * depth) / 258 + std::min(int(eval - beta) / 192, 3);
+        Depth R = (793 + 70 * depth) / 252 + std::min(int(eval - beta) / 192, 3);
 
         ss->currentMove = MOVE_NULL;
         ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
@@ -870,10 +870,10 @@ namespace {
     // If we have a good enough capture and a reduced search returns a value
     // much above beta, we can (almost) safely prune the previous move.
     if (   !PvNode
-        &&  depth >= 5
+        &&  depth > 5
         &&  abs(beta) < VALUE_TB_WIN_IN_MAX_PLY)
     {
-        Value raisedBeta = beta + 189 - 45 * improving;
+        Value raisedBeta = beta + 182 - 48 * improving;
         assert(raisedBeta < VALUE_INFINITE);
         MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &captureHistory);
         int probCutCount = 0;
@@ -904,7 +904,7 @@ namespace {
 
                 // If the qsearch held, perform the regular search
                 if (value >= raisedBeta)
-                    value = -search<NonPV>(pos, ss+1, -raisedBeta, -raisedBeta+1, depth - 4, !cutNode);
+                    value = -search<NonPV>(pos, ss+1, -raisedBeta, -raisedBeta+1, depth - 5, !cutNode);
 
                 pos.undo_move(move);
 
@@ -1003,15 +1003,15 @@ moves_loop: // When in check, search starts from here
               // Futility pruning: parent node (~5 Elo)
               if (   lmrDepth < 6
                   && !ss->inCheck
-                  && ss->staticEval + 235 + 172 * lmrDepth <= alpha
+                  && ss->staticEval + 252 + 176 * lmrDepth <= alpha
                   &&  (*contHist[0])[movedPiece][to_sq(move)]
                     + (*contHist[1])[movedPiece][to_sq(move)]
                     + (*contHist[3])[movedPiece][to_sq(move)]
-                    + (*contHist[5])[movedPiece][to_sq(move)] / 2 < 31400)
+                    + (*contHist[5])[movedPiece][to_sq(move)] / 2 < 30251)
                   continue;
 
               // Prune moves with negative SEE (~20 Elo)
-              if (!pos.see_ge(move, Value(-(32 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
+              if (!pos.see_ge(move, Value(-(31 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
                   continue;
           }
           else
@@ -1027,11 +1027,11 @@ moves_loop: // When in check, search starts from here
                   && lmrDepth < 6
                   && !(PvNode && abs(bestValue) < 2)
                   && !ss->inCheck
-                  && ss->staticEval + 270 + 384 * lmrDepth + PieceValue[MG][type_of(pos.piece_on(to_sq(move)))] <= alpha)
+                  && ss->staticEval + 264 + 397 * lmrDepth + PieceValue[MG][type_of(pos.piece_on(to_sq(move)))] <= alpha)
                   continue;
 
               // See based pruning
-              if (!pos.see_ge(move, Value(-194) * depth)) // (~25 Elo)
+              if (!pos.see_ge(move, Value(-192) * depth)) // (~25 Elo)
                   continue;
           }
       }
@@ -1144,12 +1144,12 @@ moves_loop: // When in check, search starts from here
               || moveCountPruning
               || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
               || cutNode
-              || thisThread->ttHitAverage < 375 * TtHitAverageResolution * TtHitAverageWindow / 1024))
+              || thisThread->ttHitAverage < 399 * TtHitAverageResolution * TtHitAverageWindow / 1024))
       {
           Depth r = reduction(improving, depth, moveCount);
 
           // Decrease reduction if the ttHit running average is large
-          if (thisThread->ttHitAverage > 500 * TtHitAverageResolution * TtHitAverageWindow / 1024)
+          if (thisThread->ttHitAverage > 492 * TtHitAverageResolution * TtHitAverageWindow / 1024)
               r--;
 
           // Reduction if other threads are searching this position.
@@ -1195,14 +1195,14 @@ moves_loop: // When in check, search starts from here
                              - 4926;
 
               // Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
-              if (ss->statScore >= -102 && (ss-1)->statScore < -114)
+              if (ss->statScore >= -99 && (ss-1)->statScore < -116)
                   r--;
 
-              else if ((ss-1)->statScore >= -116 && ss->statScore < -154)
+              else if ((ss-1)->statScore >= -117 && ss->statScore < -150)
                   r++;
 
               // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
-              r -= ss->statScore / 16434;
+              r -= ss->statScore / 15896;
           }
           else
           {
@@ -1474,7 +1474,7 @@ moves_loop: // When in check, search starts from here
         if (PvNode && bestValue > alpha)
             alpha = bestValue;
 
-        futilityBase = bestValue + 154;
+        futilityBase = bestValue + 138;
     }
 
     const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,