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 #2735

Bench 4246971

src/search.cpp

@@ -65,26 +65,26 @@ 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
  int Reductions[MAX_MOVES]; // [depth or moveNumber]
 
  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;
@@ -819,18 +819,18 @@ 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))
  {
  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 @@ namespace {
  // 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 @@ namespace {
  && 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 @@ namespace {
  || 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 @@ namespace {
  - 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 @@ namespace {
  if (PvNode && bestValue > alpha)
  alpha = bestValue;
 
- futilityBase = bestValue + 154;
+ futilityBase = bestValue + 138;
  }
 
  const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,