From: FauziAkram <fauzi.dabat@hotmail.com>
Date: Wed, 5 Apr 2023 21:35:05 +0000 (+0300)
Subject: Depth Tweak and tuning
X-Git-Url: https://git.sesse.net/?a=commitdiff_plain;ds=sidebyside;h=59f2085469a7dd96146905a5d8d0c1a5d987187d;p=stockfish

Depth Tweak and tuning

tunes reduction related parameters, and introduces more reduction on found good moves.

credit for this patch goes also to candirufish Yoshie2000 dubslow peregrineshahin Vizvezdenec

Passed STC:
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 38424 W: 10346 L: 10040 D: 18038
Ptnml(0-2): 103, 4111, 10473, 4427, 98
https://tests.stockfishchess.org/tests/view/642ca74277ff3301150db511

Passed LTC:
LLR: 2.97 (-2.94,2.94) <0.50,2.50>
Total: 136968 W: 37151 L: 36660 D: 63157
Ptnml(0-2): 43, 13052, 41808, 13533, 48
https://tests.stockfishchess.org/tests/view/642d632377ff3301150dddbe

closes https://github.com/official-stockfish/Stockfish/pull/4499

bench: 3672914
---

diff --git a/src/search.cpp b/src/search.cpp
index aa1a3e8c..fba9685b 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -72,7 +72,7 @@ namespace {
 
   Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) {
     int r = Reductions[d] * Reductions[mn];
-    return (r + 1449 - int(delta) * 1001 / int(rootDelta)) / 1024 + (!i && r > 941);
+    return (r + 1449 - int(delta) * 937 / int(rootDelta)) / 1024 + (!i && r > 941);
   }
 
   constexpr int futility_move_count(bool improving, Depth depth) {
@@ -82,7 +82,7 @@ namespace {
 
   // History and stats update bonus, based on depth
   int stat_bonus(Depth d) {
-    return std::min(341 * d - 470, 1855);
+    return std::min(341 * d - 470, 1710);
   }
 
   // Add a small random component to draw evaluations to avoid 3-fold blindness
@@ -775,7 +775,7 @@ namespace {
     // 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 - 426 - 252 * depth * depth)
+    if (eval < alpha - 426 - 256 * depth * depth)
     {
         value = qsearch<NonPV>(pos, ss, alpha - 1, alpha);
         if (value < alpha)
@@ -797,7 +797,7 @@ namespace {
         && (ss-1)->statScore < 18755
         &&  eval >= beta
         &&  eval >= ss->staticEval
-        &&  ss->staticEval >= beta - 19 * depth - improvement / 13 + 253 + complexity / 25
+        &&  ss->staticEval >= beta - 20 * depth - improvement / 13 + 253 + complexity / 25
         && !excludedMove
         &&  pos.non_pawn_material(us)
         && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
@@ -805,7 +805,7 @@ namespace {
         assert(eval - beta >= 0);
 
         // Null move dynamic reduction based on depth, eval and complexity of position
-        Depth R = std::min(int(eval - beta) / 168, 6) + depth / 3 + 4 - (complexity > 825);
+        Depth R = std::min(int(eval - beta) / 172, 6) + depth / 3 + 4 - (complexity > 825);
 
         ss->currentMove = MOVE_NULL;
         ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
@@ -1333,16 +1333,18 @@ moves_loop: // When in check, search starts here
 
               if (PvNode && value < beta) // Update alpha! Always alpha < beta
               {
-                  alpha = value;
 
                   // Reduce other moves if we have found at least one score improvement (~1 Elo)
                   if (   depth > 1
-                      && depth < 6
-                      && beta  <  10534
-                      && alpha > -10534)
-                      depth -= 1;
+                      && ((improving && complexity > 971) || (value < (5 * alpha + 75 * beta) / 87) || depth < 6)
+                      && beta  <  12535
+                      && value > -12535) {
+                      bool extraReduction = depth > 2 && alpha > -12535 && bestValue != -VALUE_INFINITE && (value - bestValue) > (7 * (beta - alpha)) / 8;
+                      depth -= 1 + extraReduction;
+                  }
 
                   assert(depth > 0);
+                  alpha = value;
               }
               else
               {