Reintroduce doEvenDeeperSearch

This patch is basically the same as a reverted patch
but now has some guarding against search being stuck - the same
way as we do with double extensions. This should help with
search explosions - albeit slowly but they eventually should be resolved.

passed STC:
https://tests.stockfishchess.org/tests/view/639733d0b4e52c95053f3485
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 514048 W: 136423 L: 135435 D: 242190
Ptnml(0-2): 1425, 56945, 139420, 57685, 1549

passed LTC:
https://tests.stockfishchess.org/tests/view/639ab79b93ed41c57eded5c3
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 113800 W: 30642 L: 30190 D: 52968
Ptnml(0-2): 53, 11092, 34178, 11504, 73

closes https://github.com/official-stockfish/Stockfish/pull/4287

bench 3611278

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 6a0fae9e9bac0f3f58a412f8e415e014b6e509dc..7619398e01fcb9f334a519c92999f2c967e6b438 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -1063,7 +1063,7 @@ Value Eval::evaluate(const Position& pos, int* complexity) {
   else
   {
       int nnueComplexity;
-      int scale = 1064 + 106 * pos.non_pawn_material() / 5120;
+      int scale = 1076 + 96 * pos.non_pawn_material() / 5120;
 
       Color stm = pos.side_to_move();
       Value optimism = pos.this_thread()->optimism[stm];
@@ -1071,8 +1071,8 @@ Value Eval::evaluate(const Position& pos, int* complexity) {
       Value nnue = NNUE::evaluate(pos, true, &nnueComplexity);
 
       // Blend nnue complexity with (semi)classical complexity
-      nnueComplexity = (  416 * nnueComplexity
-                        + 424 * abs(psq - nnue)
+      nnueComplexity = (  412 * nnueComplexity
+                        + 428 * abs(psq - nnue)
                         + (optimism  > 0 ? int(optimism) * int(psq - nnue) : 0)
                         ) / 1024;
 
@@ -1080,12 +1080,12 @@ Value Eval::evaluate(const Position& pos, int* complexity) {
       if (complexity)
           *complexity = nnueComplexity;
 
-      optimism = optimism * (269 + nnueComplexity) / 256;
-      v = (nnue * scale + optimism * (scale - 754)) / 1024;
+      optimism = optimism * (278 + nnueComplexity) / 256;
+      v = (nnue * scale + optimism * (scale - 755)) / 1024;
   }
 
   // Damp down the evaluation linearly when shuffling
-  v = v * (195 - pos.rule50_count()) / 211;
+  v = v * (197 - pos.rule50_count()) / 214;
 
   // Guarantee evaluation does not hit the tablebase range
   v = std::clamp(v, VALUE_TB_LOSS_IN_MAX_PLY + 1, VALUE_TB_WIN_IN_MAX_PLY - 1);

diff --git a/src/search.cpp b/src/search.cpp
index b58a344a597b61103c809706c4893aff48451553..4507460a5b639e40573e6af83e35b6f70eaa6767 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -81,7 +81,7 @@ namespace {
 
   // History and stats update bonus, based on depth
   int stat_bonus(Depth d) {
-    return std::min((12 * d + 282) * d - 349 , 1594);
+    return std::min((12 * d + 282) * d - 349 , 1480);
   }
 
   // Add a small random component to draw evaluations to avoid 3-fold blindness
@@ -1066,7 +1066,7 @@ moves_loop: // When in check, search starts here
                   // Avoid search explosion by limiting the number of double extensions
                   if (  !PvNode
                       && value < singularBeta - 25
-                      && ss->doubleExtensions <= 9)
+                      && ss->doubleExtensions <= 10)
                   {
                       extension = 2;
                       depth += depth < 12;
@@ -1175,7 +1175,7 @@ moves_loop: // When in check, search starts here
                          - 4433;
 
           // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
-          r -= ss->statScore / (13628 + 4000 * (depth > 7 && depth < 19));
+          r -= ss->statScore / (13000 + 4152 * (depth > 7 && depth < 19));
 
           // In general we want to cap the LMR depth search at newDepth, but when
           // reduction is negative, we allow this move a limited search extension
@@ -1190,9 +1190,12 @@ moves_loop: // When in check, search starts here
               // Adjust full depth search based on LMR results - if result
               // was good enough search deeper, if it was bad enough search shallower
               const bool doDeeperSearch = value > (alpha + 64 + 11 * (newDepth - d));
+              const bool doEvenDeeperSearch = value > alpha + 582 && ss->doubleExtensions <= 5;
               const bool doShallowerSearch = value < bestValue + newDepth;
 
-              newDepth += doDeeperSearch - doShallowerSearch;
+              ss->doubleExtensions = ss->doubleExtensions + doEvenDeeperSearch;
+
+              newDepth += doDeeperSearch - doShallowerSearch + doEvenDeeperSearch;
 
               if (newDepth > d)
                   value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);