Do shallower search in case of lmr being not successful enough

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 3c2ae3e52df8b0c43f8cc05a132c2adb801bef81..5839763dc7fd647fa8e91d92cb874e54368c1126 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -309,7 +309,6 @@ void Thread::search() {
 
   complexityAverage.set(155, 1);
 
-  trend = SCORE_ZERO;
   optimism[us] = optimism[~us] = VALUE_ZERO;
 
   int searchAgainCounter = 0;
@@ -356,11 +355,7 @@ void Thread::search() {
               alpha = std::max(prev - delta,-VALUE_INFINITE);
               beta  = std::min(prev + delta, VALUE_INFINITE);
 
-              // Adjust trend and optimism based on root move's previousScore
-              int tr = 116 * prev / (std::abs(prev) + 89);
-              trend = (us == WHITE ?  make_score(tr, tr / 2)
-                                   : -make_score(tr, tr / 2));
-
+              // Adjust optimism based on root move's previousScore
               int opt = 118 * prev / (std::abs(prev) + 169);
               optimism[ us] = Value(opt);
               optimism[~us] = -optimism[us];
@@ -775,8 +770,7 @@ namespace {
     // Step 7. Razoring.
     // If eval is really low check with qsearch if it can exceed alpha, if it can't,
     // return a fail low.
-    if (   depth <= 7
-        && eval < alpha - 369 - 254 * depth * depth)
+    if (eval < alpha - 369 - 254 * depth * depth)
     {
         value = qsearch<NonPV>(pos, ss, alpha - 1, alpha);
         if (value < alpha)
@@ -1178,7 +1172,7 @@ 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;
+          r -= ss->statScore / (13628 + 4000 * (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
@@ -1190,8 +1184,11 @@ moves_loop: // When in check, search starts here
           // Do full depth search when reduced LMR search fails high
           if (value > alpha && d < newDepth)
           {
+              // 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));
-              value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth + doDeeperSearch, !cutNode);
+              const bool doShallowerSearch = value < bestValue + newDepth;
+              value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth + doDeeperSearch - doShallowerSearch, !cutNode);
 
               int bonus = value > alpha ?  stat_bonus(newDepth)
                                         : -stat_bonus(newDepth);