Document asymmetric SEE pruning trick

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 60667c8764e32a01f904477e66ad614b57b73b57..5abbafbcbfcd8b756dbf481efdffff9187e78016 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -679,7 +679,7 @@ namespace {
             if (nullValue >= VALUE_MATE_IN_MAX_PLY)
                 nullValue = beta;
 
-            if (depth < 6 * ONE_PLY)
+            if (depth < 12 * ONE_PLY)
                 return nullValue;
 
             // Do verification search at high depths
@@ -1225,10 +1225,11 @@ split_point_start: // At split points actual search starts from here
               continue;
           }
 
-          // Prune moves with negative or equal SEE
+          // Prune moves with negative or equal SEE.
+          // Also prune moves with positive SEE where capturing loses a tempo and SEE < beta - futilityBase.
           if (   futilityBase < beta
               && depth < DEPTH_ZERO
-              && pos.see(move) <= 0)
+              && pos.see_asymm(move, beta - futilityBase) <= 0)
           {
               bestValue = std::max(bestValue, futilityBase);
               continue;