Streamline null search reduction formula

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 9c1d0b5eca66e1e928accfaec998d3f3d426d2d1..72ab9a1228d36bc58deb8d40e0c92c45fb896f87 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -708,16 +708,16 @@ namespace {
         ss->currentMove = MOVE_NULL;
 
         // Null move dynamic reduction based on depth
         ss->currentMove = MOVE_NULL;
 
         // Null move dynamic reduction based on depth

-        int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
+        Depth R = 3 * ONE_PLY + depth / 4;

 
         // Null move dynamic reduction based on value
         if (refinedValue - PawnValueMidgame > beta)
 
         // Null move dynamic reduction based on value
         if (refinedValue - PawnValueMidgame > beta)

-            R++;
+            R += ONE_PLY;

 
         pos.do_null_move<true>(st);
         (ss+1)->skipNullMove = true;
 
         pos.do_null_move<true>(st);
         (ss+1)->skipNullMove = true;

-        nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
-                                              : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
+        nullValue = depth-R < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
+                                      : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R);

         (ss+1)->skipNullMove = false;
         pos.do_null_move<false>(st);
 
         (ss+1)->skipNullMove = false;
         pos.do_null_move<false>(st);
 


@@ -732,7 +732,7 @@ namespace {
 
             // Do verification search at high depths
             ss->skipNullMove = true;
 
             // Do verification search at high depths
             ss->skipNullMove = true;

-            Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
+            Value v = search<NonPV>(pos, ss, alpha, beta, depth-R);

             ss->skipNullMove = false;
 
             if (v >= beta)
             ss->skipNullMove = false;
 
             if (v >= beta)