Simplify NMP reduction formula

FauziAkram · vondele · commit df88db16c611 · 2025-11-14T17:24:16.000+01:00
Passed STC: LLR: 2.97 (-2.94,2.94) <-1.75,0.25> Total: 178912 W: 46625 L: 46559 D: 85728 Ptnml(0-2): 540, 21167, 45975, 21235, 539 https://tests.stockfishchess.org/tests/view/69060677ea4b268f1fac1f25 Passed LTC: LLR: 2.99 (-2.94,2.94) <-1.75,0.25> Total: 140988 W: 36278 L: 36176 D: 68534 Ptnml(0-2): 82, 15520, 39215, 15568, 109 https://tests.stockfishchess.org/tests/view/6908bc32ea4b268f1fac288f closes #6416 bench: 2959834
diff --git a/src/search.cpp b/src/search.cpp
@@ -872,7 +872,7 @@ Value Search::Worker::search(
         assert((ss - 1)->currentMove != Move::null());
 
         // Null move dynamic reduction based on depth
-        Depth R = 6 + depth / 3 + improving;
+        Depth R = 7 + depth / 3;
         do_null_move(pos, st, ss);
 
         Value nullValue = -search<NonPV>(pos, ss + 1, -beta, -beta + 1, depth - R, false);
