Remove log depth reduction terms.

locutus2 · vondele · commit d11f49b79042 · 2025-08-24T19:30:31.000+02:00
Motivated by the elo loss of last VVLTC regression test i remove the new log depth reductions (tuned at STC) to regain strength at VVLTC. The constant terms are adjusted based on the old values and the changes from the last added VVLTC tuning. Passed VVLTC with STC bound: LLR: 2.95 (-2.94,2.94) <0.00,2.00> Total: 53802 W: 14030 L: 13740 D: 26032 Ptnml(0-2): 5, 4924, 16754, 5212, 6 https://tests.stockfishchess.org/tests/view/68a9a9f575da51a345a5a675 Passed VVLTC with LTC bound: LLR: 2.94 (-2.94,2.94) <0.50,2.50> Total: 53658 W: 14022 L: 13699 D: 25937 Ptnml(0-2): 3, 4894, 16712, 5217, 3 https://tests.stockfishchess.org/tests/view/68a8d2b2b6fb3300203bca77 closes #6257 Bench: 2566780
diff --git a/src/search.cpp b/src/search.cpp
@@ -1177,27 +1177,27 @@ Value Search::Worker::search(
 
         // These reduction adjustments have no proven non-linear scaling
 
-        r += 700 - 6 * msb(depth);  // Base reduction offset to compensate for other tweaks
-        r -= moveCount * (64 - 2 * msb(depth));
+        r += 671;  // Base reduction offset to compensate for other tweaks
+        r -= moveCount * 66;
         r -= std::abs(correctionValue) / 30450;
 
         // Increase reduction for cut nodes
         if (cutNode)
-            r += 3092 + 2 * msb(depth) + (980 + 15 * msb(depth)) * !ttData.move;
+            r += 3094 + 1056 * !ttData.move;
 
         // Increase reduction if ttMove is a capture
         if (ttCapture)
-            r += 1467 - 40 * msb(depth);
+            r += 1415;
 
         // Increase reduction if next ply has a lot of fail high
         if ((ss + 1)->cutoffCnt > 2)
-            r += 1041 + 34 * msb(depth) + allNode * (752 + 226 * msb(depth));
+            r += 1051 + allNode * 814;
 
         r += (ss + 1)->quietMoveStreak * 50;
 
         // For first picked move (ttMove) reduce reduction
         if (move == ttData.move)
-            r -= 2096 + 27 * msb(depth);
+            r -= 2018;
 
         if (capture)
             ss->statScore = 803 * int(PieceValue[pos.captured_piece()]) / 128
@@ -1208,7 +1208,7 @@ Value Search::Worker::search(
                           + (*contHist[1])[movedPiece][move.to_sq()];
 
         // Decrease/increase reduction for moves with a good/bad history
-        r -= ss->statScore * (734 - 12 * msb(depth)) / 8192;
+        r -= ss->statScore * 794 / 8192;
 
         // Step 17. Late moves reduction / extension (LMR)
         if (depth >= 2 && moveCount > 1)
@@ -1250,7 +1250,7 @@ Value Search::Worker::search(
         {
             // Increase reduction if ttMove is not present
             if (!ttData.move)
-                r += 1178 + 35 * msb(depth);
+                r += 1118;
 
             if (depth < 5)
                 r += 1080;
