LMR simplification

locutus2 · snicolet · commit 198418ee6789 · 2018-08-09T14:45:35.000+02:00
Unify the "quiet" and "non-quiet" reduction rules for use at any kind of moves. The idea behind it was that both rules reduce at similiar cases in master: one directly for late previous moves and the other indirectly by using a bad stat score which is used for most move sorting and so approximates the late move condition. For captures/promotions the old rule was triggered in 25% but the new rule only for 3% of all cases (so now more reductions are done, whereas for quiet moves reductions keep the same level). STC: LLR: 2.95 (-2.94,2.94) [-3.00,1.00] Total: 162327 W: 35976 L: 36134 D: 90217 http://tests.stockfishchess.org/tests/view/5b6a9a430ebc5902bdb9d5c1 LTC: LLR: 2.96 (-2.94,2.94) [-3.00,1.00] Total: 29570 W: 5083 L: 4976 D: 19511 http://tests.stockfishchess.org/tests/view/5b6bc5d00ebc5902bdb9e9d6 Bench: 4526980
diff --git a/src/search.cpp b/src/search.cpp
@@ -998,18 +998,12 @@ namespace {
       {
           Depth r = reduction<PvNode>(improving, depth, moveCount);
 
-          if (captureOrPromotion) // (~5 Elo)
-          {
-              // Decrease reduction by comparing opponent's stat score
-              if ((ss-1)->statScore < 0)
-                  r -= ONE_PLY;
-          }
-          else
-          {
-              // Decrease reduction if opponent's move count is high (~5 Elo)
-              if ((ss-1)->moveCount > 15)
-                  r -= ONE_PLY;
+          // Decrease reduction if opponent's move count is high (~10 Elo)
+          if ((ss-1)->moveCount > 15)
+              r -= ONE_PLY;
 
+          if (!captureOrPromotion)
+          {
               // Decrease reduction for exact PV nodes (~0 Elo)
               if (pvExact)
                   r -= ONE_PLY;
