Reorder conditions in LMR and pruning
authorVizvezdenec <Vizvezdenec@gmail.com>
Fri, 1 Jan 2021 09:59:35 +0000 (12:59 +0300)
committerJoost VandeVondele <Joost.VandeVondele@gmail.com>
Fri, 8 Jan 2021 15:57:26 +0000 (16:57 +0100)
Make code logic somewhat easier to follow.

closes https://github.com/official-stockfish/Stockfish/pull/3285

No functional change.

src/search.cpp

index e2c3f584eedc53201fac6d06c33e184e0dae4b14..9ea77b3a4353c9808c2a8ce0139b2b833ba481a6 100644 (file)
@@ -1039,8 +1039,20 @@ moves_loop: // When in check, search starts from here
           // Reduced depth of the next LMR search
           int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
 
-          if (   !captureOrPromotion
-              && !givesCheck)
+          if (   captureOrPromotion
+              || givesCheck)
+          {
+              // Capture history based pruning when the move doesn't give check
+              if (   !givesCheck
+                  && lmrDepth < 1
+                  && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0)
+                  continue;
+
+              // SEE based pruning
+              if (!pos.see_ge(move, Value(-218) * depth)) // (~25 Elo)
+                  continue;
+          }
+          else
           {
               // Countermoves based pruning (~20 Elo)
               if (   lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
@@ -1062,18 +1074,6 @@ moves_loop: // When in check, search starts from here
               if (!pos.see_ge(move, Value(-(30 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
                   continue;
           }
-          else
-          {
-              // Capture history based pruning when the move doesn't give check
-              if (   !givesCheck
-                  && lmrDepth < 1
-                  && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0)
-                  continue;
-
-              // SEE based pruning
-              if (!pos.see_ge(move, Value(-218) * depth)) // (~25 Elo)
-                  continue;
-          }
       }
 
       // Step 13. Extensions (~75 Elo)
@@ -1192,7 +1192,14 @@ moves_loop: // When in check, search starts from here
           if (singularQuietLMR)
               r--;
 
-          if (!captureOrPromotion)
+          if (captureOrPromotion)
+          {
+              // Unless giving check, this capture is likely bad
+              if (   !givesCheck
+                  && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 210 * depth <= alpha)
+                  r++;
+          }
+          else
           {
               // Increase reduction if ttMove is a capture (~5 Elo)
               if (ttCapture)
@@ -1228,13 +1235,6 @@ moves_loop: // When in check, search starts from here
               // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
               r -= ss->statScore / 14884;
           }
-          else
-          {
-              // Unless giving check, this capture is likely bad
-              if (   !givesCheck
-                  && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 210 * depth <= alpha)
-                  r++;
-          }
 
           Depth d = std::clamp(newDepth - r, 1, newDepth);