Cleanup comments and some code reorg.

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 4b390713d8d3c721d720c79497c2a556cd63b0ea..ad4b458e180b26d3a0772d277776d7a077a716c2 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -379,8 +379,8 @@ void Thread::search() {
             int failedHighCnt = 0;
             while (true)
             {
-                // Adjust the effective depth searched, but ensure at least one effective increment for every
-                // four searchAgain steps (see issue #2717).
+                // Adjust the effective depth searched, but ensure at least one effective increment
+                // for every four searchAgain steps (see issue #2717).
                 Depth adjustedDepth =
                   std::max(1, rootDepth - failedHighCnt - 3 * (searchAgainCounter + 1) / 4);
                 bestValue = Stockfish::search<Root>(rootPos, ss, alpha, beta, adjustedDepth, false);
@@ -633,7 +633,8 @@ Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, boo
                 if (!ttCapture)
                     update_quiet_stats(pos, ss, ttMove, stat_bonus(depth));
 
-                // Extra penalty for early quiet moves of the previous ply (~0 Elo on STC, ~2 Elo on LTC)
+                // Extra penalty for early quiet moves of
+                // the previous ply (~0 Elo on STC, ~2 Elo on LTC).
                 if (prevSq != SQ_NONE && (ss - 1)->moveCount <= 2 && !priorCapture)
                     update_continuation_histories(ss - 1, pos.piece_on(prevSq), prevSq,
                                                   -stat_bonus(depth + 1));
@@ -715,7 +716,8 @@ Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, boo
     }
     else if (excludedMove)
     {
-        // Providing the hint that this node's accumulator will be used often brings significant Elo gain (~13 Elo)
+        // Providing the hint that this node's accumulator will be used often
+        // brings significant Elo gain (~13 Elo).
         Eval::NNUE::hint_common_parent_position(pos);
         eval = ss->staticEval;
     }
@@ -817,8 +819,9 @@ Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, boo
         }
     }
 
-    // Step 10. If the position doesn't have a ttMove, decrease depth by 2
-    // (or by 4 if the TT entry for the current position was hit and the stored depth is greater than or equal to the current depth).
+    // Step 10. If the position doesn't have a ttMove, decrease depth by 2,
+    // or by 4 if the TT entry for the current position was hit and
+    // the stored depth is greater than or equal to the current depth.
     // Use qsearch if depth is equal or below zero (~9 Elo)
     if (PvNode && !ttMove)
         depth -= 2 + 2 * (ss->ttHit && tte->depth() >= depth);
@@ -967,13 +970,15 @@ moves_loop:  // When in check, search starts here
             if (capture || givesCheck)
             {
                 // Futility pruning for captures (~2 Elo)
-                if (!givesCheck && lmrDepth < 7 && !ss->inCheck
-                    && ss->staticEval + 188 + 206 * lmrDepth + PieceValue[pos.piece_on(to_sq(move))]
-                           + captureHistory[movedPiece][to_sq(move)]
-                                           [type_of(pos.piece_on(to_sq(move)))]
-                               / 7
-                         < alpha)
-                    continue;
+                if (!givesCheck && lmrDepth < 7 && !ss->inCheck)
+                {
+                    Piece capturedPiece = pos.piece_on(to_sq(move));
+                    int   futilityEval =
+                      ss->staticEval + 188 + 206 * lmrDepth + PieceValue[capturedPiece]
+                      + captureHistory[movedPiece][to_sq(move)][type_of(capturedPiece)] / 7;
+                    if (futilityEval < alpha)
+                        continue;
+                }
 
                 // SEE based pruning for captures and checks (~11 Elo)
                 if (!pos.see_ge(move, Value(-185) * depth))
@@ -1018,9 +1023,9 @@ moves_loop:  // When in check, search starts here
             // that depth margin and singularBeta margin are known for having non-linear
             // scaling. Their values are optimized to time controls of 180+1.8 and longer
             // so changing them requires tests at this type of time controls.
-            if (!rootNode
+            // Recursive singular search is avoided.
+            if (!rootNode && move == ttMove && !excludedMove
                 && depth >= 4 - (thisThread->completedDepth > 24) + 2 * (PvNode && tte->is_pv())
-                && move == ttMove && !excludedMove  // Avoid recursive singular search
                 && abs(ttValue) < VALUE_TB_WIN_IN_MAX_PLY && (tte->bound() & BOUND_LOWER)
                 && tte->depth() >= depth - 3)
             {
@@ -1053,7 +1058,7 @@ moves_loop:  // When in check, search starts here
                 else if (singularBeta >= beta)
                     return singularBeta;
 
-                // If the eval of ttMove is greater than beta, we reduce it (negative extension) (~7 Elo)
+                // If the eval of ttMove is greater than beta, reduce it (negative extension) (~7 Elo)
                 else if (ttValue >= beta)
                     extension = -2 - !PvNode;
 
@@ -1061,7 +1066,7 @@ moves_loop:  // When in check, search starts here
                 else if (cutNode)
                     extension = depth < 19 ? -2 : -1;
 
-                // If the eval of ttMove is less than value, we reduce it (negative extension) (~1 Elo)
+                // If the eval of ttMove is less than value, reduce it (negative extension) (~1 Elo)
                 else if (ttValue <= value)
                     extension = -1;
             }