Enhance some comments

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 6e719be82f4a719a7c9810c5ea3907967c8cf2f8..483412c598a870cf6d78bde0175109f5f505abf9 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -745,6 +745,8 @@ Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, boo
     {
         int bonus = std::clamp(-18 * int((ss - 1)->staticEval + ss->staticEval), -1812, 1812);
         thisThread->mainHistory[~us][from_to((ss - 1)->currentMove)] << bonus;
+        if (type_of(pos.piece_on(prevSq)) != PAWN && type_of((ss - 1)->currentMove) != PROMOTION)
+            thisThread->pawnHistory[pawn_structure(pos)][pos.piece_on(prevSq)][prevSq] << bonus / 4;
     }
 
     // Set up the improving flag, which is true if current static evaluation is
@@ -764,18 +766,7 @@ Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, boo
     {
         value = qsearch<NonPV>(pos, ss, alpha - 1, alpha);
         if (value < alpha)
-        {
-            if (!priorCapture && prevSq != SQ_NONE)
-            {
-                int bonus = (depth > 6) + (PvNode || cutNode) + (value < alpha - 658)
-                          + ((ss - 1)->moveCount > 11);
-                update_continuation_histories(ss - 1, pos.piece_on(prevSq), prevSq,
-                                              stat_bonus(depth) * bonus);
-                thisThread->mainHistory[~us][from_to((ss - 1)->currentMove)]
-                  << stat_bonus(depth) * bonus * 57 / 100;
-            }
             return value;
-        }
     }
 
     // Step 8. Futility pruning: child node (~40 Elo)
@@ -1018,7 +1009,10 @@ moves_loop:  // When in check, search starts here
                 lmrDepth = std::max(lmrDepth, -1);
 
                 // Futility pruning: parent node (~13 Elo)
-                if (!ss->inCheck && lmrDepth < 13 && ss->staticEval + 77 + 124 * lmrDepth <= alpha)
+                if (!ss->inCheck && lmrDepth < 13
+                    && ss->staticEval + (bestValue < ss->staticEval - 62 ? 123 : 77)
+                           + 127 * lmrDepth
+                         <= alpha)
                     continue;
 
                 lmrDepth = std::max(lmrDepth, 0);
@@ -1036,9 +1030,10 @@ moves_loop:  // When in check, search starts here
             // Singular extension search (~94 Elo). If all moves but one fail low on a
             // search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
             // then that move is singular and should be extended. To verify this we do
-            // a reduced search on all the other moves but the ttMove and if the result
-            // is lower than ttValue minus a margin, then we will extend the ttMove. Note
-            // that depth margin and singularBeta margin are known for having non-linear
+            // a reduced search on the position excluding the ttMove and if the result
+            // is lower than ttValue minus a margin, then we will extend the ttMove.
+
+            // Note: the 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.
             // Recursive singular search is avoided.
@@ -1069,22 +1064,28 @@ moves_loop:  // When in check, search starts here
                 }
 
                 // Multi-cut pruning
-                // Our ttMove is assumed to fail high, and now we failed high also on a
-                // reduced search without the ttMove. So we assume this expected cut-node
-                // is not singular, that multiple moves fail high, and we can prune the
-                // whole subtree by returning a softbound.
+                // Our ttMove is assumed to fail high based on the bound of the TT entry,
+                // and if after excluding the ttMove with a reduced search we fail high over the original beta,
+                // we assume this expected cut-node is not singular (multiple moves fail high),
+                // and we can prune the whole subtree by returning a softbound.
                 else if (singularBeta >= beta)
                     return singularBeta;
 
-                // If the eval of ttMove is greater than beta, reduce it (negative extension) (~7 Elo)
+                // Negative extensions
+                // If other moves failed high over (ttValue - margin) without the ttMove on a reduced search,
+                // but we cannot do multi-cut because (ttValue - margin) is lower than the original beta,
+                // we do not know if the ttMove is singular or can do a multi-cut,
+                // so we reduce the ttMove in favor of other moves based on some conditions:
+
+                // If the ttMove is assumed to fail high over currnet beta (~7 Elo)
                 else if (ttValue >= beta)
                     extension = -2 - !PvNode;
 
-                // If we are on a cutNode, reduce it based on depth (negative extension) (~1 Elo)
+                // If we are on a cutNode but the ttMove is not assumed to fail high over current beta (~1 Elo)
                 else if (cutNode)
                     extension = depth < 19 ? -2 : -1;
 
-                // If the eval of ttMove is less than value, reduce it (negative extension) (~1 Elo)
+                // If the ttMove is assumed to fail low over the value of the reduced search (~1 Elo)
                 else if (ttValue <= value)
                     extension = -1;
             }
@@ -1339,7 +1340,7 @@ moves_loop:  // When in check, search starts here
         update_continuation_histories(ss - 1, pos.piece_on(prevSq), prevSq,
                                       stat_bonus(depth) * bonus);
         thisThread->mainHistory[~us][from_to((ss - 1)->currentMove)]
-          << stat_bonus(depth) * bonus * 61 / 100;
+          << stat_bonus(depth) * bonus / 2;
     }
 
     if (PvNode)
@@ -1417,9 +1418,7 @@ Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
 
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
 
-    // Decide whether or not to include checks: this fixes also the type of
-    // TT entry depth that we are going to use. Note that in qsearch we use
-    // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
+    // Decide the replacement and cutoff priority of the qsearch TT entries
     ttDepth = ss->inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS;
 
     // Step 3. Transposition table lookup