Synchronize search_pv() with search take II

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 6fd99763e46a0a007a82ba4c86b07f7cdd1462a0..a052ea18f8828d3c56c8dc8cee94c0cde34bcbcc 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1123,7 +1123,7 @@ namespace {
       moveIsCheck = pos.move_is_check(move, ci);
       captureOrPromotion = pos.move_is_capture_or_promotion(move);
 
-      // Decide the new search depth
+      // Step 11. Decide the new search depth
       ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
 
       // Singular extension search. We extend the TT move if its value is much better than
@@ -1149,17 +1149,21 @@ namespace {
 
       newDepth = depth - OnePly + ext;
 
-      // Update current move
+      // Update current move (this must be done after singular extension search)
       movesSearched[moveCount++] = ss[ply].currentMove = move;
 
-      // Make and search the move
+      // Step 12. Futility pruning (is omitted in PV nodes)
+
+      // Step 13. Make the move
       pos.do_move(move, st, ci, moveIsCheck);
 
-      if (moveCount == 1) // The first move in list is the PV
+      // Step extra. pv search (only in PV nodes)
+      // The first move in list is the expected PV
+      if (moveCount == 1)
           value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
       else
       {
-        // Try to reduce non-pv search depth by one ply if move seems not problematic,
+        // Step 14. Reduced search
         // if the move fails high will be re-searched at full depth.
         bool doFullDepthSearch = true;
 
@@ -1177,19 +1181,24 @@ namespace {
             }
         }
 
-        if (doFullDepthSearch) // Go with full depth non-pv search
+        // Step 15. Full depth search
+        if (doFullDepthSearch)
         {
             ss[ply].reduction = Depth(0);
             value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
+
+            // Step extra. pv search (only in PV nodes)
             if (value > alpha && value < beta)
                 value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
         }
       }
+
+      // Step 16. Undo move
       pos.undo_move(move);
 
       assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
 
-      // New best move?
+      // Step 17. Check for new best move
       if (value > bestValue)
       {
           bestValue = value;
@@ -1202,7 +1211,7 @@ namespace {
           }
       }
 
-      // Split?
+      // Step 18. Check for split
       if (   TM.active_threads() > 1
           && bestValue < beta
           && depth >= MinimumSplitDepth
@@ -1215,11 +1224,13 @@ namespace {
           break;
     }
 
-    // All legal moves have been searched.  A special case: If there were
+    // Step 19. Check for mate and stalemate
+    // All legal moves have been searched and if there were
     // no legal moves, it must be mate or stalemate.
     if (moveCount == 0)
         return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
 
+    // Step 20. Update tables
     // If the search is not aborted, update the transposition table,
     // history counters, and killer moves.
     if (AbortSearch || TM.thread_should_stop(threadID))