Document why Book is defined static

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 4408475341ac9deea60df927609c4bfd61e79ae0..1f848183481a573cf59710f2993a1c4fb890a1f2 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -363,7 +363,7 @@ int64_t perft(Position& pos, Depth depth) {
 
 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
 
-  static Book book;
+  static Book book; // Define static to initialize the PRNG only once
 
   // Initialize global search-related variables
   StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = false;
@@ -780,8 +780,18 @@ namespace {
                                     : can_return_tt(tte, depth, beta, ss->ply)))
     {
         TT.refresh(tte);
-        ss->bestMove = ttMove; // Can be MOVE_NONE
-        return value_from_tt(tte->value(), ss->ply);
+        ss->bestMove = move = ttMove; // Can be MOVE_NONE
+        value = value_from_tt(tte->value(), ss->ply);
+
+        if (   value >= beta
+            && move
+            && !pos.move_is_capture_or_promotion(move)
+            && move != ss->killers[0])
+        {
+            ss->killers[1] = ss->killers[0];
+            ss->killers[0] = move;
+        }
+        return value;
     }
 
     // Step 5. Evaluate the position statically and update parent's gain statistics
@@ -1539,8 +1549,8 @@ split_point_start: // At split points actual search starts from here
     Piece p1, p2;
     Square ksq;
 
-    assert(m1 && move_is_ok(m1));
-    assert(m2 && move_is_ok(m2));
+    assert(move_is_ok(m1));
+    assert(move_is_ok(m2));
 
     // Case 1: The moving piece is the same in both moves
     f2 = move_from(m2);
@@ -1616,7 +1626,7 @@ split_point_start: // At split points actual search starts from here
   bool connected_threat(const Position& pos, Move m, Move threat) {
 
     assert(move_is_ok(m));
-    assert(threat && move_is_ok(threat));
+    assert(move_is_ok(threat));
     assert(!pos.move_is_capture_or_promotion(m));
     assert(!pos.move_is_passed_pawn_push(m));