Use null move when depth >= 2 plies

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 72abae26a9d286f829fdfc9f2ac7053b14525cd2..9ae28d3c55870b554a5681782442dbbc3569b3c3 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -303,7 +303,7 @@ namespace {
 
   void id_loop(Position& pos) {
 
-    Stack stack[MAX_PLY_PLUS_3], *ss = stack+2; // To allow referencing (ss-2)
+    Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
     int depth, prevBestMoveChanges;
     Value bestValue, alpha, beta, delta;
 
@@ -663,7 +663,7 @@ namespace {
     // Step 8. Null move search with verification search (is omitted in PV nodes)
     if (   !PvNode
         && !ss->skipNullMove
-        &&  depth > ONE_PLY
+        &&  depth >= 2 * ONE_PLY
         &&  eval >= beta
         &&  abs(beta) < VALUE_MATE_IN_MAX_PLY
         &&  pos.non_pawn_material(pos.side_to_move()))
@@ -1575,7 +1575,7 @@ moves_loop: // When in check and at SpNode search starts from here
 
 void RootMove::extract_pv_from_tt(Position& pos) {
 
-  StateInfo state[MAX_PLY_PLUS_3], *st = state;
+  StateInfo state[MAX_PLY_PLUS_6], *st = state;
   const TTEntry* tte;
   int ply = 0;
   Move m = pv[0];
@@ -1608,7 +1608,7 @@ void RootMove::extract_pv_from_tt(Position& pos) {
 
 void RootMove::insert_pv_in_tt(Position& pos) {
 
-  StateInfo state[MAX_PLY_PLUS_3], *st = state;
+  StateInfo state[MAX_PLY_PLUS_6], *st = state;
   const TTEntry* tte;
   int ply = 0;
 
@@ -1683,7 +1683,7 @@ void Thread::idle_loop() {
 
           Threads.mutex.unlock();
 
-          Stack stack[MAX_PLY_PLUS_3], *ss = stack+2; // To allow referencing (ss-2)
+          Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
           Position pos(*sp->pos, this);
 
           std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));