X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=791cbc6fb580901a567296d23a0eeed08f892969;hp=eb19b51d9c994c5d11e8c9c7abfb195806e475af;hb=b366c7dc38145278a00c51a560a4f7b6e03a0b2a;hpb=2f6788104ffbc501a563344f65a1b6fba8e91bc5

diff --git a/src/search.cpp b/src/search.cpp
index eb19b51d..791cbc6f 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -297,6 +297,7 @@ namespace {
   Value value_to_tt(Value v, int ply);
   Value value_from_tt(Value v, int ply);
   bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
+  bool ok_to_use_TT_PV(const TTEntry* tte, Depth depth, Value alpha, Value beta, int ply);
   bool connected_threat(const Position& pos, Move m, Move threat);
   Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
   void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
@@ -838,14 +839,10 @@ namespace {
     tte = TT.retrieve(posKey);
     ttMove = tte ? tte->move() : MOVE_NONE;
 
-    // At PV nodes, we don't use the TT for pruning, but only for move ordering.
-    // This is to avoid problems in the following areas:
-    //
-    // * Repetition draw detection
-    // * Fifty move rule detection
-    // * Searching for a mate
-    // * Printing of full PV line
-    if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
+    // At PV nodes we check for exact scores within (alha, beta) range, while
+    // at non-PV nodes we check for and return a fail high/low. Biggest advantage
+    // at probing at PV nodes is to have a smooth experience in analysis mode.
+    if (!Root && tte && (PvNode ? ok_to_use_TT_PV(tte, depth, alpha, beta, ply) : ok_to_use_TT(tte, depth, beta, ply)))
     {
         TT.refresh(tte);
         ss->bestMove = ttMove; // Can be MOVE_NONE
@@ -1797,7 +1794,9 @@ split_point_start: // At split points actual search starts from here
 
 
   // ok_to_use_TT() returns true if a transposition table score
-  // can be used at a given point in search.
+  // can be used at a given point in search. There are two versions
+  // one to be used in non-PV nodes and one in PV nodes where we look
+  // for an exact score that falls between (alha, beta) boundaries.
 
   bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
 
@@ -1811,6 +1810,17 @@ split_point_start: // At split points actual search starts from here
               || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
   }
 
+  bool ok_to_use_TT_PV(const TTEntry* tte, Depth depth, Value alpha, Value beta, int ply) {
+
+    Value v = value_from_tt(tte->value(), ply);
+
+     return   tte->depth() >= depth
+           && tte->type() == VALUE_TYPE_EXACT
+           && tte->move() != MOVE_NONE
+           && v < beta
+           && v > alpha;
+  }
+
 
   // refine_eval() returns the transposition table score if
   // possible otherwise falls back on static position evaluation.