Enhanced verify search (#1338)

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 4ad1eebbf6a6fed3af64640855ed2a715684f0b3..8b3b8fb4864436c17c6964a24151a85db92f873f 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -96,8 +96,6 @@ namespace {
     Move best = MOVE_NONE;
   };
 
-  Value DrawValue[COLOR_NB];
-
   template <NodeType NT>
   Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning);
 
@@ -202,8 +200,9 @@ void MainThread::search() {
   TT.new_search();
 
   int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
-  DrawValue[ us] = VALUE_DRAW - Value(contempt);
-  DrawValue[~us] = VALUE_DRAW + Value(contempt);
+
+  Eval::Contempt = (us == WHITE ?  make_score(contempt, contempt / 2)
+                                : -make_score(contempt, contempt / 2));
 
   if (rootMoves.empty())
   {
@@ -444,7 +443,7 @@ void Thread::search() {
               int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
 
               Color us = rootPos.side_to_move();
-              bool thinkHard =    DrawValue[us] == bestValue
+              bool thinkHard =    bestValue == VALUE_DRAW
                                && Limits.time[us] - Time.elapsed() > Limits.time[~us]
                                && ::pv_is_draw(rootPos);
 
@@ -532,8 +531,7 @@ namespace {
     {
         // Step 2. Check for aborted search and immediate draw
         if (Threads.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
-            return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
-                                                  : DrawValue[pos.side_to_move()];
+            return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos) : VALUE_DRAW;
 
         // Step 3. Mate distance pruning. Even if we mate at the next move our score
         // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
@@ -683,7 +681,8 @@ namespace {
     // Step 8. Null move search with verification search (is omitted in PV nodes)
     if (   !PvNode
         &&  eval >= beta
-        &&  ss->staticEval >= beta - 36 * depth / ONE_PLY + 225)
+        &&  ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
+               && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 == thisThread->pair))
     {
 
         assert(eval - beta >= 0);
@@ -709,8 +708,17 @@ namespace {
                 return nullValue;
 
             // Do verification search at high depths
+            R += ONE_PLY;
+            // disable null move pruning for side to move for the first part of the remaining search tree
+            int nmp_ply = thisThread->nmp_ply;
+            int pair = thisThread->pair;
+            thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4;
+            thisThread->pair = (ss->ply % 2) == 0;
+
             Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta)
                                         :  search<NonPV>(pos, ss, beta-1, beta, depth-R, false, true);
+            thisThread->pair = pair;
+            thisThread->nmp_ply = nmp_ply;
 
             if (v >= beta)
                 return nullValue;
@@ -1074,7 +1082,7 @@ moves_loop: // When in check search starts from here
 
     if (!moveCount)
         bestValue = excludedMove ? alpha
-                   :     inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
+                   :     inCheck ? mated_in(ss->ply) : VALUE_DRAW;
     else if (bestMove)
     {
         // Quiet best move: update move sorting heuristics
@@ -1142,8 +1150,7 @@ moves_loop: // When in check search starts from here
 
     // Check for an instant draw or if the maximum ply has been reached
     if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
-        return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
-                                              : DrawValue[pos.side_to_move()];
+        return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos) : VALUE_DRAW;
 
     assert(0 <= ss->ply && ss->ply < MAX_PLY);