Simplify verification search (#1362)

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 4ad1eebbf6a6fed3af64640855ed2a715684f0b3..2fd842070cfe2720217eb6f8876aa02ba61075a7 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -2,7 +2,7 @@
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
   Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
-  Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+  Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -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);
 
@@ -175,13 +173,7 @@ void Search::clear() {
 
   Time.availableNodes = 0;
   TT.clear();
-
-  for (Thread* th : Threads)
-      th->clear();
-
-  Threads.main()->callsCnt = 0;
-  Threads.main()->previousScore = VALUE_INFINITE;
-  Threads.main()->previousTimeReduction = 1;
+  Threads.clear();
 }
 
 
@@ -202,8 +194,9 @@ 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 +437,7 @@ 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 +525,7 @@ 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
@@ -559,7 +551,7 @@ namespace {
     // search to overwrite a previous full search TT value, so we use a different
     // position key in case of an excluded move.
     excludedMove = ss->excludedMove;
-    posKey = pos.key() ^ Key(excludedMove);
+    posKey = pos.key() ^ Key(excludedMove << 16); // isn't a very good hash
     tte = TT.probe(posKey, ttHit);
     ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
     ttMove =  rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
@@ -683,7 +675,8 @@ 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->nmp_odd))
     {
 
         assert(eval - beta >= 0);
@@ -705,13 +698,19 @@ namespace {
             if (nullValue >= VALUE_MATE_IN_MAX_PLY)
                 nullValue = beta;
 
-            if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
+            if (abs(beta) < VALUE_KNOWN_WIN && (depth < 12 * ONE_PLY || thisThread->nmp_ply))
                 return nullValue;
 
             // Do verification search at high depths
+            // disable null move pruning for side to move for the first part of the remaining search tree
+            thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4;
+            thisThread->nmp_odd = ss->ply % 2;
+
             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->nmp_odd = thisThread->nmp_ply = 0;
+
             if (v >= beta)
                 return nullValue;
         }
@@ -1074,7 +1073,7 @@ 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 +1141,7 @@ 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);
 
@@ -1496,7 +1494,7 @@ moves_loop: // When in check search starts from here
     if (Threads.ponder)
         return;
 
-    if (   (Limits.use_time_management() && elapsed > Time.maximum())
+    if (   (Limits.use_time_management() && elapsed > Time.maximum() - 10)
         || (Limits.movetime && elapsed >= Limits.movetime)
         || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
             Threads.stop = true;