Use less time on recaptures, credit to peregrine in Discord.

Bench 1836777

src/engine.cpp

@@ -97,11 +97,12 @@ void Engine::set_on_bestmove(std::function<void(std::string_view, std::string_vi
 
 void Engine::wait_for_search_finished() { threads.main_thread()->wait_for_search_finished(); }
 
-void Engine::set_position(const std::string& fen, const std::vector<std::string>& moves) {
+Square Engine::set_position(const std::string& fen, const std::vector<std::string>& moves) {
     // Drop the old state and create a new one
     states = StateListPtr(new std::deque<StateInfo>(1));
     pos.set(fen, options["UCI_Chess960"], &states->back());
 
+    Square capSq = SQ_NONE;
     for (const auto& move : moves)
     {
         auto m = UCIEngine::to_move(pos, move);
@@ -111,7 +112,13 @@ void Engine::set_position(const std::string& fen, const std::vector<std::string>
 
         states->emplace_back();
         pos.do_move(m, states->back());
+
+        capSq          = SQ_NONE;
+        DirtyPiece& dp = states->back().dirtyPiece;
+        if (dp.dirty_num > 1 && dp.to[1] == SQ_NONE)
+            capSq = m.to_sq();
     }
+    return capSq;
 }
 
 // modifiers
@@ -172,4 +179,4 @@ std::string Engine::visualize() const {
     return ss.str();
 }
 
-}
+}

src/engine.h

@@ -57,7 +57,8 @@ class Engine {
     // blocking call to wait for search to finish
     void wait_for_search_finished();
     // set a new position, moves are in UCI format
-    void set_position(const std::string& fen, const std::vector<std::string>& moves);
+    // If last of moves is a capture, the capture square is returned
+    Square set_position(const std::string& fen, const std::vector<std::string>& moves);
 
     // modifiers
 
@@ -104,4 +105,4 @@ class Engine {
 }  // namespace Stockfish
 
 
-#endif  // #ifndef ENGINE_H_INCLUDED
+#endif  // #ifndef ENGINE_H_INCLUDED

src/search.cpp

@@ -446,9 +446,11 @@ void Search::Worker::iterative_deepening() {
             double reduction = (1.48 + mainThread->previousTimeReduction) / (2.17 * timeReduction);
             double bestMoveInstability = 1 + 1.88 * totBestMoveChanges / threads.size();
             int    el                  = std::clamp((bestValue + 750) / 150, 0, 9);
+            double recapture =
+              limits.capSq != SQ_NONE && limits.capSq == rootMoves[0].pv[0].to_sq() ? 0.898 : 0.945;
 
             double totalTime = mainThread->tm.optimum() * fallingEval * reduction
-                             * bestMoveInstability * EvalLevel[el];
+                             * bestMoveInstability * EvalLevel[el] * recapture;
 
             // Cap used time in case of a single legal move for a better viewer experience
             if (rootMoves.size() == 1)

src/search.h

@@ -128,6 +128,7 @@ struct LimitsType {
     int                      movestogo, depth, mate, perft, infinite;
     uint64_t                 nodes;
     bool                     ponderMode;
+    Square                   capSq;
 };
 
 

src/uci.cpp

@@ -97,6 +97,7 @@ UCIEngine::UCIEngine(int argc, char** argv) :
 void UCIEngine::loop() {
 
     std::string token, cmd;
+    Square      capSq = SQ_NONE;
 
     for (int i = 1; i < cli.argc; ++i)
         cmd += std::string(cli.argv[i]) + " ";
@@ -129,9 +130,9 @@ void UCIEngine::loop() {
         else if (token == "setoption")
             setoption(is);
         else if (token == "go")
-            go(is);
+            go(is, capSq);
         else if (token == "position")
-            position(is);
+            capSq = position(is);
         else if (token == "ucinewgame")
             engine.search_clear();
         else if (token == "isready")
@@ -177,11 +178,12 @@ void UCIEngine::loop() {
     } while (token != "quit" && cli.argc == 1);  // The command-line arguments are one-shot
 }
 
-Search::LimitsType UCIEngine::parse_limits(std::istream& is) {
+Search::LimitsType UCIEngine::parse_limits(std::istream& is, Square capSq) {
     Search::LimitsType limits;
     std::string        token;
 
     limits.startTime = now();  // The search starts as early as possible
+    limits.capSq     = capSq;
 
     while (is >> token)
         if (token == "searchmoves")  // Needs to be the last command on the line
@@ -216,9 +218,9 @@ Search::LimitsType UCIEngine::parse_limits(std::istream& is) {
     return limits;
 }
 
-void UCIEngine::go(std::istringstream& is) {
+void UCIEngine::go(std::istringstream& is, Square capSq) {
 
-    Search::LimitsType limits = parse_limits(is);
+    Search::LimitsType limits = parse_limits(is, capSq);
 
     if (limits.perft)
         perft(limits);
@@ -255,7 +257,7 @@ void UCIEngine::bench(std::istream& args) {
                       << std::endl;
             if (token == "go")
             {
-                Search::LimitsType limits = parse_limits(is);
+                Search::LimitsType limits = parse_limits(is, SQ_NONE);
 
                 if (limits.perft)
                     nodes = perft(limits);
@@ -306,7 +308,7 @@ std::uint64_t UCIEngine::perft(const Search::LimitsType& limits) {
     return nodes;
 }
 
-void UCIEngine::position(std::istringstream& is) {
+Square UCIEngine::position(std::istringstream& is) {
     std::string token, fen;
 
     is >> token;
@@ -320,7 +322,7 @@ void UCIEngine::position(std::istringstream& is) {
         while (is >> token && token != "moves")
             fen += token + " ";
     else
-        return;
+        return SQ_NONE;
 
     std::vector<std::string> moves;
 
@@ -329,7 +331,7 @@ void UCIEngine::position(std::istringstream& is) {
         moves.push_back(token);
     }
 
-    engine.set_position(fen, moves);
+    return engine.set_position(fen, moves);
 }
 
 namespace {

src/uci.h

@@ -50,18 +50,18 @@ class UCIEngine {
     static std::string to_lower(std::string str);
     static Move        to_move(const Position& pos, std::string str);
 
-    static Search::LimitsType parse_limits(std::istream& is);
+    static Search::LimitsType parse_limits(std::istream& is, Square capSq);
 
     auto& engine_options() { return engine.get_options(); }
 
    private:
     Engine      engine;
     CommandLine cli;
 
-    void          go(std::istringstream& is);
+    void          go(std::istringstream& is, Square capSq);
     void          bench(std::istream& args);
-    void          position(std::istringstream& is);
     void          setoption(std::istringstream& is);
+    Square        position(std::istringstream& is);
     std::uint64_t perft(const Search::LimitsType&);
 
     static void on_update_no_moves(const Engine::InfoShort& info);