Assorted trivia in search.cpp

The only interesting change is the moving of
stack[MAX_PLY+4] back to its original position
in id_loop (now renamed Thread::search).

No functional change.

src/benchmark.cpp

@@ -91,8 +91,8 @@ const vector<string> Defaults = {
 void benchmark(const Position& current, istream& is) {
 
   string token;
-  Search::LimitsType limits;
   vector<string> fens;
+  Search::LimitsType limits;
 
   // Assign default values to missing arguments
   string ttSize    = (is >> token) ? token : "16";
@@ -103,10 +103,10 @@ void benchmark(const Position& current, istream& is) {
 
   Options["Hash"]    = ttSize;
   Options["Threads"] = threads;
-  Search::reset();
+  Search::clear();
 
   if (limitType == "time")
-      limits.movetime = stoi(limit); // movetime is in ms
+      limits.movetime = stoi(limit); // movetime is in millisecs
 
   else if (limitType == "nodes")
       limits.nodes = stoi(limit);
@@ -151,7 +151,7 @@ void benchmark(const Position& current, istream& is) {
       cerr << "\nPosition: " << i + 1 << '/' << fens.size() << endl;
 
       if (limitType == "perft")
-          nodes += Search::perft<true>(pos, limits.depth * ONE_PLY);
+          nodes += Search::perft(pos, limits.depth * ONE_PLY);
 
       else
       {

src/endgame.cpp

@@ -60,7 +60,7 @@ namespace {
   const int PushAway [8] = { 0, 5, 20, 40, 60, 80, 90, 100 };
 
   // Pawn Rank based scaling factors used in KRPPKRP endgame
-  const int KRPPKRPScaleFactors[RANK_NB] = {0, 9, 10, 14, 21, 44, 0, 0};
+  const int KRPPKRPScaleFactors[RANK_NB] = { 0, 9, 10, 14, 21, 44, 0, 0 };
 
 #ifndef NDEBUG
   bool verify_material(const Position& pos, Color c, Value npm, int pawnsCnt) {

src/search.cpp

@@ -174,9 +174,9 @@ void Search::init() {
 }
 
 
-/// Search::reset() clears all search memory, to obtain reproducible search results
+/// Search::clear() resets to zero search state, to obtain reproducible results
 
-void Search::reset () {
+void Search::clear() {
 
   TT.clear();
   CounterMovesHistory.clear();
@@ -216,7 +216,7 @@ uint64_t Search::perft(Position& pos, Depth depth) {
   return nodes;
 }
 
-template uint64_t Search::perft<true>(Position& pos, Depth depth);
+template uint64_t Search::perft<true>(Position&, Depth);
 
 
 /// MainThread::think() is called by the main thread when the program receives
@@ -344,7 +344,7 @@ void MainThread::think() {
 
 void Thread::search(bool isMainThread) {
 
-  Stack* ss = stack + 2; // To allow referencing (ss-2) and (ss+2)
+  Stack stack[MAX_PLY+4], *ss = stack+2; // To allow referencing (ss-2) and (ss+2)
   Value bestValue, alpha, beta, delta;
   Move easyMove = MOVE_NONE;
 
@@ -836,7 +836,7 @@ moves_loop: // When in check search starts from here
 
       if (RootNode && thisThread == Threads.main())
       {
-          Signals.firstRootMove = moveCount == 1;
+          Signals.firstRootMove = (moveCount == 1);
 
           if (Time.elapsed() > 3000)
               sync_cout << "info depth " << depth / ONE_PLY
@@ -1095,7 +1095,7 @@ moves_loop: // When in check search starts from here
              && is_ok((ss - 1)->currentMove)
              && is_ok((ss - 2)->currentMove))
     {
-        Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY -1);
+        Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
         Square prevPrevSq = to_sq((ss - 2)->currentMove);
         CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
         prevCmh.update(pos.piece_on(prevSq), prevSq, bonus);
@@ -1359,8 +1359,8 @@ moves_loop: // When in check search starts from here
   }
 
 
-  // update_stats() updates killers, history, countermove history and
+  // update_stats() updates killers, history, countermove and countermove
-  // countermoves stats for a quiet best move.
+  // history when a new quiet best move is found.
 
   void update_stats(const Position& pos, Stack* ss, Move move,
                     Depth depth, Move* quiets, int quietsCnt) {
@@ -1371,7 +1371,7 @@ moves_loop: // When in check search starts from here
         ss->killers[0] = move;
     }
 
-    Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY -1);
+    Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
 
     Square prevSq = to_sq((ss-1)->currentMove);
     CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
@@ -1394,14 +1394,14 @@ moves_loop: // When in check search starts from here
             cmh.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
     }
 
-    // Extra penalty for TT move in previous ply when it gets refuted
+    // Extra penalty for a quiet TT move in previous ply when it gets refuted
     if (   (ss-1)->moveCount == 1
         && !pos.captured_piece_type()
         && is_ok((ss-2)->currentMove))
     {
         Square prevPrevSq = to_sq((ss-2)->currentMove);
         CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
-        prevCmh.update(pos.piece_on(prevSq), prevSq, -bonus - 2 * ((depth + 1) / ONE_PLY));
+        prevCmh.update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY);
     }
   }
 
@@ -1411,23 +1411,23 @@ moves_loop: // When in check search starts from here
 
   Move Skill::pick_best(size_t multiPV) {
 
-    // PRNG sequence should be non-deterministic, so we seed it with the time at init
     const Search::RootMoveVector& rootMoves = Threads.main()->rootMoves;
-    static PRNG rng(now());
+    static PRNG rng(now()); // PRNG sequence should be non-deterministic
 
     // RootMoves are already sorted by score in descending order
-    int variance = std::min(rootMoves[0].score - rootMoves[multiPV - 1].score, PawnValueMg);
+    Value topScore = rootMoves[0].score;
+    int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
     int weakness = 120 - 2 * level;
     int maxScore = -VALUE_INFINITE;
 
-    // Choose best move. For each move score we add two terms both dependent on
+    // Choose best move. For each move score we add two terms, both dependent on
     // weakness. One deterministic and bigger for weaker levels, and one random,
     // then we choose the move with the resulting highest score.
     for (size_t i = 0; i < multiPV; ++i)
     {
         // This is our magic formula
-        int push = (  weakness * int(rootMoves[0].score - rootMoves[i].score)
+        int push = (  weakness * int(topScore - rootMoves[i].score)
-                    + variance * (rng.rand<unsigned>() % weakness)) / 128;
+                    + delta * (rng.rand<unsigned>() % weakness)) / 128;
 
         if (rootMoves[i].score + push > maxScore)
         {
@@ -1435,6 +1435,7 @@ moves_loop: // When in check search starts from here
             best = rootMoves[i].pv[0];
         }
     }
+
     return best;
   }
 
@@ -1512,7 +1513,8 @@ void RootMove::insert_pv_in_tt(Position& pos) {
       TTEntry* tte = TT.probe(pos.key(), ttHit);
 
       if (!ttHit || tte->move() != m) // Don't overwrite correct entries
-          tte->save(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, m, VALUE_NONE, TT.generation());
+          tte->save(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE,
+                    m, VALUE_NONE, TT.generation());
 
       pos.do_move(m, *st++, pos.gives_check(m, CheckInfo(pos)));
   }
@@ -1522,10 +1524,10 @@ void RootMove::insert_pv_in_tt(Position& pos) {
 }
 
 
-/// RootMove::extract_ponder_from_tt() is called in case we have no ponder move before
+/// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
-/// exiting the search, for instance in case we stop the search during a fail high at
+/// before exiting the search, for instance in case we stop the search during a
-/// root. We try hard to have a ponder move to return to the GUI, otherwise in case of
+/// fail high at root. We try hard to have a ponder move to return to the GUI,
-/// 'ponder on' we have nothing to think on.
+/// otherwise in case of 'ponder on' we have nothing to think on.
 
 bool RootMove::extract_ponder_from_tt(Position& pos)
 {
@@ -1549,11 +1551,11 @@ bool RootMove::extract_ponder_from_tt(Position& pos)
 }
 
 
-/// check_time() is called by the timer thread when the timer triggers. It is
+/// TimerThread::check_time() is called by when the timer triggers. It is used
-/// used to print debug info and, more importantly, to detect when we are out of
+/// to print debug info and, more importantly, to detect when we are out of
 /// available time and thus stop the search.
 
-void check_time() {
+void TimerThread::check_time() {
 
   static TimePoint lastInfoTime = now();
   int elapsed = Time.elapsed();

src/search.h

@@ -103,8 +103,8 @@ extern LimitsType Limits;
 extern StateStackPtr SetupStates;
 
 void init();
-void reset();
+void clear();
-template<bool Root> uint64_t perft(Position& pos, Depth depth);
+template<bool Root = true> uint64_t perft(Position& pos, Depth depth);
 
 } // namespace Search
 

src/thread.cpp

@@ -29,8 +29,6 @@ using namespace Search;
 
 ThreadPool Threads; // Global object
 
-extern void check_time();
-
 namespace {
 
  // Helpers to launch a thread after creation and joining before delete. Outside the

src/thread.h

@@ -34,10 +34,6 @@
 #include "search.h"
 #include "thread_win32.h"
 
-struct Thread;
-
-const size_t MAX_THREADS = 128;
-
 
 /// ThreadBase struct is the base of the hierarchy from where we derive all the
 /// specialized thread classes.
@@ -78,7 +74,6 @@ struct Thread : public ThreadBase {
   Position rootPos;
   Search::RootMoveVector rootMoves;
   Depth rootDepth;
-  Search::Stack stack[MAX_PLY+4];
   HistoryStats history;
   MovesStats counterMoves;
 };
@@ -100,6 +95,7 @@ struct TimerThread : public ThreadBase {
   static const int Resolution = 5; // Millisec between two check_time() calls
 
   virtual void idle_loop();
+  void check_time();
 
   bool run = false;
 };

src/uci.cpp

@@ -182,7 +182,7 @@ void UCI::loop(int argc, char* argv[]) {
 
       else if (token == "ucinewgame")
       {
-          Search::reset();
+          Search::clear();
           Time.availableNodes = 0;
       }
       else if (token == "isready")    sync_cout << "readyok" << sync_endl;

src/ucioption.cpp

@@ -35,7 +35,7 @@ UCI::OptionsMap Options; // Global object
 namespace UCI {
 
 /// 'On change' actions, triggered by an option's value change
-void on_clear_hash(const Option&) { Search::reset(); }
+void on_clear_hash(const Option&) { Search::clear(); }
 void on_hash_size(const Option& o) { TT.resize(o); }
 void on_logger(const Option& o) { start_logger(o); }
 void on_threads(const Option&) { Threads.read_uci_options(); }
@@ -58,7 +58,7 @@ void init(OptionsMap& o) {
 
   o["Write Debug Log"]       << Option(false, on_logger);
   o["Contempt"]              << Option(0, -100, 100);
-  o["Threads"]               << Option(1, 1, MAX_THREADS, on_threads);
+  o["Threads"]               << Option(1, 1, 128, on_threads);
   o["Hash"]                  << Option(16, 1, MaxHashMB, on_hash_size);
   o["Clear Hash"]            << Option(on_clear_hash);
   o["Ponder"]                << Option(true);