Add syzygy support

bench: 8080602

src/Makefile

@@ -36,7 +36,7 @@ PGOBENCH = ./$(EXE) bench 16 1 1000 default time
 ### Object files
 OBJS = benchmark.o bitbase.o bitboard.o endgame.o evaluate.o main.o \
 	material.o misc.o movegen.o movepick.o pawns.o position.o \
-	search.o thread.o timeman.o tt.o uci.o ucioption.o
+	search.o thread.o timeman.o tt.o uci.o ucioption.o syzygy/tbprobe.o
 
 ### ==========================================================================
 ### Section 2. High-level Configuration
@@ -375,14 +375,14 @@ profile-build:
 	$(MAKE) ARCH=$(ARCH) COMP=$(COMP) $(profile_prepare)
 	@echo ""
 	@echo "Step 1/4. Building executable for benchmark ..."
-	@touch *.cpp *.h
+	@touch *.cpp *.h syzygy/*.cpp syzygy/*.h
 	$(MAKE) ARCH=$(ARCH) COMP=$(COMP) $(profile_make)
 	@echo ""
 	@echo "Step 2/4. Running benchmark for pgo-build ..."
 	@$(PGOBENCH) > /dev/null
 	@echo ""
 	@echo "Step 3/4. Building final executable ..."
-	@touch *.cpp *.h
+	@touch *.cpp *.h syzygy/*.cpp syzygy/*.h
 	$(MAKE) ARCH=$(ARCH) COMP=$(COMP) $(profile_use)
 	@echo ""
 	@echo "Step 4/4. Deleting profile data ..."
@@ -397,7 +397,7 @@ install:
 	-strip $(BINDIR)/$(EXE)
 
 clean:
-	$(RM) $(EXE) $(EXE).exe *.o .depend *~ core bench.txt *.gcda
+	$(RM) $(EXE) $(EXE).exe *.o .depend *~ core bench.txt *.gcda ./syzygy/*.o ./syzygy/*.gcda
 
 default:
 	help
@@ -462,7 +462,7 @@ gcc-profile-use:
 	all
 
 gcc-profile-clean:
-	@rm -rf *.gcda *.gcno bench.txt
+	@rm -rf *.gcda *.gcno syzygy/*.gcda syzygy/*.gcno bench.txt
 
 icc-profile-prepare:
 	$(MAKE) ARCH=$(ARCH) COMP=$(COMP) icc-profile-clean

src/main.cpp

@@ -26,6 +26,7 @@
 #include "thread.h"
 #include "tt.h"
 #include "uci.h"
+#include "syzygy/tbprobe.h"
 
 int main(int argc, char* argv[]) {
 
@@ -39,6 +40,7 @@ int main(int argc, char* argv[]) {
   Eval::init();
   Pawns::init();
   Threads.init();
+  Tablebases::init(Options["SyzygyPath"]);
   TT.resize(Options["Hash"]);
 
   UCI::loop(argc, argv);

src/position.h

@@ -170,6 +170,7 @@ class Position {
   uint64_t nodes_searched() const;
   void set_nodes_searched(uint64_t n);
   bool is_draw() const;
+  int rule50_count() const;
   Score psq_score() const;
   Value non_pawn_material(Color c) const;
 
@@ -347,6 +348,10 @@ inline int Position::game_ply() const {
   return gamePly;
 }
 
+inline int Position::rule50_count() const {
+  return st->rule50;
+}
+
 inline uint64_t Position::nodes_searched() const {
   return nodes;
 }

src/search.cpp

@@ -33,6 +33,7 @@
 #include "thread.h"
 #include "tt.h"
 #include "uci.h"
+#include "syzygy/tbprobe.h"
 
 namespace Search {
 
@@ -44,6 +45,18 @@ namespace Search {
   StateStackPtr SetupStates;
 }
 
+namespace Tablebases {
+
+  int Cardinality;
+  uint64_t Hits;
+  bool RootInTB;
+  bool UseRule50;
+  Depth ProbeDepth;
+  Value Score;
+}
+
+namespace TB = Tablebases;
+
 using std::string;
 using Eval::evaluate;
 using namespace Search;
@@ -186,6 +199,19 @@ void Search::think() {
   DrawValue[ RootPos.side_to_move()] = VALUE_DRAW - Value(contempt);
   DrawValue[~RootPos.side_to_move()] = VALUE_DRAW + Value(contempt);
 
+  TB::Hits = 0;
+  TB::RootInTB = false;
+  TB::UseRule50 = Options["Syzygy50MoveRule"];
+  TB::ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
+  TB::Cardinality = Options["SyzygyProbeLimit"];
+
+  // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
+  if (TB::Cardinality > TB::MaxCardinality)
+  {
+      TB::Cardinality = TB::MaxCardinality;
+      TB::ProbeDepth = DEPTH_ZERO;
+  }
+
   if (RootMoves.empty())
   {
       RootMoves.push_back(MOVE_NONE);
@@ -195,6 +221,37 @@ void Search::think() {
   }
   else
   {
+      if (TB::Cardinality >=  RootPos.count<ALL_PIECES>(WHITE)
+                            + RootPos.count<ALL_PIECES>(BLACK))
+      {
+          // If the current root position is in the tablebases then RootMoves
+          // contains only moves that preserve the draw or win.
+          TB::RootInTB = Tablebases::root_probe(RootPos, RootMoves, TB::Score);
+
+          if (TB::RootInTB)
+              TB::Cardinality = 0; // Do not probe tablebases during the search
+
+          else // If DTZ tables are missing, use WDL tables as a fallback
+          {
+              // Filter out moves that do not preserve a draw or win
+              TB::RootInTB = Tablebases::root_probe_wdl(RootPos, RootMoves, TB::Score);
+
+              // Only probe during search if winning
+              if (TB::Score <= VALUE_DRAW)
+                  TB::Cardinality = 0;
+          }
+
+          if (TB::RootInTB)
+          {
+              TB::Hits = RootMoves.size();
+
+              if (!TB::UseRule50)
+                  TB::Score =  TB::Score > VALUE_DRAW ?  VALUE_MATE - MAX_PLY - 1
+                             : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1
+                                                      :  VALUE_DRAW;
+          }
+      }
+
       for (Thread* th : Threads)
           th->maxPly = 0;
 
@@ -487,6 +544,36 @@ namespace {
         return ttValue;
     }
 
+    // Step 4a. Tablebase probe
+    if (!RootNode && TB::Cardinality)
+    {
+        int piecesCnt = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
+
+        if (    piecesCnt <= TB::Cardinality
+            && (piecesCnt <  TB::Cardinality || depth >= TB::ProbeDepth)
+            &&  pos.rule50_count() == 0)
+        {
+            int found, v = Tablebases::probe_wdl(pos, &found);
+
+            if (found)
+            {
+                TB::Hits++;
+
+                int drawScore = TB::UseRule50 ? 1 : 0;
+
+                value =  v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
+                       : v >  drawScore ?  VALUE_MATE - MAX_PLY - ss->ply
+                                        :  VALUE_DRAW + 2 * v * drawScore;
+
+                tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
+                          std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
+                          MOVE_NONE, VALUE_NONE, TT.generation());
+
+                return value;
+            }
+        }
+    }
+
     // Step 5. Evaluate the position statically and update parent's gain statistics
     if (inCheck)
     {
@@ -1347,6 +1434,9 @@ namespace {
         Depth d = updated ? depth : depth - ONE_PLY;
         Value v = updated ? RootMoves[i].score : RootMoves[i].previousScore;
 
+        bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
+        v = tb ? TB::Score : v;
+
         if (ss.rdbuf()->in_avail()) // Not at first line
             ss << "\n";
 
@@ -1355,11 +1445,12 @@ namespace {
            << " multipv "   << i + 1
            << " score "     << UCI::value(v);
 
-        if (i == PVIdx)
+        if (!tb && i == PVIdx)
               ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
 
         ss << " nodes "     << pos.nodes_searched()
            << " nps "       << pos.nodes_searched() * 1000 / elapsed
+           << " tbhits "    << TB::Hits
            << " time "      << elapsed
            << " pv";
 

src/thread.h

@@ -37,8 +37,6 @@ struct Thread;
 const int MAX_THREADS = 128;
 const int MAX_SPLITPOINTS_PER_THREAD = 8;
 
-struct Thread;
-
 /// SplitPoint struct stores information shared by the threads searching in
 /// parallel below the same split point. It is populated at splitting time.
 

src/types.h

@@ -184,8 +184,8 @@ enum Value : int {
   VALUE_INFINITE  = 32001,
   VALUE_NONE      = 32002,
 
-  VALUE_MATE_IN_MAX_PLY  =  VALUE_MATE - MAX_PLY,
-  VALUE_MATED_IN_MAX_PLY = -VALUE_MATE + MAX_PLY,
+  VALUE_MATE_IN_MAX_PLY  =  VALUE_MATE - 2 * MAX_PLY,
+  VALUE_MATED_IN_MAX_PLY = -VALUE_MATE + 2 * MAX_PLY,
 
   PawnValueMg   = 198,   PawnValueEg   = 258,
   KnightValueMg = 817,   KnightValueEg = 846,

src/uci.cpp

@@ -220,7 +220,7 @@ string UCI::value(Value v) {
 
   stringstream ss;
 
-  if (abs(v) < VALUE_MATE_IN_MAX_PLY)
+  if (abs(v) < VALUE_MATE - MAX_PLY)
       ss << "cp " << v * 100 / PawnValueEg;
   else
       ss << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;

src/ucioption.cpp

@@ -25,6 +25,7 @@
 #include "thread.h"
 #include "tt.h"
 #include "uci.h"
+#include "syzygy/tbprobe.h"
 
 using std::string;
 
@@ -37,6 +38,7 @@ void on_clear_hash(const Option&) { TT.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(); }
+void on_tb_path(const Option& o) { Tablebases::init(o); }
 
 
 /// Our case insensitive less() function as required by UCI protocol
@@ -66,6 +68,10 @@ void init(OptionsMap& o) {
   o["Minimum Thinking Time"] << Option(20, 0, 5000);
   o["Slow Mover"]            << Option(80, 10, 1000);
   o["UCI_Chess960"]          << Option(false);
+  o["SyzygyPath"]            << Option("<empty>", on_tb_path);
+  o["SyzygyProbeDepth"]      << Option(1, 1, 100);
+  o["Syzygy50MoveRule"]      << Option(true);
+  o["SyzygyProbeLimit"]      << Option(6, 0, 6);
 }