Stockfish 1.1a

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/benchmark.cpp

@@ -71,8 +71,8 @@ void benchmark(const std::string& commandLine) {
 
   std::istringstream csVal(commandLine);
   std::istringstream csStr(commandLine);
-  std::string ttSize, threads, fileName;
-  int val, secsPerPos;
+  std::string ttSize, threads, fileName, limitType;
+  int val, secsPerPos, maxDepth, maxNodes;
 
   csStr >> ttSize;
   csVal >> val;
@@ -95,8 +95,18 @@ void benchmark(const std::string& commandLine) {
   set_option_value("Use Search Log", "true");
   set_option_value("Search Log Filename", "bench.txt");
 
-  csVal >> secsPerPos;
+  csVal >> val;
   csVal >> fileName;
+  csVal >> limitType;
+
+  secsPerPos = maxDepth = maxNodes = 0;
+
+  if (limitType == "time")
+      secsPerPos = val * 1000;
+  else if (limitType == "depth")
+      maxDepth = val;
+  else
+      maxNodes = val;
 
   std::vector<std::string> positions;
   
@@ -121,12 +131,21 @@ void benchmark(const std::string& commandLine) {
       for (int i = 0; i < 16; i++)
           positions.push_back(std::string(BenchmarkPositions[i]));
 
+  int startTime = get_system_time();
   std::vector<std::string>::iterator it;
-  for (it = positions.begin(); it != positions.end(); ++it)
+  int cnt = 1;
+  int64_t totalNodes = 0;
+  for (it = positions.begin(); it != positions.end(); ++it, ++cnt)
   {
-      Move moves[1] = {MOVE_NONE};
-      int dummy[2] = {0, 0};
+      Move moves[1] = {MOVE_NONE};
+      int dummy[2] = {0, 0};
       Position pos(*it);
-      think(pos, true, false, 0, dummy, dummy, 0, 0, 0, secsPerPos * 1000, moves);
+      std::cout << "\nProcessing position " << cnt << '/' << positions.size() << std::endl << std::endl;
+      think(pos, true, false, 0, dummy, dummy, 0, maxDepth, maxNodes, secsPerPos, moves);
+      totalNodes += nodes_searched();
   }
+  std::cout << "\nProcessing time (ms) " << get_system_time() - startTime << std::endl
+            << "Nodes searched " << totalNodes << std::endl
+            << "Press any key to exit" << std::endl;
+  std::cin >> fileName;
 }

src/evaluate.cpp

@@ -1120,13 +1120,7 @@ namespace {
 
     ev = apply_scale_factor(ev, sf[(ev > Value(0) ? WHITE : BLACK)]);
 
-    // Linearized sigmoid interpolator
-    int sph = int(ph);
-    sph -= (64 - sph) / 4;
-    sph = Min(PHASE_MIDGAME, Max(PHASE_ENDGAME, sph));
-
-    Value result = Value(int((mv * sph + ev * (128 - sph)) / 128));
-
+    Value result = Value(int((mv * ph + ev * (128 - ph)) / 128));
     return Value(int(result) & ~(GrainSize - 1));
   }
 

src/history.cpp

@@ -23,6 +23,7 @@
 ////
 
 #include <cassert>
+#include <cstring>
 
 #include "history.h"
 

src/main.cpp

@@ -71,16 +71,18 @@ int main(int argc, char *argv[]) {
   // Process command line arguments
   if (argc >= 2 && string(argv[1]) == "bench")
   {
-      if (argc < 4 || argc > 6)
+      if (argc < 4 || argc > 7)
       {
         std::cout << "Usage: glaurung bench <hash size> <threads> "
-                  << "[time = 60s] [fen positions file = default]"
+                  << "[time = 60s] [fen positions file = default] "
+                  << "[time, depth or node limited = time]"
                   << std::endl;
         exit(0);
       }
       string time = argc > 4 ? argv[4] : "60";
       string fen = argc > 5 ? argv[5] : "default";
-      benchmark(string(argv[2]) + " " + string(argv[3]) + " " + time + " " + fen);
+      string lim = argc > 6 ? argv[6] : "time";
+      benchmark(string(argv[2]) + " " + string(argv[3]) + " " + time + " " + fen + " " + lim);
       return 0;
   }
 

src/material.cpp

@@ -23,6 +23,7 @@
 ////
 
 #include <cassert>
+#include <cstring>
 #include <map>
 
 #include "material.h"

src/misc.h

@@ -37,7 +37,7 @@
 /// Version number.  If this is left empty, the current date (in the format
 /// YYMMDD) is used as a version number.
 
-const std::string EngineVersion = "1.0";
+const std::string EngineVersion = "1.1a";
 
 
 ////
@@ -60,21 +60,21 @@ extern int Bioskey();
 ////
 //// Debug
 ////
+extern bool dbg_show_mean;
+extern bool dbg_show_hit_rate;
+
 extern long dbg_cnt0;
 extern long dbg_cnt1;
 
-inline void dbg_hit_on(bool b) { dbg_cnt0++; if (b) dbg_cnt1++; }
+inline void dbg_hit_on(bool b) { dbg_show_hit_rate = true; dbg_cnt0++; if (b) dbg_cnt1++; }
 inline void dbg_hit_on_c(bool c, bool b) { if (c) dbg_hit_on(b); }
 
-inline void dbg_before() { dbg_cnt0++; }
-inline void dbg_after() { dbg_cnt1++; }
+inline void dbg_before() { dbg_show_hit_rate = true; dbg_cnt0++; }
+inline void dbg_after() { dbg_show_hit_rate = true; dbg_cnt1++; }
 
 inline void dbg_mean_of(int v) { dbg_cnt0++; dbg_cnt1 += v; }
 
 extern void dbg_print_hit_rate();
 extern void dbg_print_mean();
 
-extern bool dbg_show_mean;
-extern bool dbg_show_hit_rate;
-
 #endif // !defined(MISC_H_INCLUDED)

src/movegen.cpp

@@ -122,15 +122,16 @@ int generate_captures(const Position& pos, MoveStack* mlist) {
   Bitboard target = pos.pieces_of_color(opposite_color(us));
   MoveStack* mlist_start = mlist;
 
+  mlist = generate_piece_moves<QUEEN>(pos, mlist, us, target);
+  mlist = generate_piece_moves<ROOK>(pos, mlist, us, target);
+  mlist = generate_piece_moves<BISHOP>(pos, mlist, us, target);
+  mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, target);
+
   if (us == WHITE)
       mlist = generate_pawn_captures<WHITE>(pos, mlist);
   else
       mlist = generate_pawn_captures<BLACK>(pos, mlist);
 
-  mlist = generate_piece_moves<KNIGHT>(pos, mlist, us, target);
-  mlist = generate_piece_moves<BISHOP>(pos, mlist, us, target);
-  mlist = generate_piece_moves<ROOK>(pos, mlist, us, target);
-  mlist = generate_piece_moves<QUEEN>(pos, mlist, us, target);
   mlist = generate_piece_moves<KING>(pos, mlist, us, target);
   return int(mlist - mlist_start);
 }

src/movepick.cpp

@@ -26,6 +26,7 @@
 #include <cassert>
 
 #include "history.h"
+#include "evaluate.h"
 #include "movegen.h"
 #include "movepick.h"
 #include "search.h"
@@ -44,7 +45,9 @@ namespace {
   int MainSearchPhaseIndex;
   int EvasionsPhaseIndex;
   int QsearchWithChecksPhaseIndex;
+  int QsearchNoCapturesPhaseIndex;
   int QsearchWithoutChecksPhaseIndex;
+  int NoMovesPhaseIndex;
 
 }
 
@@ -62,28 +65,38 @@ namespace {
 /// search captures, promotions and some checks) and about how important good
 /// move ordering is at the current node.
 
-MovePicker::MovePicker(const Position& p, bool pvnode, Move ttm, Move mk,
-                       Move k1, Move k2, Depth d) : pos(p) {
-  pvNode = pvnode;
+MovePicker::MovePicker(const Position& p, bool pv, Move ttm,
+                       const SearchStack& ss, Depth d, EvalInfo* ei) : pos(p) {
+  pvNode = pv;
   ttMove = ttm;
-  mateKiller = (mk == ttm)? MOVE_NONE : mk;
-  killer1 = k1;
-  killer2 = k2;
+  mateKiller = (ss.mateKiller == ttm)? MOVE_NONE : ss.mateKiller;
+  killer1 = ss.killers[0];
+  killer2 = ss.killers[1];
   depth = d;
   movesPicked = 0;
   numOfMoves = 0;
   numOfBadCaptures = 0;
-  dc = p.discovered_check_candidates(p.side_to_move());
+
+  // With EvalInfo we are able to know how many captures are possible before
+  // generating them. So avoid generating in case we know are zero.
+  Color us = pos.side_to_move();
+  Color them = opposite_color(us);
+  bool noCaptures =    ei
+                   && (ei->attackedBy[us][0] & pos.pieces_of_color(them)) == 0
+                   && !ei->mi->specialized_eval_exists()
+                   && (pos.ep_square() == SQ_NONE)
+                   && !pos.has_pawn_on_7th(us);
 
   if (p.is_check())
-    phaseIndex = EvasionsPhaseIndex;
+      phaseIndex = EvasionsPhaseIndex;
   else if (depth > Depth(0))
-    phaseIndex = MainSearchPhaseIndex;
+      phaseIndex = MainSearchPhaseIndex;
   else if (depth == Depth(0))
-    phaseIndex = QsearchWithChecksPhaseIndex;
+      phaseIndex = (noCaptures ? QsearchNoCapturesPhaseIndex : QsearchWithChecksPhaseIndex);
   else
-    phaseIndex = QsearchWithoutChecksPhaseIndex;
+      phaseIndex = (noCaptures ? NoMovesPhaseIndex : QsearchWithoutChecksPhaseIndex);
 
+  dc = p.discovered_check_candidates(us);
   pinned = p.pinned_pieces(p.side_to_move());
 
   finished = false;
@@ -211,6 +224,8 @@ void MovePicker::score_captures() {
   // where it is possible to recapture with the hanging piece). Exchanging
   // big pieces before capturing a hanging piece probably helps to reduce
   // the subtree size.
+  // While scoring captures it moves all captures with negative SEE values
+  // to the badCaptures[] array.
   Move m;
   int seeValue;
 
@@ -225,8 +240,15 @@ void MovePicker::score_captures() {
           else
               moves[i].score = int(pos.midgame_value_of_piece_on(move_to(m)))
                               -int(pos.type_of_piece_on(move_from(m)));
-      } else
+      }
+      else
+      {
+          // Losing capture, move it to the badCaptures[] array
+          assert(numOfBadCaptures < 63);
           moves[i].score = seeValue;
+          badCaptures[numOfBadCaptures++] = moves[i];
+          moves[i--] = moves[--numOfMoves];
+      }
   }
 }
 
@@ -248,10 +270,11 @@ void MovePicker::score_noncaptures() {
       else
           hs = H.move_ordering_score(pos.piece_on(move_from(m)), m);
 
-      // Ensure moves in history are always sorted as first
+      // Ensure history is always preferred to pst
       if (hs > 0)
           hs += 1000;
 
+      // pst based scoring
       moves[i].score = hs + pos.mg_pst_delta(m);
   }
 }
@@ -270,7 +293,6 @@ void MovePicker::score_evasions() {
       } else
           moves[i].score = H.move_ordering_score(pos.piece_on(move_from(m)), m);
   }
-  // FIXME try psqt also here
 }
 
 void MovePicker::score_qcaptures() {
@@ -288,8 +310,11 @@ void MovePicker::score_qcaptures() {
 }
 
 
-/// find_best_index() loops across the moves and returns index of
-/// the highest scored one.
+/// find_best_index() loops across the moves and returns index of
+/// the highest scored one. There is also a second version that
+/// lowers the priority of moves that attack the same square,
+/// so that if the best move that attack a square fails the next
+/// move picked attacks a different square if any, not the same one.
 
 int MovePicker::find_best_index() {
 
@@ -304,14 +329,48 @@ int MovePicker::find_best_index() {
   return bestIndex;
 }
 
+int MovePicker::find_best_index(Bitboard* squares, int values[]) {
+
+  int hs;
+  Move m;
+  Square to;
+  int bestScore = -10000000, bestIndex = -1;
+
+  for (int i = movesPicked; i < numOfMoves; i++)
+  {
+      m = moves[i].move;
+      to = move_to(m);
+      
+      if (!bit_is_set(*squares, to))
+      {
+          // Init at first use
+          set_bit(squares, to);
+          values[to] = 0;
+      }
+
+      hs = moves[i].score - values[to];
+      if (hs > bestScore)
+      {
+          bestIndex = i;
+          bestScore = hs;
+      }
+  }
+
+  if (bestIndex != -1)
+  {
+      // Raise value of the picked square, so next attack
+      // to the same square will get low priority.
+      to = move_to(moves[bestIndex].move);
+      values[to] += 0xB00;
+  }
+  return bestIndex;
+}
+
 
 /// MovePicker::pick_move_from_list() picks the move with the biggest score
 /// from a list of generated moves (moves[] or badCaptures[], depending on
 /// the current move generation phase).  It takes care not to return the
 /// transposition table move if that has already been serched previously.
-/// While picking captures in the PH_GOOD_CAPTURES phase (i.e. while picking
-/// non-losing captures in the main search), it moves all captures with
-/// negative SEE values to the badCaptures[] array.
 
 Move MovePicker::pick_move_from_list() {
 
@@ -325,23 +384,8 @@ Move MovePicker::pick_move_from_list() {
 
       while (movesPicked < numOfMoves)
       {
-          int bestScore = -10000000;
-          bestIndex = -1;
-          for (int i = movesPicked; i < numOfMoves; i++)
-          {
-              if (moves[i].score < 0)
-              {
-                  // Losing capture, move it to the badCaptures[] array
-                  assert(numOfBadCaptures < 63);
-                  badCaptures[numOfBadCaptures++] = moves[i];
-                  moves[i--] = moves[--numOfMoves];
-              }
-              else if (moves[i].score > bestScore)
-              {
-                  bestIndex = i;
-                  bestScore = moves[i].score;
-              }
-          }
+          bestIndex = find_best_index();
+
           if (bestIndex != -1) // Found a good capture
           {
               move = moves[bestIndex].move;
@@ -461,8 +505,9 @@ MovePicker::MovegenPhase MovePicker::current_move_type() const {
 
 /// MovePicker::init_phase_table() initializes the PhaseTable[],
 /// MainSearchPhaseIndex, EvasionPhaseIndex, QsearchWithChecksPhaseIndex
-/// and QsearchWithoutChecksPhaseIndex variables. It is only called once
-/// during program startup, and never again while the program is running.
+/// QsearchNoCapturesPhaseIndex, QsearchWithoutChecksPhaseIndex and
+/// NoMovesPhaseIndex variables. It is only called once during program
+/// startup, and never again while the program is running.
 
 void MovePicker::init_phase_table() {
 
@@ -491,8 +536,17 @@ void MovePicker::init_phase_table() {
   PhaseTable[i++] = PH_QCHECKS;
   PhaseTable[i++] = PH_STOP;
 
+  // Quiescence search with checks only and no captures
+  QsearchNoCapturesPhaseIndex = i - 1;
+  PhaseTable[i++] = PH_QCHECKS;
+  PhaseTable[i++] = PH_STOP;
+
   // Quiescence search without checks
   QsearchWithoutChecksPhaseIndex = i - 1;
   PhaseTable[i++] = PH_QCAPTURES;
   PhaseTable[i++] = PH_STOP;
+
+  // Do not generate any move
+  NoMovesPhaseIndex = i - 1;
+  PhaseTable[i++] = PH_STOP;
 }

src/movepick.h

@@ -34,6 +34,9 @@
 //// Types
 ////
 
+struct EvalInfo;
+struct SearchStack;
+
 /// MovePicker is a class which is used to pick one legal move at a time from
 /// the current position.  It is initialized with a Position object and a few
 /// moves we have reason to believe are good.  The most important method is
@@ -60,7 +63,7 @@ public:
     PH_STOP
   };
 
-  MovePicker(const Position& p, bool pvnode, Move ttm, Move mk, Move k1, Move k2, Depth d);
+  MovePicker(const Position& p, bool pvnode, Move ttm, const SearchStack& ss, Depth d, EvalInfo* ei = NULL);
   Move get_next_move();
   Move get_next_move(Lock &lock);
   int number_of_moves() const;
@@ -77,6 +80,7 @@ private:
   void score_qcaptures();
   Move pick_move_from_list();
   int find_best_index();
+  int find_best_index(Bitboard* squares, int values[]);
 
   const Position& pos;
   Move ttMove, mateKiller, killer1, killer2;

src/pawns.cpp

@@ -23,6 +23,7 @@
 ////
 
 #include <cassert>
+#include <cstring>
 
 #include "pawns.h"
 

src/piece.cpp

@@ -72,7 +72,7 @@ const SquareDelta PawnPush[2] = {
 
 static const char PieceChars[] = " pnbrqk";
 
-char piece_type_to_char(PieceType pt, bool upcase = false) {
+char piece_type_to_char(PieceType pt, bool upcase) {
   return upcase? toupper(PieceChars[pt]) : PieceChars[pt];
 }
 

src/piece.h

@@ -124,7 +124,7 @@ inline SquareDelta pawn_push(Color c) {
 //// Prototypes
 ////
 
-extern char piece_type_to_char(PieceType pt, bool upcase);
+extern char piece_type_to_char(PieceType pt, bool upcase = false);
 extern PieceType piece_type_from_char(char c);
 extern bool piece_is_ok(Piece pc);
 extern bool piece_type_is_ok(PieceType pt);

src/position.cpp

@@ -31,6 +31,7 @@
 #include "movepick.h"
 #include "position.h"
 #include "psqtab.h"
+#include "san.h"
 #include "ucioption.h"
 
 
@@ -38,6 +39,8 @@
 //// Variables
 ////
 
+extern SearchStack EmptySearchStack;
+
 int Position::castleRightsMask[64];
 
 Key Position::zobrist[2][8][64];
@@ -49,6 +52,7 @@ Key Position::zobSideToMove;
 Value Position::MgPieceSquareTable[16][64];
 Value Position::EgPieceSquareTable[16][64];
 
+static bool RequestPending = false;
 
 ////
 //// Functions
@@ -242,7 +246,7 @@ const std::string Position::to_fen() const {
 
       fen += (rank > RANK_1 ? '/' : ' ');
   }
-  fen += (sideToMove == WHITE ? 'w' : 'b') + ' ';
+  fen += (sideToMove == WHITE ? "w " : "b ");
   if (castleRights != NO_CASTLES)
   {
     if (can_castle_kingside(WHITE))  fen += 'K';
@@ -263,29 +267,45 @@ const std::string Position::to_fen() const {
 
 
 /// Position::print() prints an ASCII representation of the position to
-/// the standard output.
+/// the standard output. If a move is given then also the san is print.
 
-void Position::print() const {
-  char pieceStrings[][8] =
-    {"| ? ", "| P ", "| N ", "| B ", "| R ", "| Q ", "| K ", "| ? ",
-     "| ? ", "|=P=", "|=N=", "|=B=", "|=R=", "|=Q=", "|=K="
-    };
+void Position::print(Move m) const {
 
-  for(Rank rank = RANK_8; rank >= RANK_1; rank--) {
-    std::cout << "+---+---+---+---+---+---+---+---+\n";
-    for(File file = FILE_A; file <= FILE_H; file++) {
-      Square sq = make_square(file, rank);
-      Piece piece = piece_on(sq);
-      if(piece == EMPTY)
-        std::cout << ((square_color(sq) == WHITE)? "|   " : "| . ");
-      else
-        std::cout << pieceStrings[piece];
-    }
-    std::cout << "|\n";
+  static const std::string pieceLetters = " PNBRQK  PNBRQK .";
+
+  // Check for reentrancy, as example when called from inside
+  // MovePicker that is used also here in move_to_san()
+  if (RequestPending)
+      return;
+
+  RequestPending = true;
+
+  std::cout << std::endl;
+  if (m != MOVE_NONE)
+  {
+      std::string col = (color_of_piece_on(move_from(m)) == BLACK ? ".." : "");
+      std::cout << "Move is: " << col << move_to_san(*this, m) << std::endl;
   }
-  std::cout << "+---+---+---+---+---+---+---+---+\n";
-  std::cout << to_fen() << std::endl;
-  std::cout << key << std::endl;
+  for (Rank rank = RANK_8; rank >= RANK_1; rank--)
+  {
+      std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
+      for (File file = FILE_A; file <= FILE_H; file++)
+      {
+          Square sq = make_square(file, rank);
+          Piece piece = piece_on(sq);
+          if (piece == EMPTY && square_color(sq) == WHITE)
+              piece = NO_PIECE;
+
+          char col = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
+          std::cout << '|' << col << pieceLetters[piece] << col;
+      }
+      std::cout << '|' << std::endl;
+  }
+  std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
+            << "Fen is: " << to_fen() << std::endl
+            << "Key is: " << key << std::endl;
+
+  RequestPending = false;
 }
 
 
@@ -655,10 +675,12 @@ bool Position::move_is_check(Move m, Bitboard dcCandidates) const {
 
 
 /// Position::move_is_capture() tests whether a move from the current
-/// position is a capture.
+/// position is a capture. Move must not be MOVE_NONE.
 
 bool Position::move_is_capture(Move m) const {
 
+  assert(m != MOVE_NONE);
+
   return (   !square_is_empty(move_to(m))
           && (color_of_piece_on(move_to(m)) == opposite_color(side_to_move()))
          )
@@ -1905,8 +1927,7 @@ bool Position::is_mate() {
 
   if (is_check())
   {
-      MovePicker mp = MovePicker(*this, false, MOVE_NONE, MOVE_NONE,
-                                 MOVE_NONE, MOVE_NONE, Depth(0));
+      MovePicker mp = MovePicker(*this, false, MOVE_NONE, EmptySearchStack, Depth(0));
       return mp.get_next_move() == MOVE_NONE;
   }
   return false;

src/position.h

@@ -128,7 +128,7 @@ public:
   // Text input/output
   void from_fen(const std::string &fen);
   const std::string to_fen() const;
-  void print() const;
+  void print(Move m = MOVE_NONE) const;
 
   // Copying
   void copy(const Position &pos);
@@ -174,13 +174,13 @@ public:
   // Number of pieces of each color and type
   int piece_count(Color c, PieceType pt) const;
 
-  // The en passant square:
+  // The en passant square
   Square ep_square() const;
 
   // Current king position for each color
   Square king_square(Color c) const;
 
-  // Castling rights.
+  // Castling rights
   bool can_castle_kingside(Color c) const;
   bool can_castle_queenside(Color c) const;
   bool can_castle(Color c) const;

src/san.cpp

@@ -31,6 +31,7 @@
 #include "movepick.h"
 #include "san.h"
 
+extern SearchStack EmptySearchStack;
 
 ////
 //// Local definitions
@@ -50,7 +51,7 @@ namespace {
 
   /// Functions
 
-  Ambiguity move_ambiguity(Position &pos, Move m);
+  Ambiguity move_ambiguity(const Position& pos, Move m);
   const std::string time_string(int milliseconds);
   const std::string score_string(Value v);
 }
@@ -61,206 +62,222 @@ namespace {
 ////
 
 /// move_to_san() takes a position and a move as input, where it is assumed
-/// that the move is a legal move from the position.  The return value is
+/// that the move is a legal move from the position. The return value is
 /// a string containing the move in short algebraic notation.
 
-const std::string move_to_san(Position &pos, Move m) {
-  std::string str;
+const std::string move_to_san(const Position& pos, Move m) {
 
   assert(pos.is_ok());
   assert(move_is_ok(m));
 
-  if(m == MOVE_NONE) {
-    str = "(none)";
-    return str;
-  }
-  else if(m == MOVE_NULL) {
-    str = "(null)";
-    return str;
-  }
-  else if(move_is_long_castle(m))
-    str = "O-O-O";
-  else if(move_is_short_castle(m))
-    str = "O-O";
-  else {
-    Square from, to;
-    Piece pc;
+  std::string san = "";
 
-    from = move_from(m);
-    to = move_to(m);
-    pc = pos.piece_on(move_from(m));
-
-    str = "";
-
-    if(type_of_piece(pc) == PAWN) {
-      if(pos.move_is_capture(m))
-        str += file_to_char(square_file(move_from(m)));
-    }
-    else {
-      str += piece_type_to_char(type_of_piece(pc), true);
-
-      Ambiguity amb = move_ambiguity(pos, m);
-      switch(amb) {
-
-      case AMBIGUITY_NONE:
-        break;
-
-      case AMBIGUITY_FILE:
-        str += file_to_char(square_file(from));
-        break;
-
-      case AMBIGUITY_RANK:
-        str += rank_to_char(square_rank(from));
-        break;
-
-      case AMBIGUITY_BOTH:
-        str += square_to_string(from);
-        break;
-
-      default:
-        assert(false);
+  if (m == MOVE_NONE)
+      return "(none)";
+  else if (m == MOVE_NULL)
+      return "(null)";
+  else if (move_is_long_castle(m))
+      san = "O-O-O";
+  else if (move_is_short_castle(m))
+      san = "O-O";
+  else
+  {
+      Piece pc = pos.piece_on(move_from(m));
+      if (type_of_piece(pc) != PAWN)
+      {
+          san += piece_type_to_char(type_of_piece(pc), true);
+          Square from = move_from(m);
+          switch (move_ambiguity(pos, m)) {
+          case AMBIGUITY_NONE:
+            break;
+          case AMBIGUITY_FILE:
+            san += file_to_char(square_file(from));
+            break;
+          case AMBIGUITY_RANK:
+            san += rank_to_char(square_rank(from));
+            break;
+          case AMBIGUITY_BOTH:
+            san += square_to_string(from);
+            break;
+          default:
+            assert(false);
+          }
+      }
+      if (pos.move_is_capture(m))
+      {
+          if (type_of_piece(pc) == PAWN)
+              san += file_to_char(square_file(move_from(m)));
+          san += "x";
+      }
+      san += square_to_string(move_to(m));
+      if (move_promotion(m))
+      {
+          san += '=';
+          san += piece_type_to_char(move_promotion(m), true);
       }
-    }
-
-    if(pos.move_is_capture(m))
-      str += "x";
-
-    str += square_to_string(move_to(m));
-
-    if(move_promotion(m)) {
-      str += "=";
-      str += piece_type_to_char(move_promotion(m), true);
-    }
   }
-
   // Is the move check?  We don't use pos.move_is_check(m) here, because
   // Position::move_is_check doesn't detect all checks (not castling moves,
   // promotions and en passant captures).
   UndoInfo u;
-  pos.do_move(m, u);
-  if(pos.is_check())
-    str += pos.is_mate()? "#" : "+";
-  pos.undo_move(m, u);
+  Position p(pos);
+  p.do_move(m, u);
+  if (p.is_check())
+      san += p.is_mate()? "#" : "+";
 
-  return str;
+  return san;
 }
 
 
 /// move_from_san() takes a position and a string as input, and tries to
-/// interpret the string as a move in short algebraic notation.  On success,
+/// interpret the string as a move in short algebraic notation. On success,
 /// the move is returned.  On failure (i.e. if the string is unparsable, or
 /// if the move is illegal or ambiguous), MOVE_NONE is returned.
 
-Move move_from_san(Position &pos, const std::string &movestr) {
+Move move_from_san(const Position& pos, const std::string& movestr) {
+
   assert(pos.is_ok());
 
-  MovePicker mp = MovePicker(pos, false, MOVE_NONE, MOVE_NONE, MOVE_NONE,
-                             MOVE_NONE, OnePly);
+  MovePicker mp = MovePicker(pos, false, MOVE_NONE, EmptySearchStack, OnePly);
 
   // Castling moves
-  if(movestr == "O-O-O") {
-    Move m;
-    while((m = mp.get_next_move()) != MOVE_NONE)
-      if(move_is_long_castle(m) && pos.pl_move_is_legal(m))
-        return m;
-    return MOVE_NONE;
-  }
-  else if(movestr == "O-O") {
-    Move m;
-    while((m = mp.get_next_move()) != MOVE_NONE)
-      if(move_is_short_castle(m) && pos.pl_move_is_legal(m))
-        return m;
-    return MOVE_NONE;
-  }
+  if (movestr == "O-O-O" || movestr == "O-O-O+")
+  {
+      Move m;
+      while ((m = mp.get_next_move()) != MOVE_NONE)
+          if (move_is_long_castle(m) && pos.pl_move_is_legal(m))
+              return m;
 
-  // Normal moves
-  const char *cstr = movestr.c_str();
-  const char *c;
-  char *cc;
-  char str[10];
-  int i;
-
-  // Initialize str[] by making a copy of movestr with the characters
-  // 'x', '=', '+' and '#' removed.
-  cc = str;
-  for(i=0, c=cstr; i<10 && *c!='\0' && *c!='\n' && *c!=' '; i++, c++)
-    if(!strchr("x=+#", *c)) {
-      *cc = strchr("nrq", *c)? toupper(*c) : *c;
-      cc++;
-    }
-  *cc = '\0';
-
-  size_t left = 0, right = strlen(str) - 1;
-  PieceType pt = NO_PIECE_TYPE, promotion;
-  Square to;
-  File fromFile = FILE_NONE;
-  Rank fromRank = RANK_NONE;
-
-  // Promotion?
-  if(strchr("BNRQ", str[right])) {
-    promotion = piece_type_from_char(str[right]);
-    right--;
-  }
-  else
-    promotion = NO_PIECE_TYPE;
-
-  // Find the moving piece:
-  if(left < right) {
-    if(strchr("BNRQK", str[left])) {
-      pt = piece_type_from_char(str[left]);
-      left++;
-    }
-    else
-      pt = PAWN;
-  }
-
-  // Find the to square:
-  if(left < right) {
-    if(str[right] < '1' || str[right] > '8' ||
-       str[right-1] < 'a' || str[right-1] > 'h')
       return MOVE_NONE;
-    to = make_square(file_from_char(str[right-1]), rank_from_char(str[right]));
-    right -= 2;
   }
-  else
+  else if (movestr == "O-O" || movestr == "O-O+")
+  {
+      Move m;
+      while ((m = mp.get_next_move()) != MOVE_NONE)
+          if (move_is_short_castle(m) && pos.pl_move_is_legal(m))
+              return m;
+
     return MOVE_NONE;
-
-  // Find the file and/or rank of the from square:
-  if(left <= right) {
-    if(strchr("abcdefgh", str[left])) {
-      fromFile = file_from_char(str[left]);
-      left++;
-    }
-    if(strchr("12345678", str[left]))
-      fromRank = rank_from_char(str[left]);
   }
 
-  // Look for a matching move:
+  // Normal moves. We use a simple FSM to parse the san string.
+  enum { START, TO_FILE, TO_RANK, PROMOTION_OR_CHECK, PROMOTION, CHECK, END };
+  static const std::string pieceLetters = "KQRBN";
+  PieceType pt = NO_PIECE_TYPE, promotion = NO_PIECE_TYPE;
+  File fromFile = FILE_NONE, toFile = FILE_NONE;
+  Rank fromRank = RANK_NONE, toRank = RANK_NONE;
+  Square to;
+  int state = START;
+
+  for (size_t i = 0; i < movestr.length(); i++)
+  {
+      char type, c = movestr[i];
+      if (pieceLetters.find(c) != std::string::npos)
+          type = 'P';
+      else if (c >= 'a' && c <= 'h')
+          type = 'F';
+      else if (c >= '1' && c <= '8')
+          type = 'R';
+      else
+          type = c;
+
+      switch (type) {
+      case 'P':
+          if (state == START)
+          {
+              pt = piece_type_from_char(c);
+              state = TO_FILE;
+          }
+          else if (state == PROMOTION)
+          {
+              promotion = piece_type_from_char(c);
+              state = (i < movestr.length() - 1) ? CHECK : END;
+          }
+          else
+              return MOVE_NONE;
+          break;
+      case 'F':
+          if (state == START)
+          {
+              pt = PAWN;
+              fromFile = toFile = file_from_char(c);
+              state = TO_RANK;
+          }
+          else if (state == TO_FILE)
+          {
+              toFile = file_from_char(c);
+              state = TO_RANK;
+          }
+          else if (state == TO_RANK && toFile != FILE_NONE)
+          {
+              // Previous file was for disambiguation
+              fromFile = toFile;
+              toFile = file_from_char(c);
+          }
+          else
+              return MOVE_NONE;
+          break;
+      case 'R':
+          if (state == TO_RANK)
+          {
+              toRank = rank_from_char(c);
+              state = (i < movestr.length() - 1) ? PROMOTION_OR_CHECK : END;
+          }
+          else if (state == TO_FILE && fromRank == RANK_NONE)
+          {
+              // It's a disambiguation rank instead of a file
+              fromRank = rank_from_char(c);
+          }
+          else
+              return MOVE_NONE;
+          break;
+      case 'x': case 'X':
+          if (state == TO_RANK)
+          {
+              // Previous file was for disambiguation, or it's a pawn capture
+              fromFile = toFile;
+              state = TO_FILE;
+          }
+          else if (state != TO_FILE)
+              return MOVE_NONE;
+          break;
+      case '=':
+          if (state == PROMOTION_OR_CHECK)
+              state = PROMOTION;
+          else
+              return MOVE_NONE;
+          break;
+      case '+': case '#':
+          if (state == PROMOTION_OR_CHECK || state == CHECK)
+              state = END;
+          else
+              return MOVE_NONE;
+          break;
+      default:
+          return MOVE_NONE;
+          break;
+      }
+  }
+
+  if (state != END)
+      return MOVE_NONE;
+
+  // Look for a matching move
   Move m, move = MOVE_NONE;
+  to = make_square(toFile, toRank);
   int matches = 0;
 
-  while((m = mp.get_next_move()) != MOVE_NONE) {
-    bool match = true;
-    if(pos.type_of_piece_on(move_from(m)) != pt)
-      match = false;
-    else if(move_to(m) != to)
-      match = false;
-    else if(move_promotion(m) != promotion)
-      match = false;
-    else if(fromFile != FILE_NONE && fromFile != square_file(move_from(m)))
-      match = false;
-    else if(fromRank != RANK_NONE && fromRank != square_rank(move_from(m)))
-      match = false;
-    if(match) {
-      move = m;
-      matches++;
-    }
-  }
-
-  if(matches == 1)
-    return move;
-  else
-    return MOVE_NONE;
+  while ((m = mp.get_next_move()) != MOVE_NONE)
+      if (   pos.type_of_piece_on(move_from(m)) == pt
+          && move_to(m) == to
+          && move_promotion(m) == promotion
+          && (fromFile == FILE_NONE || fromFile == square_file(move_from(m)))
+          && (fromRank == RANK_NONE || fromRank == square_rank(move_from(m))))
+      {
+          move = m;
+          matches++;
+      }
+  return (matches == 1 ? move : MOVE_NONE);
 }
 
 
@@ -271,34 +288,31 @@ Move move_from_san(Position &pos, const std::string &movestr) {
 /// length of 80 characters.  After a line break, 'startColumn' spaces are
 /// inserted at the beginning of the new line.
 
-const std::string line_to_san(const Position &pos, Move line[], int startColumn,
-                              bool breakLines) {
-  Position p = Position(pos);
+const std::string line_to_san(const Position& pos, Move line[], int startColumn, bool breakLines) {
+
   UndoInfo u;
   std::stringstream s;
   std::string moveStr;
-  size_t length, maxLength;
+  size_t length = 0;
+  size_t maxLength = 80 - startColumn;
+  Position p(pos);
 
-  length = 0;
-  maxLength = 80 - startColumn;
+  for (int i = 0; line[i] != MOVE_NONE; i++)
+  {
+      moveStr = move_to_san(p, line[i]);
+      length += moveStr.length() + 1;
+      if (breakLines && length > maxLength)
+      {
+          s << '\n' << std::setw(startColumn) << ' ';
+          length = moveStr.length() + 1;
+      }
+      s << moveStr << ' ';
 
-  for(int i = 0; line[i] != MOVE_NONE; i++) {
-    moveStr = move_to_san(p, line[i]);
-    length += moveStr.length() + 1;
-    if(breakLines && length > maxLength) {
-      s << "\n";
-      for(int j = 0; j < startColumn; j++)
-        s << " ";
-      length = moveStr.length() + 1;
-    }
-    s << moveStr << " ";
-
-    if(line[i] == MOVE_NULL)
-      p.do_null_move(u);
-    else
-      p.do_move(line[i], u);
+      if (line[i] == MOVE_NULL)
+          p.do_null_move(u);
+      else
+          p.do_move(line[i], u);
   }
-
   return s.str();
 }
 
@@ -307,26 +321,26 @@ const std::string line_to_san(const Position &pos, Move line[], int startColumn,
 /// It is used to write search information to the log file (which is created
 /// when the UCI parameter "Use Search Log" is "true").
 
-const std::string pretty_pv(const Position &pos, int time, int depth,
+const std::string pretty_pv(const Position& pos, int time, int depth,
                             uint64_t nodes, Value score, Move pv[]) {
   std::stringstream s;
 
   // Depth
-  s << std::setw(2) << std::setfill(' ') << depth << "  ";
+  s << std::setw(2) << depth << "  ";
 
   // Score
   s << std::setw(8) << score_string(score);
 
   // Time
-  s << std::setw(8) << std::setfill(' ') << time_string(time) << " ";
+  s << std::setw(8) << time_string(time) << " ";
 
   // Nodes
-  if(nodes < 1000000ULL)
-    s << std::setw(8) << std::setfill(' ') << nodes << " ";
-  else if(nodes < 1000000000ULL)
-    s << std::setw(7) << std::setfill(' ') << nodes/1000ULL << 'k' << " ";
+  if (nodes < 1000000ULL)
+    s << std::setw(8) << nodes << " ";
+  else if (nodes < 1000000000ULL)
+    s << std::setw(7) << nodes/1000ULL << 'k' << " ";
   else
-    s << std::setw(7) << std::setfill(' ') << nodes/1000000ULL << 'M' << " ";
+    s << std::setw(7) << nodes/1000000ULL << 'M' << " ";
 
   // PV
   s << line_to_san(pos, pv, 30, true);
@@ -337,82 +351,80 @@ const std::string pretty_pv(const Position &pos, int time, int depth,
 
 namespace {
 
-  Ambiguity move_ambiguity(Position &pos, Move m) {
-    Square from, to;
-    Piece pc;
+  Ambiguity move_ambiguity(const Position& pos, Move m) {
 
-    from = move_from(m);
-    to = move_to(m);
-    pc = pos.piece_on(from);
+    Square from = move_from(m);
+    Square to = move_to(m);
+    Piece pc = pos.piece_on(from);
 
     // King moves are never ambiguous, because there is never two kings of
     // the same color.
-    if(type_of_piece(pc) == KING)
-      return AMBIGUITY_NONE;
+    if (type_of_piece(pc) == KING)
+        return AMBIGUITY_NONE;
 
-    MovePicker mp = MovePicker(pos, false, MOVE_NONE, MOVE_NONE, MOVE_NONE,
-                               MOVE_NONE, OnePly);
+    MovePicker mp = MovePicker(pos, false, MOVE_NONE, EmptySearchStack, OnePly);
     Move mv, moveList[8];
-    int i, j, n;
 
-    n = 0;
-    while((mv = mp.get_next_move()) != MOVE_NONE)
-      if(move_to(mv) == to && pos.piece_on(move_from(mv)) == pc
-         && pos.pl_move_is_legal(mv))
-        moveList[n++] = mv;
-    if(n == 1)
-      return AMBIGUITY_NONE;
+    int n = 0;
+    while ((mv = mp.get_next_move()) != MOVE_NONE)
+        if (move_to(mv) == to && pos.piece_on(move_from(mv)) == pc && pos.pl_move_is_legal(mv))
+            moveList[n++] = mv;
 
-    j = 0;
-    for(i = 0; i < n; i++)
-      if(square_file(move_from(moveList[i])) == square_file(from))
-        j++;
-    if(j == 1)
-      return AMBIGUITY_FILE;
+    if (n == 1)
+        return AMBIGUITY_NONE;
 
-    j = 0;
-    for(i = 0; i < n; i++)
-      if(square_rank(move_from(moveList[i])) == square_rank(from))
-        j++;
-    if(j == 1)
-      return AMBIGUITY_RANK;
+    int f = 0, r = 0;
+    for (int i = 0; i < n; i++)
+    {
+        if (square_file(move_from(moveList[i])) == square_file(from))
+            f++;
+
+        if (square_rank(move_from(moveList[i])) == square_rank(from))
+            r++;
+    }
+    if (f == 1)
+        return AMBIGUITY_FILE;
+
+    if (r == 1)
+        return AMBIGUITY_RANK;
 
     return AMBIGUITY_BOTH;
   }
 
 
   const std::string time_string(int milliseconds) {
+
     std::stringstream s;
+    s << std::setfill('0');
 
-    int hours = milliseconds / (1000 * 60 * 60);
-    int minutes = (milliseconds - hours*1000*60*60) / (60*1000);
-    int seconds = (milliseconds - hours*1000*60*60 - minutes*60*1000) / 1000;
+    int hours = milliseconds / (1000*60*60);
+    int minutes = (milliseconds - hours*1000*60*60) / (1000*60);
+    int seconds = (milliseconds - hours*1000*60*60 - minutes*1000*60) / 1000;
 
-    if(hours)
-      s << hours << ':';
-    s << std::setw(2) << std::setfill('0') << minutes << ':';
-    s << std::setw(2) << std::setfill('0') << seconds;
+    if (hours)
+        s << hours << ':';
 
+    s << std::setw(2) << minutes << ':' << std::setw(2) << seconds;
     return s.str();
   }
 
 
   const std::string score_string(Value v) {
+
     std::stringstream s;
 
-    if(abs(v) >= VALUE_MATE - 200) {
-      if(v < 0)
-        s << "-#" << (VALUE_MATE + v) / 2;
-      else
+    if (v >= VALUE_MATE - 200)
         s << "#" << (VALUE_MATE - v + 1) / 2;
-    }
-    else {
-      float floatScore = float(v) / float(PawnValueMidgame);
-      if(v >= 0)
-        s << '+';
-      s << std::setprecision(2) << std::fixed << floatScore;
+    else if(v <= -VALUE_MATE + 200)
+        s << "-#" << (VALUE_MATE + v) / 2;
+    else
+    {
+        float floatScore = float(v) / float(PawnValueMidgame);
+        if (v >= 0)
+            s << '+';
+
+        s << std::setprecision(2) << std::fixed << floatScore;
     }
     return s.str();
   }
-
 }

src/san.h

@@ -36,12 +36,9 @@
 //// Prototypes
 ////
 
-extern const std::string move_to_san(Position &pos, Move m);
-extern Move move_from_san(Position &pos, const std::string &str);
-extern const std::string line_to_san(const Position &pos, Move line[],
-                                     int startColumn, bool breakLines);
-extern const std::string pretty_pv(const Position &pos, int time, int depth,
-                                   uint64_t nodes, Value score, Move pv[]);
-
+extern const std::string move_to_san(const Position& pos, Move m);
+extern Move move_from_san(const Position& pos, const std::string& str);
+extern const std::string line_to_san(const Position& pos, Move line[], int startColumn, bool breakLines);
+extern const std::string pretty_pv(const Position& pos, int time, int depth, uint64_t nodes, Value score, Move pv[]);
 
 #endif // !defined(SAN_H_INCLUDED)

src/search.cpp

@@ -106,6 +106,9 @@ namespace {
   const bool UseIIDAtPVNodes = true;
   const bool UseIIDAtNonPVNodes = false;
 
+  // Use null move driven internal iterative deepening?
+  bool UseNullDrivenIID = true;
+
   // Internal iterative deepening margin.  At Non-PV moves, when
   // UseIIDAtNonPVNodes is true, we do an internal iterative deepening search
   // when the static evaluation is at most IIDMargin below beta.
@@ -144,7 +147,7 @@ namespace {
   bool UseFutilityPruning = true;
 
   // Margins for futility pruning in the quiescence search, at frontier
-  // nodes, and at pre-frontier nodes:
+  // nodes, and at pre-frontier nodes
   Value FutilityMargin0 = Value(0x80);
   Value FutilityMargin1 = Value(0x100);
   Value FutilityMargin2 = Value(0x300);
@@ -167,27 +170,28 @@ namespace {
   Depth PawnEndgameExtension[2] = {OnePly, OnePly};
   Depth MateThreatExtension[2] = {Depth(0), Depth(0)};
 
-  // Search depth at iteration 1:
+  // Search depth at iteration 1
   const Depth InitialDepth = OnePly /*+ OnePly/2*/;
 
   // Node counters
   int NodesSincePoll;
   int NodesBetweenPolls = 30000;
 
-  // Iteration counter:
+  // Iteration counter
   int Iteration;
+  bool LastIterations;
 
   // Scores and number of times the best move changed for each iteration:
   Value ValueByIteration[PLY_MAX_PLUS_2];
   int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
 
-  // MultiPV mode:
+  // MultiPV mode
   int MultiPV = 1;
 
   // Time managment variables
   int SearchStartTime;
   int MaxNodes, MaxDepth;
-  int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, TimeAdvantage;
+  int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
   Move BestRootMove, PonderMove, EasyMove;
   int RootMoveNumber;
   bool InfiniteSearch;
@@ -237,19 +241,20 @@ namespace {
                 Depth depth, int ply, int threadID);
   void sp_search(SplitPoint *sp, int threadID);
   void sp_search_pv(SplitPoint *sp, int threadID);
+  void init_search_stack(SearchStack& ss);
   void init_search_stack(SearchStack ss[]);
   void init_node(const Position &pos, SearchStack ss[], int ply, int threadID);
   void update_pv(SearchStack ss[], int ply);
   void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
   bool connected_moves(const Position &pos, Move m1, Move m2);
-  Depth extension(const Position &pos, Move m, bool pvNode, bool check,
-                  bool singleReply, bool mateThreat);
+  bool move_is_killer(Move m, const SearchStack& ss);
+  Depth extension(const Position &pos, Move m, bool pvNode, bool check, bool singleReply, bool mateThreat, bool* dangerous);
   bool ok_to_do_nullmove(const Position &pos);
   bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
   bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
   bool ok_to_history(const Position &pos, Move m);
-  void update_history(const Position& pos, Move m, Depth depth,
-                      Move movesSearched[], int moveCount);
+  void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
+  void update_killers(Move m, SearchStack& ss);
 
   bool fail_high_ply_1();
   int current_search_time();
@@ -297,6 +302,9 @@ Lock IOLock;
 
 History H;  // Should be made local?
 
+// The empty search stack
+SearchStack EmptySearchStack;
+
 
 ////
 //// Functions
@@ -385,6 +393,7 @@ void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
   if (UseLogFile)
       LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
 
+  UseNullDrivenIID = get_option_value_bool("Null driven IID");
   UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)");
   UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)");
 
@@ -422,16 +431,14 @@ void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
   int myIncrement = increment[side_to_move];
   int oppTime = time[1 - side_to_move];
 
-  TimeAdvantage = myTime - oppTime;
-
   if (!movesToGo) // Sudden death time control
-  { 
-      if (increment)
+  {
+      if (myIncrement)
       {
           MaxSearchTime = myTime / 30 + myIncrement;
           AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
       } else { // Blitz game without increment
-          MaxSearchTime = myTime / 40;
+          MaxSearchTime = myTime / 30;
           AbsoluteMaxSearchTime = myTime / 8;
       }
   }
@@ -561,6 +568,9 @@ void init_threads() {
       // Wait until the thread has finished launching:
       while (!Threads[i].running);
   }
+
+  // Init also the empty search stack
+  init_search_stack(EmptySearchStack);
 }
 
 
@@ -617,6 +627,7 @@ namespace {
     ValueByIteration[0] = Value(0);
     ValueByIteration[1] = rml.get_move_score(0);
     Iteration = 1;
+    LastIterations = false;
 
     EasyMove = rml.scan_for_easy_move();
 
@@ -671,9 +682,8 @@ namespace {
                 ExtraSearchTime = BestMoveChangesByIteration[Iteration]   * (MaxSearchTime / 2)
                                 + BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
 
-            // If we need some more and we are in time advantage take it
-            if (ExtraSearchTime > 0 && TimeAdvantage > 2 * MaxSearchTime)
-                ExtraSearchTime += MaxSearchTime / 2;
+            // Try to guess if the current iteration is the last one or the last two
+            LastIterations = (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*58) / 128);
 
             // Stop search if most of MaxSearchTime is consumed at the end of the
             // iteration.  We probably don't have enough time to search the first
@@ -766,7 +776,8 @@ namespace {
                       << " currmovenumber " << i + 1 << std::endl;
 
         // Decide search depth for this move
-        ext = extension(pos, move, true, pos.move_is_check(move), false, false);
+        bool dangerous;
+        ext = extension(pos, move, true, pos.move_is_check(move), false, false, &dangerous);
         newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
 
         // Make the move, and search it
@@ -783,7 +794,7 @@ namespace {
 
             if (Problem && StopOnPonderhit)
                 StopOnPonderhit = false;
-        } 
+        }
         else
         {
             value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
@@ -933,16 +944,14 @@ namespace {
 
     // Initialize a MovePicker object for the current position, and prepare
     // to search all moves
-    MovePicker mp = MovePicker(pos, true, ttMove, ss[ply].mateKiller,
-                               ss[ply].killer1, ss[ply].killer2, depth);
+    MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
 
     Move move, movesSearched[256];
     int moveCount = 0;
     Value value, bestValue = -VALUE_INFINITE;
     Bitboard dcCandidates = mp.discovered_check_candidates();
     bool isCheck = pos.is_check();
-    bool mateThreat =   MateThreatExtension[1] > Depth(0)
-                     && pos.has_mate_threat(opposite_color(pos.side_to_move()));
+    bool mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
 
     // Loop through all legal moves until no moves remain or a beta cutoff
     // occurs.
@@ -955,7 +964,6 @@ namespace {
       bool singleReply = (isCheck && mp.number_of_moves() == 1);
       bool moveIsCheck = pos.move_is_check(move, dcCandidates);
       bool moveIsCapture = pos.move_is_capture(move);
-      bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
 
       movesSearched[moveCount++] = ss[ply].currentMove = move;
 
@@ -967,7 +975,8 @@ namespace {
           ss[ply].currentMoveCaptureValue = Value(0);
 
       // Decide the new search depth
-      Depth ext = extension(pos, move, true, moveIsCheck, singleReply, mateThreat);
+      bool dangerous;
+      Depth ext = extension(pos, move, true, moveIsCheck, singleReply, mateThreat, &dangerous);
       Depth newDepth = depth - OnePly + ext;
 
       // Make and search the move
@@ -981,14 +990,12 @@ namespace {
         // Try to reduce non-pv search depth by one ply if move seems not problematic,
         // if the move fails high will be re-searched at full depth.
         if (    depth >= 2*OnePly
-            &&  ext == Depth(0)
             &&  moveCount >= LMRPVMoves
+            && !dangerous
             && !moveIsCapture
             && !move_promotion(move)
-            && !moveIsPassedPawnPush
             && !move_is_castle(move)
-            &&  move != ss[ply].killer1
-            &&  move != ss[ply].killer2)
+            && !move_is_killer(move, ss[ply]))
         {
             ss[ply].reduction = OnePly;
             value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
@@ -1070,11 +1077,7 @@ namespace {
         if (ok_to_history(pos, m)) // Only non capture moves are considered
         {
             update_history(pos, m, depth, movesSearched, moveCount);
-            if (m != ss[ply].killer1)
-            {
-                ss[ply].killer2 = ss[ply].killer1;
-                ss[ply].killer1 = m;
-            }
+            update_killers(m, ss[ply]);
         }
         TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
     }
@@ -1125,12 +1128,13 @@ namespace {
 
     if (tte && ok_to_use_TT(tte, depth, beta, ply))
     {
-        ss[ply].currentMove = ttMove; // can be MOVE_NONE ?
+        ss[ply].currentMove = ttMove; // can be MOVE_NONE
         return value_from_tt(tte->value(), ply);
     }
 
     Value approximateEval = quick_evaluate(pos);
     bool mateThreat = false;
+    bool nullDrivenIID = false;
     bool isCheck = pos.is_check();
 
     // Null move search
@@ -1143,7 +1147,22 @@ namespace {
 
         UndoInfo u;
         pos.do_null_move(u);
-        Value nullValue = -search(pos, ss, -(beta-1), depth-4*OnePly, ply+1, false, threadID);
+        int R = (depth > 7 ? 4 : 3);
+
+        Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
+
+        // Check for a null capture artifact, if the value without the null capture
+        // is above beta then there is a good possibility that this is a cut-node.
+        // We will do an IID later to find a ttMove.
+        if (   UseNullDrivenIID
+            && nullValue < beta
+            && depth > 6 * OnePly
+            && ttMove == MOVE_NONE
+            && ss[ply + 1].currentMove != MOVE_NONE
+            && pos.move_is_capture(ss[ply + 1].currentMove)
+            && pos.see(ss[ply + 1].currentMove) * PawnValueMidgame + nullValue > beta - IIDMargin)
+            nullDrivenIID = true;
+
         pos.undo_null_move(u);
 
         if (nullValue >= beta)
@@ -1163,8 +1182,10 @@ namespace {
             // low score (which will cause the reduced move to fail high in the
             // parent node, which will trigger a re-search with full depth).
             if (nullValue == value_mated_in(ply + 2))
+            {
                 mateThreat = true;
-
+                nullDrivenIID = false;
+            }
             ss[ply].threatMove = ss[ply + 1].currentMove;
             if (   depth < ThreatDepth
                 && ss[ply - 1].reduction
@@ -1188,11 +1209,23 @@ namespace {
         search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
         ttMove = ss[ply].pv[ply];
     }
+    else if (nullDrivenIID)
+    {
+        // The null move failed low due to a suspicious capture. Perhaps we
+        // are facing a null capture artifact due to the side to move change
+        // and this is a cut-node. So it's a good time to search for a ttMove.
+        Move tm = ss[ply].threatMove;
+
+        assert(tm != MOVE_NONE);
+
+        search(pos, ss, beta, Min(depth/2, depth-3*OnePly), ply, false, threadID);
+        ttMove = ss[ply].pv[ply];
+        ss[ply].threatMove = tm;
+    }
 
     // Initialize a MovePicker object for the current position, and prepare
     // to search all moves:
-    MovePicker mp = MovePicker(pos, false, ttMove, ss[ply].mateKiller,
-                               ss[ply].killer1, ss[ply].killer2, depth);
+    MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth);
 
     Move move, movesSearched[256];
     int moveCount = 0;
@@ -1214,19 +1247,18 @@ namespace {
       bool singleReply = (isCheck && mp.number_of_moves() == 1);
       bool moveIsCheck = pos.move_is_check(move, dcCandidates);
       bool moveIsCapture = pos.move_is_capture(move);
-      bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
 
       movesSearched[moveCount++] = ss[ply].currentMove = move;
 
       // Decide the new search depth
-      Depth ext = extension(pos, move, false, moveIsCheck, singleReply, mateThreat);
+      bool dangerous;
+      Depth ext = extension(pos, move, false, moveIsCheck, singleReply, mateThreat, &dangerous);
       Depth newDepth = depth - OnePly + ext;
 
       // Futility pruning
       if (    useFutilityPruning
-          &&  ext == Depth(0)
+          && !dangerous
           && !moveIsCapture
-          && !moveIsPassedPawnPush
           && !move_promotion(move))
       {
           if (   moveCount >= 2 + int(depth)
@@ -1254,15 +1286,13 @@ namespace {
 
       // Try to reduce non-pv search depth by one ply if move seems not problematic,
       // if the move fails high will be re-searched at full depth.
-      if (   depth >= 2*OnePly
-          && ext == Depth(0)
-          && moveCount >= LMRNonPVMoves
+      if (    depth >= 2*OnePly
+          &&  moveCount >= LMRNonPVMoves
+          && !dangerous
           && !moveIsCapture
           && !move_promotion(move)
-          && !moveIsPassedPawnPush
           && !move_is_castle(move)
-          &&  move != ss[ply].killer1
-          &&  move != ss[ply].killer2)
+          && !move_is_killer(move, ss[ply]))
       {
           ss[ply].reduction = OnePly;
           value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
@@ -1321,11 +1351,7 @@ namespace {
         if (ok_to_history(pos, m)) // Only non capture moves are considered
         {
             update_history(pos, m, depth, movesSearched, moveCount);
-            if (m != ss[ply].killer1)
-            {
-                ss[ply].killer2 = ss[ply].killer1;
-                ss[ply].killer1 = m;
-            }
+            update_killers(m, ss[ply]);
         }
         TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
     }
@@ -1382,12 +1408,13 @@ namespace {
     // Initialize a MovePicker object for the current position, and prepare
     // to search the moves.  Because the depth is <= 0 here, only captures,
     // queen promotions and checks (only if depth == 0) will be generated.
-    MovePicker mp = MovePicker(pos, false, MOVE_NONE, MOVE_NONE, MOVE_NONE,
-                               MOVE_NONE, depth);
+    MovePicker mp = MovePicker(pos, false, MOVE_NONE, EmptySearchStack, depth, &ei);
     Move move;
     int moveCount = 0;
     Bitboard dcCandidates = mp.discovered_check_candidates();
     bool isCheck = pos.is_check();
+    bool pvNode = (beta - alpha != 1);
+    bool enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
 
     // Loop through the moves until no moves remain or a beta cutoff
     // occurs.
@@ -1396,20 +1423,17 @@ namespace {
     {
       assert(move_is_ok(move));
 
-      bool moveIsCheck = pos.move_is_check(move, dcCandidates);
-      bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
-
       moveCount++;
       ss[ply].currentMove = move;
 
       // Futility pruning
       if (    UseQSearchFutilityPruning
+          &&  enoughMaterial
           && !isCheck
-          && !moveIsCheck
+          && !pvNode
           && !move_promotion(move)
-          && !moveIsPassedPawnPush
-          &&  beta - alpha == 1
-          &&  pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame)
+          && !pos.move_is_check(move, dcCandidates)
+          && !pos.move_is_passed_pawn_push(move))
       {
           Value futilityValue = staticValue
                               + Max(pos.midgame_value_of_piece_on(move_to(move)),
@@ -1425,7 +1449,7 @@ namespace {
           }
       }
 
-      // Don't search captures and checks with negative SEE values.
+      // Don't search captures and checks with negative SEE values
       if (   !isCheck
           && !move_promotion(move)
           && (pos.midgame_value_of_piece_on(move_from(move)) >
@@ -1463,6 +1487,13 @@ namespace {
     // Update transposition table
     TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_EXACT);
 
+    // Update killers only for good check moves
+    Move m = ss[ply].currentMove;
+    if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
+    {
+        // Wrong to update history when depth is <= 0
+        update_killers(m, ss[ply]);
+    }
     return bestValue;
   }
 
@@ -1497,7 +1528,6 @@ namespace {
 
       bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
       bool moveIsCapture = pos.move_is_capture(move);
-      bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
 
       lock_grab(&(sp->lock));
       int moveCount = ++sp->moves;
@@ -1506,14 +1536,14 @@ namespace {
       ss[sp->ply].currentMove = move;
 
       // Decide the new search depth.
-      Depth ext = extension(pos, move, false, moveIsCheck, false, false);
+      bool dangerous;
+      Depth ext = extension(pos, move, false, moveIsCheck, false, false, &dangerous);
       Depth newDepth = sp->depth - OnePly + ext;
 
       // Prune?
       if (    useFutilityPruning
-          &&  ext == Depth(0)
+          && !dangerous
           && !moveIsCapture
-          && !moveIsPassedPawnPush
           && !move_promotion(move)
           &&  moveCount >= 2 + int(sp->depth)
           &&  ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
@@ -1525,14 +1555,12 @@ namespace {
 
       // Try to reduce non-pv search depth by one ply if move seems not problematic,
       // if the move fails high will be re-searched at full depth.
-      if (    ext == Depth(0)
+      if (   !dangerous
           &&  moveCount >= LMRNonPVMoves
           && !moveIsCapture
-          && !moveIsPassedPawnPush
           && !move_promotion(move)
           && !move_is_castle(move)
-          &&  move != ss[sp->ply].killer1
-          &&  move != ss[sp->ply].killer2)
+          && !move_is_killer(move, ss[sp->ply]))
       {
           ss[sp->ply].reduction = OnePly;
           value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
@@ -1610,7 +1638,6 @@ namespace {
     {
       bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
       bool moveIsCapture = pos.move_is_capture(move);
-      bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
 
       assert(move_is_ok(move));
 
@@ -1624,7 +1651,8 @@ namespace {
       ss[sp->ply].currentMove = move;
 
       // Decide the new search depth.
-      Depth ext = extension(pos, move, true, moveIsCheck, false, false);
+      bool dangerous;
+      Depth ext = extension(pos, move, true, moveIsCheck, false, false, &dangerous);
       Depth newDepth = sp->depth - OnePly + ext;
 
       // Make and search the move.
@@ -1633,14 +1661,12 @@ namespace {
 
       // Try to reduce non-pv search depth by one ply if move seems not problematic,
       // if the move fails high will be re-searched at full depth.
-      if (    ext == Depth(0)
+      if (   !dangerous
           &&  moveCount >= LMRPVMoves
           && !moveIsCapture
-          && !moveIsPassedPawnPush
           && !move_promotion(move)
           && !move_is_castle(move)
-          &&  move != ss[sp->ply].killer1
-          &&  move != ss[sp->ply].killer2)
+          && !move_is_killer(move, ss[sp->ply]))
       {
           ss[sp->ply].reduction = OnePly;
           value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
@@ -1871,17 +1897,28 @@ namespace {
 
   // init_search_stack() initializes a search stack at the beginning of a
   // new search from the root.
+  void init_search_stack(SearchStack& ss) {
+
+    ss.pv[0] = MOVE_NONE;
+    ss.pv[1] = MOVE_NONE;
+    ss.currentMove = MOVE_NONE;
+    ss.threatMove = MOVE_NONE;
+    ss.reduction = Depth(0);
+    for (int j = 0; j < KILLER_MAX; j++)
+        ss.killers[j] = MOVE_NONE;
+  }
 
   void init_search_stack(SearchStack ss[]) {
-    for(int i = 0; i < 3; i++) {
-      ss[i].pv[i] = MOVE_NONE;
-      ss[i].pv[i+1] = MOVE_NONE;
-      ss[i].currentMove = MOVE_NONE;
-      ss[i].mateKiller = MOVE_NONE;
-      ss[i].killer1 = MOVE_NONE;
-      ss[i].killer2 = MOVE_NONE;
-      ss[i].threatMove = MOVE_NONE;
-      ss[i].reduction = Depth(0);
+
+    for (int i = 0; i < 3; i++)
+    {
+        ss[i].pv[i] = MOVE_NONE;
+        ss[i].pv[i+1] = MOVE_NONE;
+        ss[i].currentMove = MOVE_NONE;
+        ss[i].threatMove = MOVE_NONE;
+        ss[i].reduction = Depth(0);
+        for (int j = 0; j < KILLER_MAX; j++)
+            ss[i].killers[j] = MOVE_NONE;
     }
   }
 
@@ -1905,13 +1942,13 @@ namespace {
         NodesSincePoll = 0;
       }
     }
-
     ss[ply].pv[ply] = ss[ply].pv[ply+1] = ss[ply].currentMove = MOVE_NONE;
     ss[ply+2].mateKiller = MOVE_NONE;
-    ss[ply+2].killer1 = ss[ply+2].killer2 = MOVE_NONE;
     ss[ply].threatMove = MOVE_NONE;
     ss[ply].reduction = Depth(0);
     ss[ply].currentMoveCaptureValue = Value(0);
+    for (int j = 0; j < KILLER_MAX; j++)
+        ss[ply+2].killers[j] = MOVE_NONE;
 
     if(Threads[threadID].printCurrentLine)
       print_current_line(ss, ply, threadID);
@@ -2014,14 +2051,32 @@ namespace {
   }
 
 
+  // move_is_killer() checks if the given move is among the
+  // killer moves of that ply.
+
+  bool move_is_killer(Move m, const SearchStack& ss) {
+
+      const Move* k = ss.killers;
+      for (int i = 0; i < KILLER_MAX; i++, k++)
+          if (*k == m)
+              return true;
+
+      return false;
+  }
+
+
   // extension() decides whether a move should be searched with normal depth,
   // or with extended depth.  Certain classes of moves (checking moves, in
-  // particular) are searched with bigger depth than ordinary moves.
+  // particular) are searched with bigger depth than ordinary moves and in
+  // any case are marked as 'dangerous'. Note that also if a move is not
+  // extended, as example because the corresponding UCI option is set to zero,
+  // the move is marked as 'dangerous' so, at least, we avoid to prune it.
 
-  Depth extension(const Position &pos, Move m, bool pvNode,
-                  bool check, bool singleReply, bool mateThreat) {
+  Depth extension(const Position &pos, Move m, bool pvNode, bool check,
+                  bool singleReply, bool mateThreat, bool* dangerous) {
 
     Depth result = Depth(0);
+    *dangerous = check || singleReply || mateThreat;
 
     if (check)
         result += CheckExtension[pvNode];
@@ -2029,26 +2084,37 @@ namespace {
     if (singleReply)
         result += SingleReplyExtension[pvNode];
 
-    if (pos.move_is_pawn_push_to_7th(m))
-        result += PawnPushTo7thExtension[pvNode];
-
-    if (pos.move_is_passed_pawn_push(m))
-        result += PassedPawnExtension[pvNode];
-
     if (mateThreat)
         result += MateThreatExtension[pvNode];
 
-    if (   pos.midgame_value_of_piece_on(move_to(m)) >= RookValueMidgame
-        && (  pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
-            - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
+    if (pos.move_is_pawn_push_to_7th(m))
+    {
+        result += PawnPushTo7thExtension[pvNode];
+        *dangerous = true;
+    }
+    if (pos.move_is_passed_pawn_push(m))
+    {
+        result += PassedPawnExtension[pvNode];
+        *dangerous = true;
+    }
+
+    if (   pos.midgame_value_of_piece_on(move_to(m)) >= RookValueMidgame
+        && (  pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
+            - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
         && !move_promotion(m))
+    {
         result += PawnEndgameExtension[pvNode];
-    
+        *dangerous = true;
+    }
+
     if (   pvNode
         && pos.move_is_capture(m)
         && pos.type_of_piece_on(move_to(m)) != PAWN
         && pos.see(m) >= 0)
+    {
         result += OnePly/2;
+        *dangerous = true;
+    }
 
     return Min(result, OnePly);
   }
@@ -2137,13 +2203,11 @@ namespace {
 
 
   // ok_to_history() returns true if a move m can be stored
-  // in history. Should be a non capturing move.
+  // in history. Should be a non capturing move nor a promotion.
 
   bool ok_to_history(const Position& pos, Move m) {
 
-    return    pos.square_is_empty(move_to(m))
-          && !move_promotion(m)
-          && !move_is_ep(m);
+    return !pos.move_is_capture(m) && !move_promotion(m);
   }
 
 
@@ -2156,8 +2220,26 @@ namespace {
     H.success(pos.piece_on(move_from(m)), m, depth);
 
     for (int i = 0; i < moveCount - 1; i++)
-        if (ok_to_history(pos, movesSearched[i]) && m != movesSearched[i])
+    {
+        assert(m != movesSearched[i]);
+        if (ok_to_history(pos, movesSearched[i]))
             H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
+    }
+  }
+
+
+  // update_killers() add a good move that produced a beta-cutoff
+  // among the killer moves of that ply.
+
+  void update_killers(Move m, SearchStack& ss) {
+
+    if (m == ss.killers[0])
+        return;
+
+    for (int i = KILLER_MAX - 1; i > 0; i--)
+        ss.killers[i] = ss.killers[i - 1];
+
+    ss.killers[0] = m;
   }
 
   // fail_high_ply_1() checks if some thread is currently resolving a fail

src/search.h

@@ -41,6 +41,7 @@
 
 const int PLY_MAX = 100;
 const int PLY_MAX_PLUS_2 = 102;
+const int KILLER_MAX = 2;
 
 
 ////
@@ -56,8 +57,9 @@ struct SearchStack {
   Move pv[PLY_MAX];
   Move currentMove;
   Value currentMoveCaptureValue;
-  Move mateKiller, killer1, killer2;
+  Move mateKiller;
   Move threatMove;
+  Move killers[KILLER_MAX];
   Depth reduction;
 };
 
@@ -66,10 +68,9 @@ struct SearchStack {
 //// Global variables
 ////
 
+extern SearchStack EmptySearchStack;
 extern TranspositionTable TT;
-
 extern int ActiveThreads;
-
 extern Lock SMPLock;
 
 // Perhaps better to make H local, and pass as parameter to MovePicker?

src/square.h

@@ -25,6 +25,7 @@
 //// Includes
 ////
 
+#include <cstdlib> // for abs()
 #include <string>
 
 #include "color.h"

src/tt.cpp

@@ -24,6 +24,7 @@
 
 #include <cassert>
 #include <cmath>
+#include <cstring>
 
 #include "tt.h"
 
@@ -107,29 +108,25 @@ void TranspositionTable::store(const Position &pos, Value v, Depth d,
   TTEntry *tte, *replace;
 
   tte = replace = first_entry(pos);
-  for (int i = 0; i < 4; i++)
+  for (int i = 0; i < 4; i++, tte++)
   {
-    if (!(tte+i)->key()) // still empty
-    {
-        *(tte+i) = TTEntry(pos.get_key(), v, type, d, m, generation);
-        writes++;
-        return;
-    }
-    if ((tte+i)->key() == pos.get_key()) // overwrite old
+    if (!tte->key() || tte->key() == pos.get_key()) // empty or overwrite old
     {
         if (m == MOVE_NONE)
-            m = (tte+i)->move();
+            m = tte->move();
 
-        *(tte+i) = TTEntry(pos.get_key(), v, type, d, m, generation);
+        *tte = TTEntry(pos.get_key(), v, type, d, m, generation);
         return;
     }
-    if (   i == 0  // already is (replace == tte+i), common case
-        || replace->generation() < (tte+i)->generation())
+    else if (i == 0)  // replace would be a no-op in this common case
         continue;
 
-    if (    replace->generation() > (tte+i)->generation()
-        || (tte+i)->depth() < replace->depth())
-        replace = tte+i;
+    int c1 = (replace->generation() == generation ?  2 : 0);
+    int c2 = (tte->generation() == generation ? -2 : 0);
+    int c3 = (tte->depth() < replace->depth() ?  1 : 0);
+
+    if (c1 + c2 + c3 > 0)
+        replace = tte;
   }
   *replace = TTEntry(pos.get_key(), v, type, d, m, generation);
   writes++;
@@ -144,9 +141,8 @@ const TTEntry* TranspositionTable::retrieve(const Position &pos) const {
 
   TTEntry *tte = first_entry(pos);
 
-  for (int i = 0; i < 4; i++)
+  for (int i = 0; i < 4; i++, tte++)
   {
-      tte += i;
       if (tte->key() == pos.get_key())
           return tte;
   }

src/ucioption.cpp

@@ -120,6 +120,7 @@ namespace {
     o.push_back(Option("Full Depth Moves (non-PV nodes)", 3, 1, 100));
     o.push_back(Option("Threat Depth", 5, 0, 100));
     o.push_back(Option("Selective Plies", 7, 0, 10));
+    o.push_back(Option("Null driven IID", true));
     o.push_back(Option("Futility Pruning (Main Search)", true));
     o.push_back(Option("Futility Pruning (Quiescence Search)", true));
     o.push_back(Option("Futility Margin 0", 50, 0, 1000));
@@ -176,7 +177,7 @@ namespace {
   template<typename T>
   T get_option_value(const std::string& optionName) {
 
-      T ret;
+      T ret = T();
       Options::iterator it = option_with_name(optionName);
 
       if (it != options.end())