Bishop pins only

src/endgame.cpp

@@ -471,6 +471,29 @@ ScaleFactor Endgame<KBPsK>::operator()(const Position& pos) const {
               return SCALE_FACTOR_DRAW;
       }
   }
+
+  // All pawns on same B or G file? Then potential draw
+  if (    (pawnFile == FILE_B || pawnFile == FILE_G)
+      && !(pos.pieces(PAWN) & ~file_bb(pawnFile))
+      && pos.non_pawn_material(weakerSide) == 0
+      && pos.piece_count(weakerSide, PAWN) >= 1)
+  {
+      // Get weaker pawn closest to opponent's queening square
+      Bitboard wkPawns = pos.pieces(weakerSide, PAWN);
+      Square weakerPawnSq = strongerSide == WHITE ? msb(wkPawns) : lsb(wkPawns);
+
+      Square strongerKingSq = pos.king_square(strongerSide);
+      Square weakerKingSq = pos.king_square(weakerSide);
+      Square bishopSq = pos.piece_list(strongerSide, BISHOP)[0];
+
+      // Draw if weaker pawn is on rank 7, bishop can't attack the pawn, and
+      // weaker king can stop opposing opponent's king from penetrating.
+      if (   relative_rank(strongerSide, weakerPawnSq) == RANK_7
+          && opposite_colors(bishopSq, weakerPawnSq)
+          && square_distance(weakerPawnSq, weakerKingSq) <= square_distance(weakerPawnSq, strongerKingSq))
+          return SCALE_FACTOR_DRAW;
+  }
+
   return SCALE_FACTOR_NONE;
 }
 

src/evaluate.cpp

@@ -577,16 +577,15 @@ Value do_evaluate(const Position& pos, Value& margin) {
 
         mobility += MobilityBonus[Piece][mob];
 
-        if (Piece == BISHOP && (PseudoAttacks[Piece][pos.king_square(Them)] & s)) {
-             const Bitboard between = BetweenBB[s][pos.king_square(Them)] & pos.pieces();
-             if (!more_than_one(between))
-                 score += make_score(25, 25);
-        }
-
         // Decrease score if we are attacked by an enemy pawn. Remaining part
         // of threat evaluation must be done later when we have full attack info.
         if (ei.attackedBy[Them][PAWN] & s)
             score -= ThreatenedByPawnPenalty[Piece];
+        else if (Piece == BISHOP && (PseudoAttacks[Piece][pos.king_square(Them)] & s)) {
+             const Bitboard between = BetweenBB[s][pos.king_square(Them)] & pos.pieces();
+             if (!more_than_one(between))
+                 score += make_score(15, 25);
+        }
 
         // Bishop and knight outposts squares
         if (    (Piece == BISHOP || Piece == KNIGHT)
@@ -693,7 +692,8 @@ Value do_evaluate(const Position& pos, Value& margin) {
                       & ~ei.attackedBy[Them][0];
 
     if (undefendedMinors)
-        score += UndefendedMinorPenalty;
+        score += more_than_one(undefendedMinors) ? UndefendedMinorPenalty * 2
+                                                 : UndefendedMinorPenalty;
 
     // Enemy pieces not defended by a pawn and under our attack
     weakEnemies =  pos.pieces(Them)

src/history.h

@@ -1,72 +0,0 @@
-/*
-  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
-  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
-  Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
-
-  Stockfish is free software: you can redistribute it and/or modify
-  it under the terms of the GNU General Public License as published by
-  the Free Software Foundation, either version 3 of the License, or
-  (at your option) any later version.
-
-  Stockfish is distributed in the hope that it will be useful,
-  but WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-  GNU General Public License for more details.
-
-  You should have received a copy of the GNU General Public License
-  along with this program.  If not, see <http://www.gnu.org/licenses/>.
-*/
-
-#if !defined(HISTORY_H_INCLUDED)
-#define HISTORY_H_INCLUDED
-
-#include <algorithm>
-#include <cstring>
-
-#include "types.h"
-
-/// The History class stores statistics about how often different moves
-/// have been successful or unsuccessful during the current search. These
-/// statistics are used for reduction and move ordering decisions. History
-/// entries are stored according only to moving piece and destination square,
-/// in particular two moves with different origin but same destination and
-/// same piece will be considered identical.
-
-class History {
-
-public:
-  void clear();
-  Value value(Piece p, Square to) const;
-  void add(Piece p, Square to, Value bonus);
-  Value gain(Piece p, Square to) const;
-  void update_gain(Piece p, Square to, Value g);
-
-  static const Value MaxValue = Value(2000);
-
-private:
-  Value history[PIECE_NB][SQUARE_NB];
-  Value maxGains[PIECE_NB][SQUARE_NB];
-};
-
-inline void History::clear() {
-  memset(history,  0, 16 * 64 * sizeof(Value));
-  memset(maxGains, 0, 16 * 64 * sizeof(Value));
-}
-
-inline Value History::value(Piece p, Square to) const {
-  return history[p][to];
-}
-
-inline void History::add(Piece p, Square to, Value bonus) {
-  if (abs(history[p][to] + bonus) < MaxValue) history[p][to] += bonus;
-}
-
-inline Value History::gain(Piece p, Square to) const {
-  return maxGains[p][to];
-}
-
-inline void History::update_gain(Piece p, Square to, Value g) {
-  maxGains[p][to] = std::max(g, maxGains[p][to] - 1);
-}
-
-#endif // !defined(HISTORY_H_INCLUDED)

src/movegen.cpp

@@ -249,41 +249,38 @@ namespace {
   }
 
 
-  FORCE_INLINE MoveStack* generate_king_moves(const Position& pos, MoveStack* mlist,
-                                              Color us, Bitboard target) {
-    Square from = pos.king_square(us);
-    Bitboard b = pos.attacks_from<KING>(from) & target;
-    SERIALIZE(b);
-    return mlist;
-  }
-
-
   template<GenType Type> FORCE_INLINE
-  MoveStack* generate_all_moves(const Position& pos, MoveStack* mlist, Color us,
+  MoveStack* generate_all(const Position& pos, MoveStack* mlist, Color us,
-                                Bitboard target, const CheckInfo* ci = NULL) {
+                          Bitboard target, const CheckInfo* ci = NULL) {
+
+    const bool Checks = Type == QUIET_CHECKS;
 
     mlist = (us == WHITE ? generate_pawn_moves<WHITE, Type>(pos, mlist, target, ci)
                          : generate_pawn_moves<BLACK, Type>(pos, mlist, target, ci));
 
-    mlist = generate_moves<KNIGHT, Type == QUIET_CHECKS>(pos, mlist, us, target, ci);
+    mlist = generate_moves<KNIGHT, Checks>(pos, mlist, us, target, ci);
-    mlist = generate_moves<BISHOP, Type == QUIET_CHECKS>(pos, mlist, us, target, ci);
+    mlist = generate_moves<BISHOP, Checks>(pos, mlist, us, target, ci);
-    mlist = generate_moves<ROOK,   Type == QUIET_CHECKS>(pos, mlist, us, target, ci);
+    mlist = generate_moves<ROOK,   Checks>(pos, mlist, us, target, ci);
-    mlist = generate_moves<QUEEN,  Type == QUIET_CHECKS>(pos, mlist, us, target, ci);
+    mlist = generate_moves<QUEEN,  Checks>(pos, mlist, us, target, ci);
 
     if (Type != QUIET_CHECKS && Type != EVASIONS)
-        mlist = generate_king_moves(pos, mlist, us, target);
+    {
+        Square from = pos.king_square(us);
+        Bitboard b = pos.attacks_from<KING>(from) & target;
+        SERIALIZE(b);
+    }
 
     if (Type != CAPTURES && Type != EVASIONS && pos.can_castle(us))
     {
         if (pos.is_chess960())
         {
-            mlist = generate_castle<KING_SIDE,  Type == QUIET_CHECKS, true>(pos, mlist, us);
+            mlist = generate_castle<KING_SIDE,  Checks, true>(pos, mlist, us);
-            mlist = generate_castle<QUEEN_SIDE, Type == QUIET_CHECKS, true>(pos, mlist, us);
+            mlist = generate_castle<QUEEN_SIDE, Checks, true>(pos, mlist, us);
         }
         else
         {
-            mlist = generate_castle<KING_SIDE,  Type == QUIET_CHECKS, false>(pos, mlist, us);
+            mlist = generate_castle<KING_SIDE,  Checks, false>(pos, mlist, us);
-            mlist = generate_castle<QUEEN_SIDE, Type == QUIET_CHECKS, false>(pos, mlist, us);
+            mlist = generate_castle<QUEEN_SIDE, Checks, false>(pos, mlist, us);
         }
     }
 
@@ -310,18 +307,12 @@ MoveStack* generate(const Position& pos, MoveStack* mlist) {
   assert(!pos.checkers());
 
   Color us = pos.side_to_move();
-  Bitboard target;
 
-  if (Type == CAPTURES)
+  Bitboard target = Type == CAPTURES     ?  pos.pieces(~us)
-      target = pos.pieces(~us);
+                  : Type == QUIETS       ? ~pos.pieces()
+                  : Type == NON_EVASIONS ? ~pos.pieces(us) : 0;
 
-  else if (Type == QUIETS)
+  return generate_all<Type>(pos, mlist, us, target);
-      target = ~pos.pieces();
-
-  else if (Type == NON_EVASIONS)
-      target = ~pos.pieces(us);
-
-  return generate_all_moves<Type>(pos, mlist, us, target);
 }
 
 // Explicit template instantiations
@@ -337,7 +328,6 @@ MoveStack* generate<QUIET_CHECKS>(const Position& pos, MoveStack* mlist) {
 
   assert(!pos.checkers());
 
-  Color us = pos.side_to_move();
   CheckInfo ci(pos);
   Bitboard dc = ci.dcCandidates;
 
@@ -357,7 +347,7 @@ MoveStack* generate<QUIET_CHECKS>(const Position& pos, MoveStack* mlist) {
      SERIALIZE(b);
   }
 
-  return generate_all_moves<QUIET_CHECKS>(pos, mlist, us, ~pos.pieces(), &ci);
+  return generate_all<QUIET_CHECKS>(pos, mlist, pos.side_to_move(), ~pos.pieces(), &ci);
 }
 
 
@@ -419,7 +409,7 @@ MoveStack* generate<EVASIONS>(const Position& pos, MoveStack* mlist) {
   // Generate blocking evasions or captures of the checking piece
   Bitboard target = between_bb(checksq, ksq) | pos.checkers();
 
-  return generate_all_moves<EVASIONS>(pos, mlist, us, target);
+  return generate_all<EVASIONS>(pos, mlist, us, target);
 }
 
 

src/movepick.cpp

@@ -18,10 +18,8 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include <algorithm>
 #include <cassert>
 
-#include "movegen.h"
 #include "movepick.h"
 #include "thread.h"
 
@@ -37,6 +35,20 @@ namespace {
     STOP
   };
 
+  // Our insertion sort, guaranteed to be stable, as is needed
+  void insertion_sort(MoveStack* begin, MoveStack* end)
+  {
+    MoveStack tmp, *p, *q;
+
+    for (p = begin + 1; p < end; ++p)
+    {
+        tmp = *p;
+        for (q = p; q != begin && *(q-1) < tmp; --q)
+            *q = *(q-1);
+        *q = tmp;
+    }
+  }
+
   // Unary predicate used by std::partition to split positive scores from remaining
   // ones so to sort separately the two sets, and with the second sort delayed.
   inline bool has_positive_score(const MoveStack& ms) { return ms.score > 0; }
@@ -59,7 +71,7 @@ namespace {
 /// move ordering is at the current node.
 
 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const History& h,
-                       Search::Stack* s, Value beta) : pos(p), H(h), depth(d) {
+                       Search::Stack* s, Value beta) : pos(p), Hist(h), depth(d) {
 
   assert(d > DEPTH_ZERO);
 
@@ -92,7 +104,7 @@ MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const History& h,
 }
 
 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const History& h,
-                       Square sq) : pos(p), H(h), cur(moves), end(moves) {
+                       Square sq) : pos(p), Hist(h), cur(moves), end(moves) {
 
   assert(d <= DEPTH_ZERO);
 
@@ -124,7 +136,7 @@ MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const History& h,
 }
 
 MovePicker::MovePicker(const Position& p, Move ttm, const History& h, PieceType pt)
-                       : pos(p), H(h), cur(moves), end(moves) {
+                       : pos(p), Hist(h), cur(moves), end(moves) {
 
   assert(!pos.checkers());
 
@@ -141,12 +153,10 @@ MovePicker::MovePicker(const Position& p, Move ttm, const History& h, PieceType
 }
 
 
-/// MovePicker::score_captures(), MovePicker::score_noncaptures() and
+/// score() assign a numerical move ordering score to each move in a move list.
-/// MovePicker::score_evasions() assign a numerical move ordering score
+/// The moves with highest scores will be picked first.
-/// to each move in a move list.  The moves with highest scores will be
+template<>
-/// picked first by next_move().
+void MovePicker::score<CAPTURES>() {
-
-void MovePicker::score_captures() {
   // Winning and equal captures in the main search are ordered by MVV/LVA.
   // Suprisingly, this appears to perform slightly better than SEE based
   // move ordering. The reason is probably that in a position with a winning
@@ -169,47 +179,50 @@ void MovePicker::score_captures() {
                  - type_of(pos.piece_moved(m));
 
       if (type_of(m) == PROMOTION)
-          it->score += PieceValue[MG][promotion_type(m)];
+          it->score += PieceValue[MG][promotion_type(m)] - PieceValue[MG][PAWN];
+
+      else if (type_of(m) == ENPASSANT)
+          it->score += PieceValue[MG][PAWN];
   }
 }
 
-void MovePicker::score_noncaptures() {
+template<>
+void MovePicker::score<QUIETS>() {
 
   Move m;
 
   for (MoveStack* it = moves; it != end; ++it)
   {
       m = it->move;
-      it->score = H.value(pos.piece_moved(m), to_sq(m));
+      it->score = Hist[pos.piece_moved(m)][to_sq(m)];
   }
 }
 
-void MovePicker::score_evasions() {
+template<>
+void MovePicker::score<EVASIONS>() {
   // Try good captures ordered by MVV/LVA, then non-captures if destination square
   // is not under attack, ordered by history value, then bad-captures and quiet
   // moves with a negative SEE. This last group is ordered by the SEE score.
   Move m;
   int seeScore;
 
-  if (end < moves + 2)
-      return;
-
   for (MoveStack* it = moves; it != end; ++it)
   {
       m = it->move;
       if ((seeScore = pos.see_sign(m)) < 0)
-          it->score = seeScore - History::MaxValue; // Be sure we are at the bottom
+          it->score = seeScore - History::Max; // At the bottom
+
       else if (pos.is_capture(m))
           it->score =  PieceValue[MG][pos.piece_on(to_sq(m))]
-                     - type_of(pos.piece_moved(m)) + History::MaxValue;
+                     - type_of(pos.piece_moved(m)) + History::Max;
       else
-          it->score = H.value(pos.piece_moved(m), to_sq(m));
+          it->score = Hist[pos.piece_moved(m)][to_sq(m)];
   }
 }
 
 
-/// MovePicker::generate_next() generates, scores and sorts the next bunch of moves,
+/// generate_next() generates, scores and sorts the next bunch of moves, when
-/// when there are no more moves to try for the current phase.
+/// there are no more moves to try for the current phase.
 
 void MovePicker::generate_next() {
 
@@ -219,7 +232,7 @@ void MovePicker::generate_next() {
 
   case CAPTURES_S1: case CAPTURES_S3: case CAPTURES_S4: case CAPTURES_S5: case CAPTURES_S6:
       end = generate<CAPTURES>(pos, moves);
-      score_captures();
+      score<CAPTURES>();
       return;
 
   case KILLERS_S1:
@@ -229,16 +242,16 @@ void MovePicker::generate_next() {
 
   case QUIETS_1_S1:
       endQuiets = end = generate<QUIETS>(pos, moves);
-      score_noncaptures();
+      score<QUIETS>();
       end = std::partition(cur, end, has_positive_score);
-      sort<MoveStack>(cur, end);
+      insertion_sort(cur, end);
       return;
 
   case QUIETS_2_S1:
       cur = end;
       end = endQuiets;
       if (depth >= 3 * ONE_PLY)
-          sort<MoveStack>(cur, end);
+          insertion_sort(cur, end);
       return;
 
   case BAD_CAPTURES_S1:
@@ -249,7 +262,8 @@ void MovePicker::generate_next() {
 
   case EVASIONS_S2:
       end = generate<EVASIONS>(pos, moves);
-      score_evasions();
+      if (end > moves + 1)
+          score<EVASIONS>();
       return;
 
   case QUIET_CHECKS_S3:
@@ -268,11 +282,10 @@ void MovePicker::generate_next() {
 }
 
 
-/// MovePicker::next_move() is the most important method of the MovePicker class.
+/// next_move() is the most important method of the MovePicker class. It returns
-/// It returns a new pseudo legal move every time it is called, until there
+/// a new pseudo legal move every time is called, until there are no more moves
-/// are no more moves left. It picks the move with the biggest score from a list
+/// left. It picks the move with the biggest score from a list of generated moves
-/// of generated moves taking care not to return the tt move if has already been
+/// taking care not returning the ttMove if has already been searched previously.
-/// searched previously.
 template<>
 Move MovePicker::next_move<false>() {
 
@@ -359,6 +372,6 @@ Move MovePicker::next_move<false>() {
 
 /// Version of next_move() to use at split point nodes where the move is grabbed
 /// from the split point's shared MovePicker object. This function is not thread
-/// safe so should be lock protected by the caller.
+/// safe so must be lock protected by the caller.
 template<>
-Move MovePicker::next_move<true>() { return ss->sp->mp->next_move<false>(); }
+Move MovePicker::next_move<true>() { return ss->sp->movePicker->next_move<false>(); }

src/movepick.h

@@ -20,12 +20,48 @@
 #if !defined MOVEPICK_H_INCLUDED
 #define MOVEPICK_H_INCLUDED
 
-#include "history.h"
+#include <algorithm> // For std::max
+#include <cstring>   // For memset
+
+#include "movegen.h"
 #include "position.h"
 #include "search.h"
 #include "types.h"
 
 
+/// The Stats struct stores moves statistics. According to the template parameter
+/// the class can store both History and Gains type statistics. History records
+/// how often different moves have been successful or unsuccessful during the
+/// current search and is used for reduction and move ordering decisions. Gains
+/// records the move's best evaluation gain from one ply to the next and is used
+/// for pruning decisions. Entries are stored according only to moving piece and
+/// destination square, in particular two moves with different origin but same
+/// destination and same piece will be considered identical.
+template<bool Gain>
+struct Stats {
+
+  static const Value Max = Value(2000);
+
+  const Value* operator[](Piece p) const { return &table[p][0]; }
+  void clear() { memset(table, 0, sizeof(table)); }
+
+  void update(Piece p, Square to, Value v) {
+
+    if (Gain)
+        table[p][to] = std::max(v, table[p][to] - 1);
+
+    else if (abs(table[p][to] + v) < Max)
+        table[p][to] +=  v;
+  }
+
+private:
+  Value table[PIECE_NB][SQUARE_NB];
+};
+
+typedef Stats<false> History;
+typedef Stats<true> Gains;
+
+
 /// MovePicker class is used to pick one pseudo legal move at a time from the
 /// current position. The most important method is next_move(), which returns a
 /// new pseudo legal move each time it is called, until there are no moves left,
@@ -44,13 +80,11 @@ public:
   template<bool SpNode> Move next_move();
 
 private:
-  void score_captures();
+  template<GenType> void score();
-  void score_noncaptures();
-  void score_evasions();
   void generate_next();
 
   const Position& pos;
-  const History& H;
+  const History& Hist;
   Search::Stack* ss;
   Depth depth;
   Move ttMove;

src/notation.cpp

@@ -110,8 +110,7 @@ const string move_to_san(Position& pos, Move m) {
 
   assert(MoveList<LEGAL>(pos).contains(m));
 
-  Bitboard attackers;
+  Bitboard others, b;
-  bool ambiguousMove, ambiguousFile, ambiguousRank;
   string san;
   Color us = pos.side_to_move();
   Square from = from_sq(m);
@@ -127,31 +126,23 @@ const string move_to_san(Position& pos, Move m) {
       {
           san = PieceToChar[WHITE][pt]; // Upper case
 
-          // Disambiguation if we have more then one piece with destination 'to'
+          // Disambiguation if we have more then one piece of type 'pt' that can
-          // note that for pawns is not needed because starting file is explicit.
+          // reach 'to' with a legal move.
-          ambiguousMove = ambiguousFile = ambiguousRank = false;
+          others = b = (pos.attacks_from(pc, to) & pos.pieces(us, pt)) ^ from;
 
-          attackers = (pos.attacks_from(pc, to) & pos.pieces(us, pt)) ^ from;
+          while (b)
-
-          while (attackers)
           {
-              Square sq = pop_lsb(&attackers);
+              Move move = make_move(pop_lsb(&b), to);
-
+              if (!pos.pl_move_is_legal(move, pos.pinned_pieces()))
-              // If the move is illegal, the piece is not included in the sub-set
+                  others ^= from_sq(move);
-              if (!pos.pl_move_is_legal(make_move(sq, to), pos.pinned_pieces()))
-                  continue;
-
-              ambiguousFile |= file_of(sq) == file_of(from);
-              ambiguousRank |= rank_of(sq) == rank_of(from);
-              ambiguousMove = true;
           }
 
-          if (ambiguousMove)
+          if (others)
           {
-              if (!ambiguousFile)
+              if (!(others & file_bb(from)))
                   san += file_to_char(file_of(from));
 
-              else if (!ambiguousRank)
+              else if (!(others & rank_bb(from)))
                   san += rank_to_char(rank_of(from));
 
               else

src/position.cpp

@@ -740,13 +740,6 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
   st->rule50++;
   st->pliesFromNull++;
 
-  if (type_of(m) == CASTLE)
-  {
-      st->key = k;
-      do_castle_move<true>(m);
-      return;
-  }
-
   Color us = sideToMove;
   Color them = ~us;
   Square from = from_sq(m);
@@ -756,9 +749,25 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
   PieceType capture = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));
 
   assert(color_of(piece) == us);
-  assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them);
+  assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them || type_of(m) == CASTLE);
   assert(capture != KING);
 
+  if (type_of(m) == CASTLE)
+  {
+      assert(piece == make_piece(us, KING));
+
+      bool kingSide = to > from;
+      Square rfrom = to; // Castle is encoded as "king captures friendly rook"
+      Square rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
+      to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
+      capture = NO_PIECE_TYPE;
+
+      do_castle(from, to, rfrom, rto);
+
+      st->psqScore += psq_delta(make_piece(us, ROOK), rfrom, rto);
+      k ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
+  }
+
   if (capture)
   {
       Square capsq = to;
@@ -793,7 +802,7 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
       // Update piece list, move the last piece at index[capsq] position and
       // shrink the list.
       //
-      // WARNING: This is a not revresible operation. When we will reinsert the
+      // WARNING: This is a not reversible operation. When we will reinsert the
       // captured piece in undo_move() we will put it at the end of the list and
       // not in its original place, it means index[] and pieceList[] are not
       // guaranteed to be invariant to a do_move() + undo_move() sequence.
@@ -802,9 +811,10 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
       pieceList[them][capture][index[lastSquare]] = lastSquare;
       pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
 
-      // Update hash keys
+      // Update material hash key and prefetch access to materialTable
       k ^= Zobrist::psq[them][capture][capsq];
       st->materialKey ^= Zobrist::psq[them][capture][pieceCount[them][capture]];
+      prefetch((char*)thisThread->materialTable[st->materialKey]);
 
       // Update incremental scores
       st->psqScore -= pieceSquareTable[make_piece(them, capture)][capsq];
@@ -831,22 +841,25 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
       st->castleRights &= ~cr;
   }
 
-  // Prefetch TT access as soon as we know key is updated
+  // Prefetch TT access as soon as we know the new hash key
   prefetch((char*)TT.first_entry(k));
 
-  // Move the piece
+  // Move the piece. The tricky Chess960 castle is handled earlier
-  Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
+  if (type_of(m) != CASTLE)
-  byTypeBB[ALL_PIECES] ^= from_to_bb;
+  {
-  byTypeBB[pt] ^= from_to_bb;
+      Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
-  byColorBB[us] ^= from_to_bb;
+      byTypeBB[ALL_PIECES] ^= from_to_bb;
+      byTypeBB[pt] ^= from_to_bb;
+      byColorBB[us] ^= from_to_bb;
 
-  board[to] = board[from];
+      board[from] = NO_PIECE;
-  board[from] = NO_PIECE;
+      board[to] = piece;
 
-  // Update piece lists, index[from] is not updated and becomes stale. This
+      // Update piece lists, index[from] is not updated and becomes stale. This
-  // works as long as index[] is accessed just by known occupied squares.
+      // works as long as index[] is accessed just by known occupied squares.
-  index[to] = index[from];
+      index[to] = index[from];
-  pieceList[us][pt][index[to]] = to;
+      pieceList[us][pt][index[to]] = to;
+  }
 
   // If the moving piece is a pawn do some special extra work
   if (pt == PAWN)
@@ -894,17 +907,14 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
           st->npMaterial[us] += PieceValue[MG][promotion];
       }
 
-      // Update pawn hash key
+      // Update pawn hash key and prefetch access to pawnsTable
       st->pawnKey ^= Zobrist::psq[us][PAWN][from] ^ Zobrist::psq[us][PAWN][to];
+      prefetch((char*)thisThread->pawnsTable[st->pawnKey]);
 
       // Reset rule 50 draw counter
       st->rule50 = 0;
   }
 
-  // Prefetch pawn and material hash tables
-  prefetch((char*)thisThread->pawnsTable[st->pawnKey]);
-  prefetch((char*)thisThread->materialTable[st->materialKey]);
-
   // Update incremental scores
   st->psqScore += psq_delta(piece, from, to);
 
@@ -954,22 +964,14 @@ void Position::undo_move(Move m) {
 
   sideToMove = ~sideToMove;
 
-  if (type_of(m) == CASTLE)
-  {
-      do_castle_move<false>(m);
-      return;
-  }
-
   Color us = sideToMove;
   Color them = ~us;
   Square from = from_sq(m);
   Square to = to_sq(m);
-  Piece piece = piece_on(to);
+  PieceType pt = type_of(piece_on(to));
-  PieceType pt = type_of(piece);
   PieceType capture = st->capturedType;
 
-  assert(is_empty(from));
+  assert(is_empty(from) || type_of(m) == CASTLE);
-  assert(color_of(piece) == us);
   assert(capture != KING);
 
   if (type_of(m) == PROMOTION)
@@ -997,19 +999,32 @@ void Position::undo_move(Move m) {
       pt = PAWN;
   }
 
-  // Put the piece back at the source square
+  if (type_of(m) == CASTLE)
-  Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
+  {
-  byTypeBB[ALL_PIECES] ^= from_to_bb;
+      bool kingSide = to > from;
-  byTypeBB[pt] ^= from_to_bb;
+      Square rfrom = to; // Castle is encoded as "king captures friendly rook"
-  byColorBB[us] ^= from_to_bb;
+      Square rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
+      to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
+      capture = NO_PIECE_TYPE;
+      pt = KING;
+      do_castle(to, from, rto, rfrom);
+  }
+  else
+  {
+      // Put the piece back at the source square
+      Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
+      byTypeBB[ALL_PIECES] ^= from_to_bb;
+      byTypeBB[pt] ^= from_to_bb;
+      byColorBB[us] ^= from_to_bb;
 
-  board[from] = board[to];
+      board[to] = NO_PIECE;
-  board[to] = NO_PIECE;
+      board[from] = make_piece(us, pt);
 
-  // Update piece lists, index[to] is not updated and becomes stale. This
+      // Update piece lists, index[to] is not updated and becomes stale. This
-  // works as long as index[] is accessed just by known occupied squares.
+      // works as long as index[] is accessed just by known occupied squares.
-  index[from] = index[to];
+      index[from] = index[to];
-  pieceList[us][pt][index[from]] = from;
+      pieceList[us][pt][index[from]] = from;
+  }
 
   if (capture)
   {
@@ -1044,44 +1059,12 @@ void Position::undo_move(Move m) {
 }
 
 
-/// Position::do_castle_move() is a private method used to do/undo a castling
+/// Position::do_castle() is a helper used to do/undo a castling move. This
-/// move. Note that castling moves are encoded as "king captures friendly rook"
+/// is a bit tricky, especially in Chess960.
-/// moves, for instance white short castling in a non-Chess960 game is encoded
-/// as e1h1.
-template<bool Do>
-void Position::do_castle_move(Move m) {
 
-  assert(is_ok(m));
+void Position::do_castle(Square kfrom, Square kto, Square rfrom, Square rto) {
-  assert(type_of(m) == CASTLE);
-
-  Square kto, kfrom, rfrom, rto, kAfter, rAfter;
 
   Color us = sideToMove;
-  Square kBefore = from_sq(m);
-  Square rBefore = to_sq(m);
-
-  // Find after-castle squares for king and rook
-  if (rBefore > kBefore) // O-O
-  {
-      kAfter = relative_square(us, SQ_G1);
-      rAfter = relative_square(us, SQ_F1);
-  }
-  else // O-O-O
-  {
-      kAfter = relative_square(us, SQ_C1);
-      rAfter = relative_square(us, SQ_D1);
-  }
-
-  kfrom = Do ? kBefore : kAfter;
-  rfrom = Do ? rBefore : rAfter;
-
-  kto = Do ? kAfter : kBefore;
-  rto = Do ? rAfter : rBefore;
-
-  assert(piece_on(kfrom) == make_piece(us, KING));
-  assert(piece_on(rfrom) == make_piece(us, ROOK));
-
-  // Move the pieces, with some care; in chess960 could be kto == rfrom
   Bitboard k_from_to_bb = SquareBB[kfrom] ^ SquareBB[kto];
   Bitboard r_from_to_bb = SquareBB[rfrom] ^ SquareBB[rto];
   byTypeBB[KING] ^= k_from_to_bb;
@@ -1089,98 +1072,56 @@ void Position::do_castle_move(Move m) {
   byTypeBB[ALL_PIECES] ^= k_from_to_bb ^ r_from_to_bb;
   byColorBB[us] ^= k_from_to_bb ^ r_from_to_bb;
 
-  // Update board
+  // Could be from == to, so first set NO_PIECE then KING and ROOK
-  Piece king = make_piece(us, KING);
-  Piece rook = make_piece(us, ROOK);
   board[kfrom] = board[rfrom] = NO_PIECE;
-  board[kto] = king;
+  board[kto] = make_piece(us, KING);
-  board[rto] = rook;
+  board[rto] = make_piece(us, ROOK);
 
-  // Update piece lists
+  // Could be kfrom == rto, so use a 'tmp' variable
-  pieceList[us][KING][index[kfrom]] = kto;
+  int tmp = index[kfrom];
-  pieceList[us][ROOK][index[rfrom]] = rto;
+  index[rto] = index[rfrom];
-  int tmp = index[rfrom]; // In Chess960 could be kto == rfrom
+  index[kto] = tmp;
-  index[kto] = index[kfrom];
+  pieceList[us][KING][index[kto]] = kto;
-  index[rto] = tmp;
+  pieceList[us][ROOK][index[rto]] = rto;
-
-  if (Do)
-  {
-      // Reset capture field
-      st->capturedType = NO_PIECE_TYPE;
-
-      // Update incremental scores
-      st->psqScore += psq_delta(king, kfrom, kto);
-      st->psqScore += psq_delta(rook, rfrom, rto);
-
-      // Update hash key
-      st->key ^= Zobrist::psq[us][KING][kfrom] ^ Zobrist::psq[us][KING][kto];
-      st->key ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
-
-      // Clear en passant square
-      if (st->epSquare != SQ_NONE)
-      {
-          st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
-          st->epSquare = SQ_NONE;
-      }
-
-      // Update castling rights
-      st->key ^= Zobrist::castle[st->castleRights & castleRightsMask[kfrom]];
-      st->castleRights &= ~castleRightsMask[kfrom];
-
-      // Update checkers BB
-      st->checkersBB = attackers_to(king_square(~us)) & pieces(us);
-
-      sideToMove = ~sideToMove;
-  }
-  else
-      // Undo: point our state pointer back to the previous state
-      st = st->previous;
-
-  assert(pos_is_ok());
 }
 
 
-/// Position::do_null_move() is used to do/undo a "null move": It flips the side
+/// Position::do(undo)_null_move() is used to do(undo) a "null move": It flips
-/// to move and updates the hash key without executing any move on the board.
+/// the side to move without executing any move on the board.
-template<bool Do>
+
-void Position::do_null_move(StateInfo& backupSt) {
+void Position::do_null_move(StateInfo& newSt) {
 
   assert(!checkers());
 
-  // Back up the information necessary to undo the null move to the supplied
+  memcpy(&newSt, st, sizeof(StateInfo)); // Fully copy here
-  // StateInfo object. Note that differently from normal case here backupSt
-  // is actually used as a backup storage not as the new state. This reduces
-  // the number of fields to be copied.
-  StateInfo* src = Do ? st : &backupSt;
-  StateInfo* dst = Do ? &backupSt : st;
 
-  dst->key      = src->key;
+  newSt.previous = st;
-  dst->epSquare = src->epSquare;
+  st = &newSt;
-  dst->psqScore = src->psqScore;
+
-  dst->rule50   = src->rule50;
+  if (st->epSquare != SQ_NONE)
-  dst->pliesFromNull = src->pliesFromNull;
+  {
+      st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
+      st->epSquare = SQ_NONE;
+  }
+
+  st->key ^= Zobrist::side;
+  prefetch((char*)TT.first_entry(st->key));
+
+  st->rule50++;
+  st->pliesFromNull = 0;
 
   sideToMove = ~sideToMove;
 
-  if (Do)
-  {
-      if (st->epSquare != SQ_NONE)
-          st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
-
-      st->key ^= Zobrist::side;
-      prefetch((char*)TT.first_entry(st->key));
-
-      st->epSquare = SQ_NONE;
-      st->rule50++;
-      st->pliesFromNull = 0;
-  }
-
   assert(pos_is_ok());
 }
 
-// Explicit template instantiations
+void Position::undo_null_move() {
-template void Position::do_null_move<false>(StateInfo& backupSt);
+
-template void Position::do_null_move<true>(StateInfo& backupSt);
+  assert(!checkers());
+
+  st = st->previous;
+  sideToMove = ~sideToMove;
+}
 
 
 /// Position::see() is a static exchange evaluator: It tries to estimate the
@@ -1422,31 +1363,36 @@ Value Position::compute_non_pawn_material(Color c) const {
 /// Position::is_draw() tests whether the position is drawn by material,
 /// repetition, or the 50 moves rule. It does not detect stalemates, this
 /// must be done by the search.
-template<bool CheckRepetition, bool CheckThreeFold>
+template<bool SkipRepetition>
 bool Position::is_draw() const {
 
+  // Draw by material?
   if (   !pieces(PAWN)
       && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
       return true;
 
+  // Draw by the 50 moves rule?
   if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
       return true;
 
-  if (CheckRepetition)
+  // Draw by repetition?
+  if (!SkipRepetition)
   {
-      int i = 4, e = std::min(st->rule50, st->pliesFromNull), cnt;
+      int i = 4, e = std::min(st->rule50, st->pliesFromNull);
 
       if (i <= e)
       {
           StateInfo* stp = st->previous->previous;
 
-          for (cnt = 0; i <= e; i += 2)
+          do {
-          {
               stp = stp->previous->previous;
 
-              if (stp->key == st->key && (!CheckThreeFold || ++cnt >= 2))
+              if (stp->key == st->key)
                   return true;
-          }
+
+              i += 2;
+
+          } while (i <= e);
       }
   }
 
@@ -1454,9 +1400,8 @@ bool Position::is_draw() const {
 }
 
 // Explicit template instantiations
-template bool Position::is_draw<true,  true>() const;
+template bool Position::is_draw<false>() const;
-template bool Position::is_draw<true, false>() const;
+template bool Position::is_draw<true>() const;
-template bool Position::is_draw<false,false>() const;
 
 
 /// Position::flip() flips position with the white and black sides reversed. This

src/position.h

@@ -154,7 +154,8 @@ public:
   void do_move(Move m, StateInfo& st);
   void do_move(Move m, StateInfo& st, const CheckInfo& ci, bool moveIsCheck);
   void undo_move(Move m);
-  template<bool Do> void do_null_move(StateInfo& st);
+  void do_null_move(StateInfo& st);
+  void undo_null_move();
 
   // Static exchange evaluation
   int see(Move m) const;
@@ -178,7 +179,7 @@ public:
   Thread* this_thread() const;
   int64_t nodes_searched() const;
   void set_nodes_searched(int64_t n);
-  template<bool CheckRepetition, bool CheckThreeFold> bool is_draw() const;
+  template<bool SkipRepetition> bool is_draw() const;
 
   // Position consistency check, for debugging
   bool pos_is_ok(int* failedStep = NULL) const;
@@ -190,8 +191,8 @@ private:
   void put_piece(Piece p, Square s);
   void set_castle_right(Color c, Square rfrom);
 
-  // Helper template functions
+  // Helper functions
-  template<bool Do> void do_castle_move(Move m);
+  void do_castle(Square kfrom, Square kto, Square rfrom, Square rto);
   template<bool FindPinned> Bitboard hidden_checkers() const;
 
   // Computing hash keys from scratch (for initialization and debugging)

src/search.cpp

@@ -26,7 +26,6 @@
 
 #include "book.h"
 #include "evaluate.h"
-#include "history.h"
 #include "movegen.h"
 #include "movepick.h"
 #include "notation.h"
@@ -87,7 +86,8 @@ namespace {
   TimeManager TimeMgr;
   int BestMoveChanges;
   Value DrawValue[COLOR_NB];
-  History H;
+  History Hist;
+  Gains Gain;
 
   template <NodeType NT>
   Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
@@ -98,8 +98,9 @@ namespace {
   void id_loop(Position& pos);
   Value value_to_tt(Value v, int ply);
   Value value_from_tt(Value v, int ply);
-  bool check_is_dangerous(Position& pos, Move move, Value futilityBase, Value beta);
+  bool check_is_dangerous(const Position& pos, Move move, Value futilityBase, Value beta);
-  bool prevents_move(const Position& pos, Move first, Move second);
+  bool allows(const Position& pos, Move first, Move second);
+  bool refutes(const Position& pos, Move first, Move second);
   string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
 
   struct Skill {
@@ -228,22 +229,22 @@ void Search::think() {
 
   // Reset the threads, still sleeping: will be wake up at split time
   for (size_t i = 0; i < Threads.size(); i++)
-      Threads[i].maxPly = 0;
+      Threads[i]->maxPly = 0;
 
   Threads.sleepWhileIdle = Options["Use Sleeping Threads"];
 
   // Set best timer interval to avoid lagging under time pressure. Timer is
   // used to check for remaining available thinking time.
-  Threads.timer_thread()->msec =
+  Threads.timer->msec =
   Limits.use_time_management() ? std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)) :
                   Limits.nodes ? 2 * TimerResolution
                                : 100;
 
-  Threads.timer_thread()->notify_one(); // Wake up the recurring timer
+  Threads.timer->notify_one(); // Wake up the recurring timer
 
   id_loop(RootPos); // Let's start searching !
 
-  Threads.timer_thread()->msec = 0; // Stop the timer
+  Threads.timer->msec = 0; // Stop the timer
   Threads.sleepWhileIdle = true; // Send idle threads to sleep
 
   if (Options["Use Search Log"])
@@ -299,7 +300,8 @@ namespace {
     bestValue = delta = -VALUE_INFINITE;
     ss->currentMove = MOVE_NULL; // Hack to skip update gains
     TT.new_search();
-    H.clear();
+    Hist.clear();
+    Gain.clear();
 
     PVSize = Options["MultiPV"];
     Skill skill(Options["Skill Level"]);
@@ -352,7 +354,7 @@ namespace {
                 // we want to keep the same order for all the moves but the new
                 // PV that goes to the front. Note that in case of MultiPV search
                 // the already searched PV lines are preserved.
-                sort<RootMove>(RootMoves.begin() + PVIdx, RootMoves.end());
+                std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
 
                 // Write PV back to transposition table in case the relevant
                 // entries have been overwritten during the search.
@@ -397,7 +399,8 @@ namespace {
             }
 
             // Sort the PV lines searched so far and update the GUI
-            sort<RootMove>(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
+            std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
+
             if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
                 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
         }
@@ -534,7 +537,7 @@ namespace {
     if (!RootNode)
     {
         // Step 2. Check for aborted search and immediate draw
-        if (Signals.stop || pos.is_draw<true, PvNode>() || ss->ply > MAX_PLY)
+        if (Signals.stop || pos.is_draw<false>() || ss->ply > MAX_PLY)
             return DrawValue[pos.side_to_move()];
 
         // Step 3. Mate distance pruning. Even if we mate at the next move our score
@@ -591,8 +594,8 @@ namespace {
     else if (tte)
     {
         // Never assume anything on values stored in TT
-        if (  (ss->staticEval = eval = tte->static_value()) == VALUE_NONE
+        if (  (ss->staticEval = eval = tte->eval_value()) == VALUE_NONE
-            ||(ss->evalMargin = tte->static_value_margin()) == VALUE_NONE)
+            ||(ss->evalMargin = tte->eval_margin()) == VALUE_NONE)
             eval = ss->staticEval = evaluate(pos, ss->evalMargin);
 
         // Can ttValue be used as a better position evaluation?
@@ -617,7 +620,7 @@ namespace {
         &&  type_of(move) == NORMAL)
     {
         Square to = to_sq(move);
-        H.update_gain(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
+        Gain.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
     }
 
     // Step 6. Razoring (is omitted in PV nodes)
@@ -667,12 +670,12 @@ namespace {
         if (eval - PawnValueMg > beta)
             R += ONE_PLY;
 
-        pos.do_null_move<true>(st);
+        pos.do_null_move(st);
         (ss+1)->skipNullMove = true;
         nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
                                       : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R);
         (ss+1)->skipNullMove = false;
-        pos.do_null_move<false>(st);
+        pos.undo_null_move();
 
         if (nullValue >= beta)
         {
@@ -692,9 +695,21 @@ namespace {
                 return nullValue;
         }
         else
+        {
             // The null move failed low, which means that we may be faced with
-            // some kind of threat.
+            // some kind of threat. If the previous move was reduced, check if
+            // the move that refuted the null move was somehow connected to the
+            // move which was reduced. If a connection is found, return a fail
+            // low score (which will cause the reduced move to fail high in the
+            // parent node, which will trigger a re-search with full depth).
             threatMove = (ss+1)->currentMove;
+
+            if (   depth < 5 * ONE_PLY
+                && (ss-1)->reduction
+                && threatMove != MOVE_NONE
+                && allows(pos, (ss-1)->currentMove, threatMove))
+                return beta - 1;
+        }
     }
 
     // Step 9. ProbCut (is omitted in PV nodes)
@@ -715,7 +730,7 @@ namespace {
         assert((ss-1)->currentMove != MOVE_NONE);
         assert((ss-1)->currentMove != MOVE_NULL);
 
-        MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
+        MovePicker mp(pos, ttMove, Hist, pos.captured_piece_type());
         CheckInfo ci(pos);
 
         while ((move = mp.next_move<false>()) != MOVE_NONE)
@@ -747,7 +762,7 @@ namespace {
 
 split_point_start: // At split points actual search starts from here
 
-    MovePicker mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
+    MovePicker mp(pos, ttMove, depth, Hist, ss, PvNode ? -VALUE_INFINITE : beta);
     CheckInfo ci(pos);
     value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
     singularExtensionNode =   !RootNode
@@ -847,12 +862,13 @@ split_point_start: // At split points actual search starts from here
           && !inCheck
           && !dangerous
           &&  move != ttMove
-          && (!threatMove || !prevents_move(pos, move, threatMove))
           && (bestValue > VALUE_MATED_IN_MAX_PLY || (   bestValue == -VALUE_INFINITE
                                                      && alpha > VALUE_MATED_IN_MAX_PLY)))
       {
           // Move count based pruning
-          if (depth < 16 * ONE_PLY && moveCount >= FutilityMoveCounts[depth])
+          if (   depth < 16 * ONE_PLY
+              && moveCount >= FutilityMoveCounts[depth]
+              && (!threatMove || !refutes(pos, move, threatMove)))
           {
               if (SpNode)
                   sp->mutex.lock();
@@ -865,7 +881,7 @@ split_point_start: // At split points actual search starts from here
           // but fixing this made program slightly weaker.
           Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
           futilityValue =  ss->staticEval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
-                         + H.gain(pos.piece_moved(move), to_sq(move));
+                         + Gain[pos.piece_moved(move)][to_sq(move)];
 
           if (futilityValue < beta)
           {
@@ -907,8 +923,9 @@ split_point_start: // At split points actual search starts from here
           && !pvMove
           && !captureOrPromotion
           && !dangerous
-          &&  ss->killers[0] != move
+          &&  move != ttMove
-          &&  ss->killers[1] != move)
+          &&  move != ss->killers[0]
+          &&  move != ss->killers[1])
       {
           ss->reduction = reduction<PvNode>(depth, moveCount);
           Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
@@ -1008,13 +1025,13 @@ split_point_start: // At split points actual search starts from here
       // Step 19. Check for splitting the search
       if (   !SpNode
           &&  depth >= Threads.minimumSplitDepth
-          &&  Threads.slave_available(thisThread)
+          &&  Threads.available_slave(thisThread)
           &&  thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
       {
           assert(bestValue < beta);
 
-          bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
+          thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
-                                               depth, threatMove, moveCount, mp, NT);
+                                       depth, threatMove, moveCount, &mp, NT);
           if (bestValue >= beta)
               break;
       }
@@ -1057,13 +1074,13 @@ split_point_start: // At split points actual search starts from here
 
             // Increase history value of the cut-off move
             Value bonus = Value(int(depth) * int(depth));
-            H.add(pos.piece_moved(bestMove), to_sq(bestMove), bonus);
+            Hist.update(pos.piece_moved(bestMove), to_sq(bestMove), bonus);
 
             // Decrease history of all the other played non-capture moves
             for (int i = 0; i < playedMoveCount - 1; i++)
             {
                 Move m = movesSearched[i];
-                H.add(pos.piece_moved(m), to_sq(m), -bonus);
+                Hist.update(pos.piece_moved(m), to_sq(m), -bonus);
             }
         }
     }
@@ -1109,7 +1126,7 @@ split_point_start: // At split points actual search starts from here
     ss->ply = (ss-1)->ply + 1;
 
     // Check for an instant draw or maximum ply reached
-    if (pos.is_draw<false, false>() || ss->ply > MAX_PLY)
+    if (pos.is_draw<true>() || ss->ply > MAX_PLY)
         return DrawValue[pos.side_to_move()];
 
     // Transposition table lookup. At PV nodes, we don't use the TT for
@@ -1147,8 +1164,8 @@ split_point_start: // At split points actual search starts from here
         if (tte)
         {
             // Never assume anything on values stored in TT
-            if (  (ss->staticEval = bestValue = tte->static_value()) == VALUE_NONE
+            if (  (ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE
-                ||(ss->evalMargin = tte->static_value_margin()) == VALUE_NONE)
+                ||(ss->evalMargin = tte->eval_margin()) == VALUE_NONE)
                 ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
         }
         else
@@ -1175,7 +1192,7 @@ split_point_start: // At split points actual search starts from here
     // to search the moves. Because the depth is <= 0 here, only captures,
     // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
     // be generated.
-    MovePicker mp(pos, ttMove, depth, H, to_sq((ss-1)->currentMove));
+    MovePicker mp(pos, ttMove, depth, Hist, to_sq((ss-1)->currentMove));
     CheckInfo ci(pos);
 
     // Loop through the moves until no moves remain or a beta cutoff occurs
@@ -1318,7 +1335,7 @@ split_point_start: // At split points actual search starts from here
 
   // check_is_dangerous() tests if a checking move can be pruned in qsearch()
 
-  bool check_is_dangerous(Position& pos, Move move, Value futilityBase, Value beta)
+  bool check_is_dangerous(const Position& pos, Move move, Value futilityBase, Value beta)
   {
     Piece pc = pos.piece_moved(move);
     Square from = from_sq(move);
@@ -1343,6 +1360,7 @@ split_point_start: // At split points actual search starts from here
     Bitboard b = (enemies ^ ksq) & newAtt & ~oldAtt;
     while (b)
     {
+        // Note that here we generate illegal "double move"!
         if (futilityBase + PieceValue[EG][pos.piece_on(pop_lsb(&b))] >= beta)
             return true;
     }
@@ -1351,12 +1369,52 @@ split_point_start: // At split points actual search starts from here
   }
 
 
-  // prevents_move() tests whether a move (first) is able to defend against an
+  // allows() tests whether the 'first' move at previous ply somehow makes the
-  // opponent's move (second). In this case will not be pruned. Normally the
+  // 'second' move possible, for instance if the moving piece is the same in
-  // second move is the threat move (the best move returned from a null search
+  // both moves. Normally the second move is the threat (the best move returned
-  // that fails low).
+  // from a null search that fails low).
 
-  bool prevents_move(const Position& pos, Move first, Move second) {
+  bool allows(const Position& pos, Move first, Move second) {
+
+    assert(is_ok(first));
+    assert(is_ok(second));
+    assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
+    assert(color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
+
+    Square m1from = from_sq(first);
+    Square m2from = from_sq(second);
+    Square m1to = to_sq(first);
+    Square m2to = to_sq(second);
+
+    // The piece is the same or second's destination was vacated by the first move
+    if (m1to == m2from || m2to == m1from)
+        return true;
+
+    // Second one moves through the square vacated by first one
+    if (between_bb(m2from, m2to) & m1from)
+      return true;
+
+    // Second's destination is defended by the first move's piece
+    Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
+    if (m1att & m2to)
+        return true;
+
+    // Second move gives a discovered check through the first's checking piece
+    if (m1att & pos.king_square(pos.side_to_move()))
+    {
+        assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);
+        return true;
+    }
+
+    return false;
+  }
+
+
+  // refutes() tests whether a 'first' move is able to defend against a 'second'
+  // opponent's move. In this case will not be pruned. Normally the second move
+  // is the threat (the best move returned from a null search that fails low).
+
+  bool refutes(const Position& pos, Move first, Move second) {
 
     assert(is_ok(first));
     assert(is_ok(second));
@@ -1455,8 +1513,8 @@ split_point_start: // At split points actual search starts from here
     int selDepth = 0;
 
     for (size_t i = 0; i < Threads.size(); i++)
-        if (Threads[i].maxPly > selDepth)
+        if (Threads[i]->maxPly > selDepth)
-            selDepth = Threads[i].maxPly;
+            selDepth = Threads[i]->maxPly;
 
     for (size_t i = 0; i < uciPVSize; i++)
     {
@@ -1516,7 +1574,7 @@ void RootMove::extract_pv_from_tt(Position& pos) {
            && pos.is_pseudo_legal(m = tte->move()) // Local copy, TT could change
            && pos.pl_move_is_legal(m, pos.pinned_pieces())
            && ply < MAX_PLY
-           && (!pos.is_draw<true, true>() || ply < 2));
+           && (!pos.is_draw<false>() || ply < 2));
 
   pv.push_back(MOVE_NONE); // Must be zero-terminating
 
@@ -1558,7 +1616,7 @@ void Thread::idle_loop() {
   // at the thread creation. So it means we are the split point's master.
   const SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
 
-  assert(!this_sp || (this_sp->master == this && searching));
+  assert(!this_sp || (this_sp->masterThread == this && searching));
 
   // If this thread is the master of a split point and all slaves have finished
   // their work at this split point, return from the idle loop.
@@ -1614,9 +1672,9 @@ void Thread::idle_loop() {
 
           sp->mutex.lock();
 
-          assert(sp->slavesPositions[idx] == NULL);
+          assert(activePosition == NULL);
 
-          sp->slavesPositions[idx] = &pos;
+          activePosition = &pos;
 
           switch (sp->nodeType) {
           case Root:
@@ -1635,18 +1693,18 @@ void Thread::idle_loop() {
           assert(searching);
 
           searching = false;
-          sp->slavesPositions[idx] = NULL;
+          activePosition = NULL;
           sp->slavesMask &= ~(1ULL << idx);
           sp->nodes += pos.nodes_searched();
 
           // Wake up master thread so to allow it to return from the idle loop
           // in case we are the last slave of the split point.
           if (    Threads.sleepWhileIdle
-              &&  this != sp->master
+              &&  this != sp->masterThread
               && !sp->slavesMask)
           {
-              assert(!sp->master->searching);
+              assert(!sp->masterThread->searching);
-              sp->master->notify_one();
+              sp->masterThread->notify_one();
           }
 
           // After releasing the lock we cannot access anymore any SplitPoint
@@ -1684,11 +1742,11 @@ void check_time() {
       nodes = RootPos.nodes_searched();
 
       // Loop across all split points and sum accumulated SplitPoint nodes plus
-      // all the currently active slaves positions.
+      // all the currently active positions nodes.
       for (size_t i = 0; i < Threads.size(); i++)
-          for (int j = 0; j < Threads[i].splitPointsSize; j++)
+          for (int j = 0; j < Threads[i]->splitPointsSize; j++)
           {
-              SplitPoint& sp = Threads[i].splitPoints[j];
+              SplitPoint& sp = Threads[i]->splitPoints[j];
 
               sp.mutex.lock();
 
@@ -1696,8 +1754,9 @@ void check_time() {
               Bitboard sm = sp.slavesMask;
               while (sm)
               {
-                  Position* pos = sp.slavesPositions[pop_lsb(&sm)];
+                  Position* pos = Threads[pop_lsb(&sm)]->activePosition;
-                  nodes += pos ? pos->nodes_searched() : 0;
+                  if (pos)
+                      nodes += pos->nodes_searched();
               }
 
               sp.mutex.unlock();

src/search.h

@@ -56,12 +56,11 @@ struct Stack {
 /// all non-pv moves.
 struct RootMove {
 
-  RootMove(){} // Needed by sort()
   RootMove(Move m) : score(-VALUE_INFINITE), prevScore(-VALUE_INFINITE) {
     pv.push_back(m); pv.push_back(MOVE_NONE);
   }
 
-  bool operator<(const RootMove& m) const { return score < m.score; }
+  bool operator<(const RootMove& m) const { return score > m.score; } // Ascending sort
   bool operator==(const Move& m) const { return pv[0] == m; }
 
   void extract_pv_from_tt(Position& pos);

src/thread.cpp

@@ -17,6 +17,7 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <algorithm> // For std::count
 #include <cassert>
 #include <iostream>
 
@@ -42,11 +43,12 @@ namespace { extern "C" {
 // Thread c'tor starts a newly-created thread of execution that will call
 // the the virtual function idle_loop(), going immediately to sleep.
 
-Thread::Thread() : splitPoints() {
+Thread::Thread() /* : splitPoints() */ { // Value-initialization bug in MSVC
 
   searching = exit = false;
   maxPly = splitPointsSize = 0;
   activeSplitPoint = NULL;
+  activePosition = NULL;
   idx = Threads.size();
 
   if (!thread_create(handle, start_routine, this))
@@ -146,7 +148,7 @@ void Thread::wait_for(volatile const bool& b) {
 
 bool Thread::cutoff_occurred() const {
 
-  for (SplitPoint* sp = activeSplitPoint; sp; sp = sp->parent)
+  for (SplitPoint* sp = activeSplitPoint; sp; sp = sp->parentSplitPoint)
       if (sp->cutoff)
           return true;
 
@@ -185,7 +187,7 @@ void ThreadPool::init() {
 
   sleepWhileIdle = true;
   timer = new TimerThread();
-  threads.push_back(new MainThread());
+  push_back(new MainThread());
   read_uci_options();
 }
 
@@ -196,8 +198,8 @@ void ThreadPool::exit() {
 
   delete timer; // As first because check_time() accesses threads data
 
-  for (size_t i = 0; i < threads.size(); i++)
+  for (iterator it = begin(); it != end(); ++it)
-      delete threads[i];
+      delete *it;
 }
 
 
@@ -214,13 +216,13 @@ void ThreadPool::read_uci_options() {
 
   assert(requested > 0);
 
-  while (threads.size() < requested)
+  while (size() < requested)
-      threads.push_back(new Thread());
+      push_back(new Thread());
 
-  while (threads.size() > requested)
+  while (size() > requested)
   {
-      delete threads.back();
+      delete back();
-      threads.pop_back();
+      pop_back();
   }
 }
 
@@ -228,13 +230,13 @@ void ThreadPool::read_uci_options() {
 // slave_available() tries to find an idle thread which is available as a slave
 // for the thread 'master'.
 
-bool ThreadPool::slave_available(Thread* master) const {
+Thread* ThreadPool::available_slave(Thread* master) const {
 
-  for (size_t i = 0; i < threads.size(); i++)
+  for (const_iterator it = begin(); it != end(); ++it)
-      if (threads[i]->is_available_to(master))
+      if ((*it)->is_available_to(master))
-          return true;
+          return *it;
 
-  return false;
+  return NULL;
 }
 
 
@@ -248,34 +250,31 @@ bool ThreadPool::slave_available(Thread* master) const {
 // search() then split() returns.
 
 template <bool Fake>
-Value ThreadPool::split(Position& pos, Stack* ss, Value alpha, Value beta,
+void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bestValue,
-                        Value bestValue, Move* bestMove, Depth depth, Move threatMove,
+                   Move* bestMove, Depth depth, Move threatMove, int moveCount,
-                        int moveCount, MovePicker& mp, int nodeType) {
+                   MovePicker* movePicker, int nodeType) {
 
   assert(pos.pos_is_ok());
-  assert(bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
+  assert(*bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
-  assert(bestValue > -VALUE_INFINITE);
+  assert(*bestValue > -VALUE_INFINITE);
   assert(depth >= Threads.minimumSplitDepth);
-
+  assert(searching);
-  Thread* master = pos.this_thread();
+  assert(splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);
-
-  assert(master->searching);
-  assert(master->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);
 
   // Pick the next available split point from the split point stack
-  SplitPoint& sp = master->splitPoints[master->splitPointsSize];
+  SplitPoint& sp = splitPoints[splitPointsSize];
 
-  sp.master = master;
+  sp.masterThread = this;
-  sp.parent = master->activeSplitPoint;
+  sp.parentSplitPoint = activeSplitPoint;
-  sp.slavesMask = 1ULL << master->idx;
+  sp.slavesMask = 1ULL << idx;
   sp.depth = depth;
+  sp.bestValue = *bestValue;
   sp.bestMove = *bestMove;
   sp.threatMove = threatMove;
   sp.alpha = alpha;
   sp.beta = beta;
   sp.nodeType = nodeType;
-  sp.bestValue = bestValue;
+  sp.movePicker = movePicker;
-  sp.mp = &mp;
   sp.moveCount = moveCount;
   sp.pos = &pos;
   sp.nodes = 0;
@@ -285,25 +284,27 @@ Value ThreadPool::split(Position& pos, Stack* ss, Value alpha, Value beta,
   // Try to allocate available threads and ask them to start searching setting
   // 'searching' flag. This must be done under lock protection to avoid concurrent
   // allocation of the same slave by another master.
-  mutex.lock();
+  Threads.mutex.lock();
   sp.mutex.lock();
 
-  master->splitPointsSize++;
+  splitPointsSize++;
-  master->activeSplitPoint = &sp;
+  activeSplitPoint = &sp;
+  activePosition = NULL;
 
-  size_t slavesCnt = 1; // Master is always included
+  size_t slavesCnt = 1; // This thread is always included
+  Thread* slave;
 
-  for (size_t i = 0; i < threads.size() && !Fake; ++i)
+  while (    (slave = Threads.available_slave(this)) != NULL
-      if (threads[i]->is_available_to(master) && ++slavesCnt <= maxThreadsPerSplitPoint)
+         && ++slavesCnt <= Threads.maxThreadsPerSplitPoint && !Fake)
-      {
+  {
-          sp.slavesMask |= 1ULL << threads[i]->idx;
+      sp.slavesMask |= 1ULL << slave->idx;
-          threads[i]->activeSplitPoint = &sp;
+      slave->activeSplitPoint = &sp;
-          threads[i]->searching = true; // Slave leaves idle_loop()
+      slave->searching = true; // Slave leaves idle_loop()
-          threads[i]->notify_one(); // Could be sleeping
+      slave->notify_one(); // Could be sleeping
-      }
+  }
 
   sp.mutex.unlock();
-  mutex.unlock();
+  Threads.mutex.unlock();
 
   // Everything is set up. The master thread enters the idle loop, from which
   // it will instantly launch a search, because its 'searching' flag is set.
@@ -311,34 +312,35 @@ Value ThreadPool::split(Position& pos, Stack* ss, Value alpha, Value beta,
   // their work at this split point.
   if (slavesCnt > 1 || Fake)
   {
-      master->Thread::idle_loop(); // Force a call to base class idle_loop()
+      Thread::idle_loop(); // Force a call to base class idle_loop()
 
       // In helpful master concept a master can help only a sub-tree of its split
       // point, and because here is all finished is not possible master is booked.
-      assert(!master->searching);
+      assert(!searching);
+      assert(!activePosition);
   }
 
   // We have returned from the idle loop, which means that all threads are
   // finished. Note that setting 'searching' and decreasing splitPointsSize is
   // done under lock protection to avoid a race with Thread::is_available_to().
-  mutex.lock();
+  Threads.mutex.lock();
   sp.mutex.lock();
 
-  master->searching = true;
+  searching = true;
-  master->splitPointsSize--;
+  splitPointsSize--;
-  master->activeSplitPoint = sp.parent;
+  activeSplitPoint = sp.parentSplitPoint;
+  activePosition = &pos;
   pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
   *bestMove = sp.bestMove;
+  *bestValue = sp.bestValue;
 
   sp.mutex.unlock();
-  mutex.unlock();
+  Threads.mutex.unlock();
-
-  return sp.bestValue;
 }
 
 // Explicit template instantiations
-template Value ThreadPool::split<false>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
+template void Thread::split<false>(Position&, Stack*, Value, Value, Value*, Move*, Depth, Move, int, MovePicker*, int);
-template Value ThreadPool::split<true>(Position&, Stack*, Value, Value, Value, Move*, Depth, Move, int, MovePicker&, int);
+template void Thread::split< true>(Position&, Stack*, Value, Value, Value*, Move*, Depth, Move, int, MovePicker*, int);
 
 
 // wait_for_think_finished() waits for main thread to go to sleep then returns
@@ -370,7 +372,8 @@ void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
   RootMoves.clear();
 
   for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
-      if (searchMoves.empty() || count(searchMoves.begin(), searchMoves.end(), ml.move()))
+      if (   searchMoves.empty()
+          || std::count(searchMoves.begin(), searchMoves.end(), ml.move()))
           RootMoves.push_back(RootMove(ml.move()));
 
   main_thread()->thinking = true;

src/thread.h

@@ -63,19 +63,18 @@ struct SplitPoint {
   // Const data after split point has been setup
   const Position* pos;
   const Search::Stack* ss;
-  Thread* master;
+  Thread* masterThread;
   Depth depth;
   Value beta;
   int nodeType;
   Move threatMove;
 
   // Const pointers to shared data
-  MovePicker* mp;
+  MovePicker* movePicker;
-  SplitPoint* parent;
+  SplitPoint* parentSplitPoint;
 
   // Shared data
   Mutex mutex;
-  Position* slavesPositions[MAX_THREADS];
   volatile uint64_t slavesMask;
   volatile int64_t nodes;
   volatile Value alpha;
@@ -102,10 +101,15 @@ struct Thread {
   bool is_available_to(Thread* master) const;
   void wait_for(volatile const bool& b);
 
+  template <bool Fake>
+  void split(Position& pos, Search::Stack* ss, Value alpha, Value beta, Value* bestValue, Move* bestMove,
+             Depth depth, Move threatMove, int moveCount, MovePicker* movePicker, int nodeType);
+
   SplitPoint splitPoints[MAX_SPLITPOINTS_PER_THREAD];
   Material::Table materialTable;
   Endgames endgames;
   Pawns::Table pawnsTable;
+  Position* activePosition;
   size_t idx;
   int maxPly;
   Mutex mutex;
@@ -134,40 +138,28 @@ struct TimerThread : public Thread {
 };
 
 
-/// ThreadPool class handles all the threads related stuff like init, starting,
+/// ThreadPool struct handles all the threads related stuff like init, starting,
 /// parking and, the most important, launching a slave thread at a split point.
 /// All the access to shared thread data is done through this class.
 
-class ThreadPool {
+struct ThreadPool : public std::vector<Thread*> {
 
-public:
   void init(); // No c'tor and d'tor, threads rely on globals that should
   void exit(); // be initialized and valid during the whole thread lifetime.
 
-  Thread& operator[](size_t id) { return *threads[id]; }
+  MainThread* main_thread() { return static_cast<MainThread*>((*this)[0]); }
-  size_t size() const { return threads.size(); }
-  MainThread* main_thread() { return static_cast<MainThread*>(threads[0]); }
-  TimerThread* timer_thread() { return timer; }
-
   void read_uci_options();
-  bool slave_available(Thread* master) const;
+  Thread* available_slave(Thread* master) const;
   void wait_for_think_finished();
   void start_thinking(const Position&, const Search::LimitsType&,
                       const std::vector<Move>&, Search::StateStackPtr&);
 
-  template <bool Fake>
-  Value split(Position& pos, Search::Stack* ss, Value alpha, Value beta, Value bestValue, Move* bestMove,
-              Depth depth, Move threatMove, int moveCount, MovePicker& mp, int nodeType);
-
   bool sleepWhileIdle;
   Depth minimumSplitDepth;
+  size_t maxThreadsPerSplitPoint;
   Mutex mutex;
   ConditionVariable sleepCondition;
-
-private:
-  std::vector<Thread*> threads;
   TimerThread* timer;
-  size_t maxThreadsPerSplitPoint;
 };
 
 extern ThreadPool Threads;

src/tt.cpp

@@ -25,35 +25,25 @@
 
 TranspositionTable TT; // Our global transposition table
 
-TranspositionTable::TranspositionTable() {
-
-  size = generation = 0;
-  entries = NULL;
-}
-
-TranspositionTable::~TranspositionTable() {
-
-  delete [] entries;
-}
-
 
 /// TranspositionTable::set_size() sets the size of the transposition table,
-/// measured in megabytes. Transposition table consists of a power of 2 number of
+/// measured in megabytes. Transposition table consists of a power of 2 number
-/// TTCluster and each cluster consists of ClusterSize number of TTEntries. Each
+/// of clusters and each cluster consists of ClusterSize number of TTEntry.
-/// non-empty entry contains information of exactly one position.
 
 void TranspositionTable::set_size(size_t mbSize) {
 
-  size_t newSize = 1ULL << msb((mbSize << 20) / sizeof(TTCluster));
+  assert(msb((mbSize << 20) / sizeof(TTEntry)) < 32);
 
-  if (newSize == size)
+  uint32_t size = ClusterSize << msb((mbSize << 20) / sizeof(TTEntry[ClusterSize]));
+
+  if (hashMask == size - ClusterSize)
       return;
 
-  size = newSize;
+  hashMask = size - ClusterSize;
-  delete [] entries;
+  delete [] table;
-  entries = new (std::nothrow) TTCluster[size];
+  table = new (std::nothrow) TTEntry[size];
 
-  if (!entries)
+  if (!table)
   {
       std::cerr << "Failed to allocate " << mbSize
                 << "MB for transposition table." << std::endl;
@@ -70,7 +60,7 @@ void TranspositionTable::set_size(size_t mbSize) {
 
 void TranspositionTable::clear() {
 
-  memset(entries, 0, size * sizeof(TTCluster));
+  memset(table, 0, (hashMask + ClusterSize) * sizeof(TTEntry));
 }
 
 
@@ -82,23 +72,23 @@ void TranspositionTable::clear() {
 /// more valuable than a TTEntry t2 if t1 is from the current search and t2 is from
 /// a previous search, or if the depth of t1 is bigger than the depth of t2.
 
-void TranspositionTable::store(const Key posKey, Value v, Bound t, Depth d, Move m, Value statV, Value kingD) {
+void TranspositionTable::store(const Key key, Value v, Bound t, Depth d, Move m, Value statV, Value kingD) {
 
   int c1, c2, c3;
   TTEntry *tte, *replace;
-  uint32_t posKey32 = posKey >> 32; // Use the high 32 bits as key inside the cluster
+  uint32_t key32 = key >> 32; // Use the high 32 bits as key inside the cluster
 
-  tte = replace = first_entry(posKey);
+  tte = replace = first_entry(key);
 
-  for (int i = 0; i < ClusterSize; i++, tte++)
+  for (unsigned i = 0; i < ClusterSize; i++, tte++)
   {
-      if (!tte->key() || tte->key() == posKey32) // Empty or overwrite old
+      if (!tte->key() || tte->key() == key32) // Empty or overwrite old
       {
           // Preserve any existing ttMove
           if (m == MOVE_NONE)
               m = tte->move();
 
-          tte->save(posKey32, v, t, d, m, generation, statV, kingD);
+          tte->save(key32, v, t, d, m, generation, statV, kingD);
           return;
       }
 
@@ -110,7 +100,7 @@ void TranspositionTable::store(const Key posKey, Value v, Bound t, Depth d, Move
       if (c1 + c2 + c3 > 0)
           replace = tte;
   }
-  replace->save(posKey32, v, t, d, m, generation, statV, kingD);
+  replace->save(key32, v, t, d, m, generation, statV, kingD);
 }
 
 
@@ -118,24 +108,14 @@ void TranspositionTable::store(const Key posKey, Value v, Bound t, Depth d, Move
 /// transposition table. Returns a pointer to the TTEntry or NULL if
 /// position is not found.
 
-TTEntry* TranspositionTable::probe(const Key posKey) const {
+TTEntry* TranspositionTable::probe(const Key key) const {
 
-  uint32_t posKey32 = posKey >> 32;
+  TTEntry* tte = first_entry(key);
-  TTEntry* tte = first_entry(posKey);
+  uint32_t key32 = key >> 32;
 
-  for (int i = 0; i < ClusterSize; i++, tte++)
+  for (unsigned i = 0; i < ClusterSize; i++, tte++)
-      if (tte->key() == posKey32)
+      if (tte->key() == key32)
           return tte;
 
   return NULL;
 }
-
-
-/// TranspositionTable::new_search() is called at the beginning of every new
-/// search. It increments the "generation" variable, which is used to
-/// distinguish transposition table entries from previous searches from
-/// entries from the current search.
-
-void TranspositionTable::new_search() {
-  generation++;
-}

src/tt.h

@@ -44,7 +44,7 @@
 class TTEntry {
 
 public:
-  void save(uint32_t k, Value v, Bound b, Depth d, Move m, int g, Value statV, Value statM) {
+  void save(uint32_t k, Value v, Bound b, Depth d, Move m, int g, Value ev, Value em) {
 
     key32        = (uint32_t)k;
     move16       = (uint16_t)m;
@@ -52,63 +52,52 @@ public:
     generation8  = (uint8_t)g;
     value16      = (int16_t)v;
     depth16      = (int16_t)d;
-    staticValue  = (int16_t)statV;
+    evalValue    = (int16_t)ev;
-    staticMargin = (int16_t)statM;
+    evalMargin   = (int16_t)em;
   }
   void set_generation(int g) { generation8 = (uint8_t)g; }
 
-  uint32_t key() const              { return key32; }
+  uint32_t key() const      { return key32; }
-  Depth depth() const               { return (Depth)depth16; }
+  Depth depth() const       { return (Depth)depth16; }
-  Move move() const                 { return (Move)move16; }
+  Move move() const         { return (Move)move16; }
-  Value value() const               { return (Value)value16; }
+  Value value() const       { return (Value)value16; }
-  Bound type() const                { return (Bound)bound; }
+  Bound type() const        { return (Bound)bound; }
-  int generation() const            { return (int)generation8; }
+  int generation() const    { return (int)generation8; }
-  Value static_value() const        { return (Value)staticValue; }
+  Value eval_value() const  { return (Value)evalValue; }
-  Value static_value_margin() const { return (Value)staticMargin; }
+  Value eval_margin() const { return (Value)evalMargin; }
 
 private:
   uint32_t key32;
   uint16_t move16;
   uint8_t bound, generation8;
-  int16_t value16, depth16, staticValue, staticMargin;
+  int16_t value16, depth16, evalValue, evalMargin;
 };
 
 
-/// This is the number of TTEntry slots for each cluster
+/// A TranspositionTable consists of a power of 2 number of clusters and each
-const int ClusterSize = 4;
+/// cluster consists of ClusterSize number of TTEntry. Each non-empty entry
-
+/// contains information of exactly one position. Size of a cluster shall not be
-
+/// bigger than a cache line size. In case it is less, it should be padded to
-/// TTCluster consists of ClusterSize number of TTEntries. Size of TTCluster
+/// guarantee always aligned accesses.
-/// must not be bigger than a cache line size. In case it is less, it should
-/// be padded to guarantee always aligned accesses.
-
-struct TTCluster {
-  TTEntry data[ClusterSize];
-};
-
-
-/// The transposition table class. This is basically just a huge array containing
-/// TTCluster objects, and a few methods for writing and reading entries.
 
 class TranspositionTable {
 
-  TranspositionTable(const TranspositionTable&);
+  static const unsigned ClusterSize = 4; // A cluster is 64 Bytes
-  TranspositionTable& operator=(const TranspositionTable&);
 
 public:
-  TranspositionTable();
+ ~TranspositionTable() { delete [] table; }
- ~TranspositionTable();
+  void new_search() { generation++; }
+
+  TTEntry* probe(const Key key) const;
+  TTEntry* first_entry(const Key key) const;
+  void refresh(const TTEntry* tte) const;
   void set_size(size_t mbSize);
   void clear();
-  void store(const Key posKey, Value v, Bound type, Depth d, Move m, Value statV, Value kingD);
+  void store(const Key key, Value v, Bound type, Depth d, Move m, Value statV, Value kingD);
-  TTEntry* probe(const Key posKey) const;
-  void new_search();
-  TTEntry* first_entry(const Key posKey) const;
-  void refresh(const TTEntry* tte) const;
 
 private:
-  size_t size;
+  uint32_t hashMask;
-  TTCluster* entries;
+  TTEntry* table;
   uint8_t generation; // Size must be not bigger then TTEntry::generation8
 };
 
@@ -119,9 +108,9 @@ extern TranspositionTable TT;
 /// a cluster given a position. The lowest order bits of the key are used to
 /// get the index of the cluster.
 
-inline TTEntry* TranspositionTable::first_entry(const Key posKey) const {
+inline TTEntry* TranspositionTable::first_entry(const Key key) const {
 
-  return entries[((uint32_t)posKey) & (size - 1)].data;
+  return table + ((uint32_t)key & hashMask);
 }
 
 

src/types.h

@@ -489,21 +489,4 @@ inline const std::string square_to_string(Square s) {
   return ch;
 }
 
-/// Our insertion sort implementation, works with pointers and iterators and is
-/// guaranteed to be stable, as is needed.
-template<typename T, typename K>
-void sort(K begin, K end)
-{
-  T tmp;
-  K p, q;
-
-  for (p = begin + 1; p < end; p++)
-  {
-      tmp = *p;
-      for (q = p; q != begin && *(q-1) < tmp; --q)
-          *q = *(q-1);
-      *q = tmp;
-  }
-}
-
 #endif // !defined(TYPES_H_INCLUDED)

src/uci.cpp

@@ -44,7 +44,7 @@ namespace {
 
   void set_option(istringstream& up);
   void set_position(Position& pos, istringstream& up);
-  void go(Position& pos, istringstream& up);
+  void go(const Position& pos, istringstream& up);
 }
 
 
@@ -182,7 +182,7 @@ namespace {
   // the thinking time and other parameters from the input string, and starts
   // the search.
 
-  void go(Position& pos, istringstream& is) {
+  void go(const Position& pos, istringstream& is) {
 
     Search::LimitsType limits;
     vector<Move> searchMoves;