small cleanups

closes https://github.com/official-stockfish/Stockfish/pull/2695

No functional change

src/Makefile

@@ -336,7 +336,7 @@ ifeq ($(pext),yes)
 	endif
 endif
 
-### 3.8 Link Time Optimization, it works since gcc 4.5 but not on mingw under Windows.
+### 3.8 Link Time Optimization
 ### This is a mix of compile and link time options because the lto link phase
 ### needs access to the optimization flags.
 ifeq ($(optimize),yes)

src/bitbase.cpp

@@ -108,25 +108,25 @@ namespace {
     stm        = Color ((idx >> 12) & 0x01);
     psq        = make_square(File((idx >> 13) & 0x3), Rank(RANK_7 - ((idx >> 15) & 0x7)));
 
-    // Check if two pieces are on the same square or if a king can be captured
+    // Invalid if two pieces are on the same square or if a king can be captured
     if (   distance(ksq[WHITE], ksq[BLACK]) <= 1
         || ksq[WHITE] == psq
         || ksq[BLACK] == psq
         || (stm == WHITE && (pawn_attacks_bb(WHITE, psq) & ksq[BLACK])))
         result = INVALID;
 
-    // Immediate win if a pawn can be promoted without getting captured
+    // Win if the pawn can be promoted without getting captured
     else if (   stm == WHITE
              && rank_of(psq) == RANK_7
-             && ksq[stm] != psq + NORTH
+             && ksq[WHITE] != psq + NORTH
-             && (    distance(ksq[~stm], psq + NORTH) > 1
+             && (    distance(ksq[BLACK], psq + NORTH) > 1
-                 || (attacks_bb<KING>(ksq[stm]) & (psq + NORTH))))
+                 || (distance(ksq[WHITE], psq + NORTH) == 1)))
         result = WIN;
 
-    // Immediate draw if it is a stalemate or a king captures undefended pawn
+    // Draw if it is stalemate or the black king can capture the pawn
     else if (   stm == BLACK
-             && (  !(attacks_bb<KING>(ksq[stm]) & ~(attacks_bb<KING>(ksq[~stm]) | pawn_attacks_bb(~stm, psq)))
+             && (  !(attacks_bb<KING>(ksq[BLACK]) & ~(attacks_bb<KING>(ksq[WHITE]) | pawn_attacks_bb(WHITE, psq)))
-                 || (attacks_bb<KING>(ksq[stm]) & psq & ~attacks_bb<KING>(ksq[~stm]))))
+                 || (attacks_bb<KING>(ksq[BLACK]) & ~attacks_bb<KING>(ksq[WHITE]) & psq)))
         result = DRAW;
 
     // Position will be classified later

src/bitboard.cpp

@@ -40,7 +40,7 @@ namespace {
   Bitboard RookTable[0x19000];  // To store rook attacks
   Bitboard BishopTable[0x1480]; // To store bishop attacks
 
-  void init_magics(Bitboard table[], Magic magics[], Direction directions[]);
+  void init_magics(PieceType pt, Bitboard table[], Magic magics[]);
 }
 
 
@@ -79,11 +79,8 @@ void Bitboards::init() {
       for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
           SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
 
-  Direction RookDirections[] = { NORTH, EAST, SOUTH, WEST };
+  init_magics(ROOK, RookTable, RookMagics);
-  Direction BishopDirections[] = { NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST };
+  init_magics(BISHOP, BishopTable, BishopMagics);
-
-  init_magics(RookTable, RookMagics, RookDirections);
-  init_magics(BishopTable, BishopMagics, BishopDirections);
 
   for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
   {
@@ -109,15 +106,17 @@ void Bitboards::init() {
 
 namespace {
 
-  Bitboard sliding_attack(Direction directions[], Square sq, Bitboard occupied) {
+  Bitboard sliding_attack(PieceType pt, Square sq, Bitboard occupied) {
 
     Bitboard attacks = 0;
+    Direction   RookDirections[4] = {NORTH, SOUTH, EAST, WEST};
+    Direction BishopDirections[4] = {NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST};
 
-    for (int i = 0; i < 4; ++i)
+    for(Direction d : (pt == ROOK ? RookDirections : BishopDirections))
     {
         Square s = sq;
-        while(safe_destination(s, directions[i]) && !(occupied & s))
+        while(safe_destination(s, d) && !(occupied & s))
-            attacks |= (s += directions[i]);
+            attacks |= (s += d);
     }
 
     return attacks;
@@ -129,7 +128,7 @@ namespace {
   // www.chessprogramming.org/Magic_Bitboards. In particular, here we use the so
   // called "fancy" approach.
 
-  void init_magics(Bitboard table[], Magic magics[], Direction directions[]) {
+  void init_magics(PieceType pt, Bitboard table[], Magic magics[]) {
 
     // Optimal PRNG seeds to pick the correct magics in the shortest time
     int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998,  5731, 95205, 104912, 17020 },
@@ -149,7 +148,7 @@ namespace {
         // the number of 1s of the mask. Hence we deduce the size of the shift to
         // apply to the 64 or 32 bits word to get the index.
         Magic& m = magics[s];
-        m.mask  = sliding_attack(directions, s, 0) & ~edges;
+        m.mask  = sliding_attack(pt, s, 0) & ~edges;
         m.shift = (Is64Bit ? 64 : 32) - popcount(m.mask);
 
         // Set the offset for the attacks table of the square. We have individual
@@ -161,7 +160,7 @@ namespace {
         b = size = 0;
         do {
             occupancy[size] = b;
-            reference[size] = sliding_attack(directions, s, b);
+            reference[size] = sliding_attack(pt, s, b);
 
             if (HasPext)
                 m.attacks[pext(b, m.mask)] = reference[size];

src/bitboard.h

@@ -253,7 +253,7 @@ inline Bitboard pawn_attack_span(Color c, Square s) {
 /// the given color and on the given square is a passed pawn.
 
 inline Bitboard passed_pawn_span(Color c, Square s) {
-  return forward_ranks_bb(c, s) & (adjacent_files_bb(s) | file_bb(s));
+  return pawn_attack_span(c, s) | forward_file_bb(c, s);
 }
 
 

src/evaluate.cpp

@@ -676,16 +676,15 @@ namespace {
   }
 
 
-  // Evaluation::space() computes the space evaluation for a given side. The
+  // Evaluation::space() computes a space evaluation for a given side, aiming to improve game
-  // space evaluation is a simple bonus based on the number of safe squares
+  // play in the opening. It is based on the number of safe squares on the 4 central files
-  // available for minor pieces on the central four files on ranks 2--4. Safe
+  // on ranks 2 to 4. Completely safe squares behind a friendly pawn are counted twice.
-  // squares one, two or three squares behind a friendly pawn are counted
+  // Finally, the space bonus is multiplied by a weight which decreases according to occupancy.
-  // twice. Finally, the space bonus is multiplied by a weight. The aim is to
-  // improve play on game opening.
 
   template<Tracing T> template<Color Us>
   Score Evaluation<T>::space() const {
 
+    // Early exit if, for example, both queens or 6 minor pieces have been exchanged
     if (pos.non_pawn_material() < SpaceThreshold)
         return SCORE_ZERO;
 

src/movepick.cpp

@@ -57,7 +57,7 @@ namespace {
 
 /// MovePicker constructor for the main search
 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh, const LowPlyHistory* lp,
-                       const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers, int pl)
+                       const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, const Move* killers, int pl)
            : pos(p), mainHistory(mh), lowPlyHistory(lp), captureHistory(cph), continuationHistory(ch),
              ttMove(ttm), refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d), ply(pl) {
 

src/movepick.h

@@ -88,9 +88,9 @@ enum StatsType { NoCaptures, Captures };
 /// the move's from and to squares, see www.chessprogramming.org/Butterfly_Boards
 typedef Stats<int16_t, 10692, COLOR_NB, int(SQUARE_NB) * int(SQUARE_NB)> ButterflyHistory;
 
-/// LowPlyHistory at higher depths records successful quiet moves on plies 0 to 3
+/// At higher depths LowPlyHistory records successful quiet moves near the root and quiet
-/// and quiet moves which are/were in the PV (ttPv)
+/// moves which are/were in the PV (ttPv)
-/// It get cleared with each new search and get filled during iterative deepening
+/// It is cleared with each new search and filled during iterative deepening
 constexpr int MAX_LPH = 4;
 typedef Stats<int16_t, 10692, MAX_LPH, int(SQUARE_NB) * int(SQUARE_NB)> LowPlyHistory;
 
@@ -133,7 +133,7 @@ public:
                                            const CapturePieceToHistory*,
                                            const PieceToHistory**,
                                            Move,
-                                           Move*,
+                                           const Move*,
                                            int);
   Move next_move(bool skipQuiets = false);
 

src/pawns.cpp

@@ -196,7 +196,7 @@ Entry* probe(const Position& pos) {
 /// penalty for a king, looking at the king file and the two closest files.
 
 template<Color Us>
-Score Entry::evaluate_shelter(const Position& pos, Square ksq) {
+Score Entry::evaluate_shelter(const Position& pos, Square ksq) const {
 
   constexpr Color Them = ~Us;
 

src/pawns.h

@@ -50,7 +50,7 @@ struct Entry {
   Score do_king_safety(const Position& pos);
 
   template<Color Us>
-  Score evaluate_shelter(const Position& pos, Square ksq);
+  Score evaluate_shelter(const Position& pos, Square ksq) const;
 
   Key key;
   Score scores[COLOR_NB];

src/psqt.cpp

@@ -106,7 +106,7 @@ Score psq[PIECE_NB][SQUARE_NB];
 // tables are initialized by flipping and changing the sign of the white scores.
 void init() {
 
-  for (Piece pc = W_PAWN; pc <= W_KING; ++pc)
+  for (Piece pc : {W_PAWN, W_KNIGHT, W_BISHOP, W_ROOK, W_QUEEN, W_KING})
   {
       Score score = make_score(PieceValue[MG][pc], PieceValue[EG][pc]);
 

src/search.cpp

@@ -670,7 +670,7 @@ namespace {
     ttPv = PvNode || (ttHit && tte->is_pv());
     formerPv = ttPv && !PvNode;
 
-    if (ttPv && depth > 12 && ss->ply - 1 < MAX_LPH && !pos.captured_piece() && is_ok((ss-1)->currentMove))
+    if (ttPv && depth > 12 && ss->ply - 1 < MAX_LPH && !priorCapture && is_ok((ss-1)->currentMove))
         thisThread->lowPlyHistory[ss->ply - 1][from_to((ss-1)->currentMove)] << stat_bonus(depth - 5);
 
     // thisThread->ttHitAverage can be used to approximate the running average of ttHit

src/syzygy/tbprobe.cpp

@@ -1200,7 +1200,7 @@ WDLScore search(Position& pos, ProbeState* result) {
     auto moveList = MoveList<LEGAL>(pos);
     size_t totalCount = moveList.size(), moveCount = 0;
 
-    for (const Move& move : moveList)
+    for (const Move move : moveList)
     {
         if (   !pos.capture(move)
             && (!CheckZeroingMoves || type_of(pos.moved_piece(move)) != PAWN))
@@ -1362,7 +1362,7 @@ void Tablebases::init(const std::string& paths) {
             LeadPawnsSize[leadPawnsCnt][f] = idx;
         }
 
-    // Add entries in TB tables if the corresponding ".rtbw" file exsists
+    // Add entries in TB tables if the corresponding ".rtbw" file exists
     for (PieceType p1 = PAWN; p1 < KING; ++p1) {
         TBTables.add({KING, p1, KING});
 
@@ -1469,7 +1469,7 @@ int Tablebases::probe_dtz(Position& pos, ProbeState* result) {
     StateInfo st;
     int minDTZ = 0xFFFF;
 
-    for (const Move& move : MoveList<LEGAL>(pos))
+    for (const Move move : MoveList<LEGAL>(pos))
     {
         bool zeroing = pos.capture(move) || type_of(pos.moved_piece(move)) == PAWN;
 

src/timeman.cpp

@@ -79,7 +79,7 @@ void TimeManagement::init(Search::LimitsType& limits, Color us, int ply) {
   {
       opt_scale = std::min(0.008 + std::pow(ply + 3.0, 0.5) / 250.0,
                            0.2 * limits.time[us] / double(timeLeft));
-      max_scale = 4 + std::min(36, ply) / 12.0;
+      max_scale = std::min(7.0, 4.0 + ply / 12.0);
   }
 
   // x moves in y seconds (+ z increment)

src/types.h

@@ -40,7 +40,6 @@
 
 #include <cassert>
 #include <cctype>
-#include <climits>
 #include <cstdint>
 #include <cstdlib>
 #include <algorithm>
@@ -214,7 +213,6 @@ constexpr Value PieceValue[PHASE_NB][PIECE_NB] = {
 typedef int Depth;
 
 enum : int {
-
   DEPTH_QS_CHECKS     =  0,
   DEPTH_QS_NO_CHECKS  = -1,
   DEPTH_QS_RECAPTURES = -5,
@@ -282,11 +280,11 @@ inline Value mg_value(Score s) {
 }
 
 #define ENABLE_BASE_OPERATORS_ON(T)                                \
-constexpr T operator+(T d1, T d2) { return T(int(d1) + int(d2)); } \
+constexpr T operator+(T d1, int d2) { return T(int(d1) + d2); } \
-constexpr T operator-(T d1, T d2) { return T(int(d1) - int(d2)); } \
+constexpr T operator-(T d1, int d2) { return T(int(d1) - d2); } \
 constexpr T operator-(T d) { return T(-int(d)); }                  \
-inline T& operator+=(T& d1, T d2) { return d1 = d1 + d2; }         \
+inline T& operator+=(T& d1, int d2) { return d1 = d1 + d2; }         \
-inline T& operator-=(T& d1, T d2) { return d1 = d1 - d2; }
+inline T& operator-=(T& d1, int d2) { return d1 = d1 - d2; }
 
 #define ENABLE_INCR_OPERATORS_ON(T)                                \
 inline T& operator++(T& d) { return d = T(int(d) + 1); }           \
@@ -305,7 +303,6 @@ ENABLE_FULL_OPERATORS_ON(Value)
 ENABLE_FULL_OPERATORS_ON(Direction)
 
 ENABLE_INCR_OPERATORS_ON(PieceType)
-ENABLE_INCR_OPERATORS_ON(Piece)
 ENABLE_INCR_OPERATORS_ON(Square)
 ENABLE_INCR_OPERATORS_ON(File)
 ENABLE_INCR_OPERATORS_ON(Rank)
@@ -316,12 +313,6 @@ ENABLE_BASE_OPERATORS_ON(Score)
 #undef ENABLE_INCR_OPERATORS_ON
 #undef ENABLE_BASE_OPERATORS_ON
 
-/// Additional operators to add integers to a Value
-constexpr Value operator+(Value v, int i) { return Value(int(v) + i); }
-constexpr Value operator-(Value v, int i) { return Value(int(v) - i); }
-inline Value& operator+=(Value& v, int i) { return v = v + i; }
-inline Value& operator-=(Value& v, int i) { return v = v - i; }
-
 /// Additional operators to add a Direction to a Square
 constexpr Square operator+(Square s, Direction d) { return Square(int(s) + int(d)); }
 constexpr Square operator-(Square s, Direction d) { return Square(int(s) - int(d)); }