Use a Direction enum for Square deltas

Currently the NORTH/WEST/SOUTH/EAST values are of type Square, but conceptually they are not squares but directions. This patch separates these values into a Direction enum and overloads addition and subtraction to allow adding a Square to a Direction (to get a new Square).

I have also slightly trimmed the possible overloadings to improve type safety. For example, it would normally not make sense to add a Color to a Color or a Piece to a Piece, or to multiply or divide them by an integer. It would also normally not make sense to add a Square to a Square.

This is a non-functional change.

src/bitbase.cpp

@@ -111,7 +111,7 @@ namespace {
     ksq[WHITE] = Square((idx >>  0) & 0x3F);
     ksq[BLACK] = Square((idx >>  6) & 0x3F);
     us         = Color ((idx >> 12) & 0x01);
-    psq        = make_square(File((idx >> 13) & 0x3), RANK_7 - Rank((idx >> 15) & 0x7));
+    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
     if (   distance(ksq[WHITE], ksq[BLACK]) <= 1

src/bitboard.cpp

@@ -54,7 +54,7 @@ namespace {
   Bitboard RookTable[0x19000];  // To store rook attacks
   Bitboard BishopTable[0x1480]; // To store bishop attacks
 
-  void init_magics(Bitboard table[], Magic magics[], Square deltas[]);
+  void init_magics(Bitboard table[], Magic magics[], Direction directions[]);
 
   // bsf_index() returns the index into BSFTable[] to look up the bitscan. Uses
   // Matt Taylor's folding for 32 bit case, extended to 64 bit by Kim Walisch.
@@ -188,7 +188,7 @@ void Bitboards::init() {
           for (Square s = SQ_A1; s <= SQ_H8; ++s)
               for (int i = 0; steps[pt][i]; ++i)
               {
-                  Square to = s + Square(c == WHITE ? steps[pt][i] : -steps[pt][i]);
+                  Square to = s + Direction(c == WHITE ? steps[pt][i] : -steps[pt][i]);
 
                   if (is_ok(to) && distance(s, to) < 3)
                   {
@@ -199,11 +199,11 @@ void Bitboards::init() {
                   }
               }
 
-  Square RookDeltas[] = { NORTH,  EAST,  SOUTH,  WEST };
+  Direction RookDirections[] = { NORTH,  EAST,  SOUTH,  WEST };
-  Square BishopDeltas[] = { NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST };
+  Direction BishopDirections[] = { NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST };
 
-  init_magics(RookTable, RookMagics, RookDeltas);
+  init_magics(RookTable, RookMagics, RookDirections);
-  init_magics(BishopTable, BishopMagics, BishopDeltas);
+  init_magics(BishopTable, BishopMagics, BishopDirections);
 
   for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
   {
@@ -225,14 +225,14 @@ void Bitboards::init() {
 
 namespace {
 
-  Bitboard sliding_attack(Square deltas[], Square sq, Bitboard occupied) {
+  Bitboard sliding_attack(Direction directions[], Square sq, Bitboard occupied) {
 
     Bitboard attack = 0;
 
     for (int i = 0; i < 4; ++i)
-        for (Square s = sq + deltas[i];
+        for (Square s = sq + directions[i];
-             is_ok(s) && distance(s, s - deltas[i]) == 1;
+             is_ok(s) && distance(s, s - directions[i]) == 1;
-             s += deltas[i])
+             s += directions[i])
         {
             attack |= s;
 
@@ -249,7 +249,7 @@ namespace {
   // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
   // use the so called "fancy" approach.
 
-  void init_magics(Bitboard table[], Magic magics[], Square deltas[]) {
+  void init_magics(Bitboard table[], Magic magics[], Direction directions[]) {
 
     // Optimal PRNG seeds to pick the correct magics in the shortest time
     int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998,  5731, 95205, 104912, 17020 },
@@ -269,7 +269,7 @@ 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(deltas, s, 0) & ~edges;
+        m.mask  = sliding_attack(directions, s, 0) & ~edges;
         m.shift = (Is64Bit ? 64 : 32) - popcount(m.mask);
 
         // Set the offset for the attacks table of the square. We have individual
@@ -281,7 +281,7 @@ namespace {
         b = size = 0;
         do {
             occupancy[size] = b;
-            reference[size] = sliding_attack(deltas, s, b);
+            reference[size] = sliding_attack(directions, s, b);
 
             if (HasPext)
                 m.attacks[pext(b, m.mask)] = reference[size];

src/bitboard.h

@@ -152,7 +152,7 @@ inline Bitboard file_bb(Square s) {
 
 /// shift() moves a bitboard one step along direction D. Mainly for pawns
 
-template<Square D>
+template<Direction D>
 constexpr Bitboard shift(Bitboard b) {
   return  D == NORTH      ?  b             << 8 : D == SOUTH      ?  b             >> 8
         : D == NORTH_EAST ? (b & ~FileHBB) << 9 : D == SOUTH_EAST ? (b & ~FileHBB) >> 7

src/endgame.cpp

@@ -524,7 +524,7 @@ ScaleFactor Endgame<KRPKB>::operator()(const Position& pos) const {
       Square bsq = pos.square<BISHOP>(weakSide);
       Square psq = pos.square<PAWN>(strongSide);
       Rank rk = relative_rank(strongSide, psq);
-      Square push = pawn_push(strongSide);
+      Direction push = pawn_push(strongSide);
 
       // If the pawn is on the 5th rank and the pawn (currently) is on
       // the same color square as the bishop then there is a chance of

src/evaluate.cpp

@@ -254,8 +254,8 @@ namespace {
   void Evaluation<T>::initialize() {
 
     const Color     Them = (Us == WHITE ? BLACK : WHITE);
-    const Square Up   = (Us == WHITE ? NORTH : SOUTH);
+    const Direction Up   = (Us == WHITE ? NORTH : SOUTH);
-    const Square Down = (Us == WHITE ? SOUTH : NORTH);
+    const Direction Down = (Us == WHITE ? SOUTH : NORTH);
     const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
 
     // Find our pawns on the first two ranks, and those which are blocked
@@ -372,7 +372,7 @@ namespace {
                 && pos.is_chess960()
                 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
             {
-                Square d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
+                Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
                 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
                     score -= !pos.empty(s + d + pawn_push(Us))                ? TrappedBishopA1H1 * 4
                             : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
@@ -423,7 +423,7 @@ namespace {
   Score Evaluation<T>::evaluate_king() {
 
     const Color     Them = (Us == WHITE ? BLACK : WHITE);
-    const Square Up     = (Us == WHITE ? NORTH : SOUTH);
+    const Direction Up   = (Us == WHITE ? NORTH : SOUTH);
     const Bitboard  Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
                                         : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
 
@@ -531,9 +531,9 @@ namespace {
   Score Evaluation<T>::evaluate_threats() {
 
     const Color     Them     = (Us == WHITE ? BLACK      : WHITE);
-    const Square Up         = (Us == WHITE ? NORTH      : SOUTH);
+    const Direction Up       = (Us == WHITE ? NORTH      : SOUTH);
-    const Square Left       = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
+    const Direction Left     = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
-    const Square Right      = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
+    const Direction Right    = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
     const Bitboard  TRank3BB = (Us == WHITE ? Rank3BB    : Rank6BB);
 
     Bitboard b, weak, defended, stronglyProtected, safeThreats;
@@ -637,7 +637,7 @@ namespace {
   Score Evaluation<T>::evaluate_passed_pawns() {
 
     const Color     Them = (Us == WHITE ? BLACK : WHITE);
-    const Square Up  = (Us == WHITE ? NORTH : SOUTH);
+    const Direction Up   = (Us == WHITE ? NORTH : SOUTH);
 
     Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
     Score score = SCORE_ZERO;

src/movegen.cpp

@@ -42,7 +42,7 @@ namespace {
 
     assert(!pos.checkers());
 
-    const Square K = Chess960 ? kto > kfrom ? WEST : EAST
+    const Direction K = Chess960 ? kto > kfrom ? WEST : EAST
                                  : KingSide    ? WEST : EAST;
 
     for (Square s = kto; s != kfrom; s += K)
@@ -65,7 +65,7 @@ namespace {
   }
 
 
-  template<GenType Type, Square D>
+  template<GenType Type, Direction D>
   ExtMove* make_promotions(ExtMove* moveList, Square to, Square ksq) {
 
     if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
@@ -98,9 +98,9 @@ namespace {
     const Bitboard  TRank8BB = (Us == WHITE ? Rank8BB    : Rank1BB);
     const Bitboard  TRank7BB = (Us == WHITE ? Rank7BB    : Rank2BB);
     const Bitboard  TRank3BB = (Us == WHITE ? Rank3BB    : Rank6BB);
-    const Square   Up       = (Us == WHITE ? NORTH      : SOUTH);
+    const Direction Up       = (Us == WHITE ? NORTH      : SOUTH);
-    const Square   Right    = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
+    const Direction Right    = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
-    const Square   Left     = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
+    const Direction Left     = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
 
     Bitboard emptySquares;
 

src/pawns.cpp

@@ -95,9 +95,9 @@ namespace {
   Score evaluate(const Position& pos, Pawns::Entry* e) {
 
     const Color     Them  = (Us == WHITE ? BLACK      : WHITE);
-    const Square Up    = (Us == WHITE ? NORTH      : SOUTH);
+    const Direction Up    = (Us == WHITE ? NORTH      : SOUTH);
-    const Square Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
+    const Direction Right = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
-    const Square Left  = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
+    const Direction Left  = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
 
     Bitboard b, neighbours, stoppers, doubled, supported, phalanx;
     Bitboard lever, leverPush;
@@ -254,7 +254,7 @@ Value Entry::shelter_storm(const Position& pos, Square ksq) {
   Value safety = MaxSafetyBonus;
   File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
 
-  for (File f = center - File(1); f <= center + File(1); ++f)
+  for (File f = File(center - 1); f <= File(center + 1); ++f)
   {
       b = ourPawns & file_bb(f);
       Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
@@ -262,7 +262,7 @@ Value Entry::shelter_storm(const Position& pos, Square ksq) {
       b = theirPawns & file_bb(f);
       Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
 
-      int d = std::min(f, FILE_H - f);
+      int d = std::min(f, ~f);
       safety -=  ShelterWeakness[f == file_of(ksq)][d][rkUs]
                + StormDanger
                  [f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing  :

src/position.cpp

@@ -211,10 +211,10 @@ Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Th
   while ((ss >> token) && !isspace(token))
   {
       if (isdigit(token))
-          sq += Square(token - '0'); // Advance the given number of files
+          sq += (token - '0') * EAST; // Advance the given number of files
 
       else if (token == '/')
-          sq -= Square(16);
+          sq += 2 * SOUTH;
 
       else if ((idx = PieceToChar.find(token)) != string::npos)
       {
@@ -787,7 +787,7 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
       if (   (int(to) ^ int(from)) == 16
           && (attacks_from<PAWN>(to - pawn_push(us), us) & pieces(them, PAWN)))
       {
-          st->epSquare = (from + to) / 2;
+          st->epSquare = to - pawn_push(us);
           k ^= Zobrist::enpassant[file_of(st->epSquare)];
       }
 

src/psqt.cpp

@@ -116,7 +116,7 @@ void init() {
 
       for (Square s = SQ_A1; s <= SQ_H8; ++s)
       {
-          File f = std::min(file_of(s), FILE_H - file_of(s));
+          File f = std::min(file_of(s), ~file_of(s));
           psq[ pc][ s] = v + Bonus[pc][rank_of(s)][f];
           psq[~pc][~s] = -psq[pc][s];
       }

src/types.h

@@ -223,7 +223,7 @@ enum Depth : int {
 
 static_assert(!(ONE_PLY & (ONE_PLY - 1)), "ONE_PLY is not a power of 2");
 
-enum Square {
+enum Square : int {
   SQ_A1, SQ_B1, SQ_C1, SQ_D1, SQ_E1, SQ_F1, SQ_G1, SQ_H1,
   SQ_A2, SQ_B2, SQ_C2, SQ_D2, SQ_E2, SQ_F2, SQ_G2, SQ_H2,
   SQ_A3, SQ_B3, SQ_C3, SQ_D3, SQ_E3, SQ_F3, SQ_G3, SQ_H3,
@@ -234,8 +234,10 @@ enum Square {
   SQ_A8, SQ_B8, SQ_C8, SQ_D8, SQ_E8, SQ_F8, SQ_G8, SQ_H8,
   SQ_NONE,
 
-  SQUARE_NB = 64,
+  SQUARE_NB = 64
+};
 
+enum Direction : int {
   NORTH =  8,
   EAST  =  1,
   SOUTH = -NORTH,
@@ -284,31 +286,37 @@ constexpr T operator+(T d1, T d2) { return T(int(d1) + int(d2)); } \
 constexpr T operator-(T d1, T d2) { return T(int(d1) - int(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, T d2) { return d1 = d1 - d2; }         \
+inline T& operator-=(T& d1, T d2) { return d1 = d1 - d2; }
+
+#define ENABLE_INCR_OPERATORS_ON(T)                                \
+inline T& operator++(T& d) { return d = T(int(d) + 1); }           \
+inline T& operator--(T& d) { return d = T(int(d) - 1); }
 
 #define ENABLE_FULL_OPERATORS_ON(T)                                \
 ENABLE_BASE_OPERATORS_ON(T)                                        \
+ENABLE_INCR_OPERATORS_ON(T)                                        \
 constexpr T operator*(int i, T d) { return T(i * int(d)); }        \
 constexpr T operator*(T d, int i) { return T(int(d) * i); }        \
-inline T& operator++(T& d) { return d = T(int(d) + 1); }           \
-inline T& operator--(T& d) { return d = T(int(d) - 1); }           \
 constexpr T operator/(T d, int i) { return T(int(d) / i); }        \
 constexpr int operator/(T d1, T d2) { return int(d1) / int(d2); }  \
 inline T& operator*=(T& d, int i) { return d = T(int(d) * i); }    \
 inline T& operator/=(T& d, int i) { return d = T(int(d) / i); }
 
 ENABLE_FULL_OPERATORS_ON(Value)
-ENABLE_FULL_OPERATORS_ON(PieceType)
-ENABLE_FULL_OPERATORS_ON(Piece)
-ENABLE_FULL_OPERATORS_ON(Color)
 ENABLE_FULL_OPERATORS_ON(Depth)
-ENABLE_FULL_OPERATORS_ON(Square)
+ENABLE_FULL_OPERATORS_ON(Direction)
-ENABLE_FULL_OPERATORS_ON(File)
+
-ENABLE_FULL_OPERATORS_ON(Rank)
+ENABLE_INCR_OPERATORS_ON(PieceType)
+ENABLE_INCR_OPERATORS_ON(Piece)
+ENABLE_INCR_OPERATORS_ON(Color)
+ENABLE_INCR_OPERATORS_ON(Square)
+ENABLE_INCR_OPERATORS_ON(File)
+ENABLE_INCR_OPERATORS_ON(Rank)
 
 ENABLE_BASE_OPERATORS_ON(Score)
 
 #undef ENABLE_FULL_OPERATORS_ON
+#undef ENABLE_INCR_OPERATORS_ON
 #undef ENABLE_BASE_OPERATORS_ON
 
 /// Additional operators to add integers to a Value
@@ -317,6 +325,12 @@ 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
+inline Square operator+(Square s, Direction d) { return Square(int(s) + int(d)); }
+inline Square operator-(Square s, Direction d) { return Square(int(s) - int(d)); }
+inline Square& operator+=(Square &s, Direction d) { return s = s + d; }
+inline Square& operator-=(Square &s, Direction d) { return s = s - d; }
+
 /// Only declared but not defined. We don't want to multiply two scores due to
 /// a very high risk of overflow. So user should explicitly convert to integer.
 Score operator*(Score s1, Score s2) = delete;
@@ -346,6 +360,10 @@ constexpr Square operator~(Square s) {
   return Square(s ^ SQ_A8); // Vertical flip SQ_A1 -> SQ_A8
 }
 
+constexpr File operator~(File f) {
+  return File(f ^ FILE_H); // Horizontal flip FILE_A -> FILE_H
+}
+
 constexpr Piece operator~(Piece pc) {
   return Piece(pc ^ 8); // Swap color of piece B_KNIGHT -> W_KNIGHT
 }
@@ -408,7 +426,7 @@ inline bool opposite_colors(Square s1, Square s2) {
   return ((s >> 3) ^ s) & 1;
 }
 
-constexpr Square pawn_push(Color c) {
+constexpr Direction pawn_push(Color c) {
   return c == WHITE ? NORTH : SOUTH;
 }