Tidy up

No functional change

Closes #1148

src/bitboard.cpp

@@ -30,11 +30,11 @@ Bitboard SquareBB[SQUARE_NB];
 Bitboard FileBB[FILE_NB];
 Bitboard RankBB[RANK_NB];
 Bitboard AdjacentFilesBB[FILE_NB];
-Bitboard InFrontBB[COLOR_NB][RANK_NB];
+Bitboard ForwardRanksBB[COLOR_NB][RANK_NB];
 Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
 Bitboard LineBB[SQUARE_NB][SQUARE_NB];
 Bitboard DistanceRingBB[SQUARE_NB][8];
-Bitboard ForwardBB[COLOR_NB][SQUARE_NB];
+Bitboard ForwardFileBB[COLOR_NB][SQUARE_NB];
 Bitboard PassedPawnMask[COLOR_NB][SQUARE_NB];
 Bitboard PawnAttackSpan[COLOR_NB][SQUARE_NB];
 Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
@@ -163,14 +163,14 @@ void Bitboards::init() {
       AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
 
   for (Rank r = RANK_1; r < RANK_8; ++r)
-      InFrontBB[WHITE][r] = ~(InFrontBB[BLACK][r + 1] = InFrontBB[BLACK][r] | RankBB[r]);
+      ForwardRanksBB[WHITE][r] = ~(ForwardRanksBB[BLACK][r + 1] = ForwardRanksBB[BLACK][r] | RankBB[r]);
 
   for (Color c = WHITE; c <= BLACK; ++c)
       for (Square s = SQ_A1; s <= SQ_H8; ++s)
       {
-          ForwardBB[c][s]      = InFrontBB[c][rank_of(s)] & FileBB[file_of(s)];
+          ForwardFileBB [c][s] = ForwardRanksBB[c][rank_of(s)] & FileBB[file_of(s)];
-          PawnAttackSpan[c][s] = InFrontBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
+          PawnAttackSpan[c][s] = ForwardRanksBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
-          PassedPawnMask[c][s] = ForwardBB[c][s] | PawnAttackSpan[c][s];
+          PassedPawnMask[c][s] = ForwardFileBB [c][s] | PawnAttackSpan[c][s];
       }
 
   for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)

src/bitboard.h

@@ -65,11 +65,11 @@ extern Bitboard SquareBB[SQUARE_NB];
 extern Bitboard FileBB[FILE_NB];
 extern Bitboard RankBB[RANK_NB];
 extern Bitboard AdjacentFilesBB[FILE_NB];
-extern Bitboard InFrontBB[COLOR_NB][RANK_NB];
+extern Bitboard ForwardRanksBB[COLOR_NB][RANK_NB];
 extern Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
 extern Bitboard LineBB[SQUARE_NB][SQUARE_NB];
 extern Bitboard DistanceRingBB[SQUARE_NB][8];
-extern Bitboard ForwardBB[COLOR_NB][SQUARE_NB];
+extern Bitboard ForwardFileBB[COLOR_NB][SQUARE_NB];
 extern Bitboard PassedPawnMask[COLOR_NB][SQUARE_NB];
 extern Bitboard PawnAttackSpan[COLOR_NB][SQUARE_NB];
 extern Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
@@ -179,28 +179,28 @@ inline Bitboard between_bb(Square s1, Square s2) {
 }
 
 
-/// in_front_bb() returns a bitboard representing all the squares on all the ranks
+/// forward_ranks_bb() returns a bitboard representing all the squares on all the ranks
 /// in front of the given one, from the point of view of the given color. For
-/// instance, in_front_bb(BLACK, RANK_3) will return the squares on ranks 1 and 2.
+/// instance, forward_ranks_bb(BLACK, SQ_D3) will return the 16 squares on ranks 1 and 2.
 
-inline Bitboard in_front_bb(Color c, Rank r) {
+inline Bitboard forward_ranks_bb(Color c, Square s) {
-  return InFrontBB[c][r];
+  return ForwardRanksBB[c][rank_of(s)];
 }
 
 
-/// forward_bb() returns a bitboard representing all the squares along the line
+/// forward_file_bb() returns a bitboard representing all the squares along the line
 /// in front of the given one, from the point of view of the given color:
-///        ForwardBB[c][s] = in_front_bb(c, rank_of(s)) & file_bb(s)
+///      ForwardFileBB[c][s] = forward_ranks_bb(c, s) & file_bb(s)
 
-inline Bitboard forward_bb(Color c, Square s) {
+inline Bitboard forward_file_bb(Color c, Square s) {
-  return ForwardBB[c][s];
+  return ForwardFileBB[c][s];
 }
 
 
 /// pawn_attack_span() returns a bitboard representing all the squares that can be
 /// attacked by a pawn of the given color when it moves along its file, starting
 /// from the given square:
-///       PawnAttackSpan[c][s] = in_front_bb(c, rank_of(s)) & adjacent_files_bb(file_of(s));
+///      PawnAttackSpan[c][s] = forward_ranks_bb(c, s) & adjacent_files_bb(file_of(s));
 
 inline Bitboard pawn_attack_span(Color c, Square s) {
   return PawnAttackSpan[c][s];
@@ -209,7 +209,7 @@ inline Bitboard pawn_attack_span(Color c, Square s) {
 
 /// passed_pawn_mask() returns a bitboard mask which can be used to test if a
 /// pawn of the given color and on the given square is a passed pawn:
-///       PassedPawnMask[c][s] = pawn_attack_span(c, s) | forward_bb(c, s)
+///      PassedPawnMask[c][s] = pawn_attack_span(c, s) | forward_file_bb(c, s)
 
 inline Bitboard passed_pawn_mask(Color c, Square s) {
   return PassedPawnMask[c][s];

src/endgame.cpp

@@ -598,7 +598,7 @@ ScaleFactor Endgame<KPsK>::operator()(const Position& pos) const {
 
   // If all pawns are ahead of the king, on a single rook file and
   // the king is within one file of the pawns, it's a draw.
-  if (   !(pawns & ~in_front_bb(weakSide, rank_of(ksq)))
+  if (   !(pawns & ~forward_ranks_bb(weakSide, ksq))
       && !((pawns & ~FileABB) && (pawns & ~FileHBB))
       &&  distance<File>(ksq, lsb(pawns)) <= 1)
       return SCALE_FACTOR_DRAW;
@@ -645,7 +645,7 @@ ScaleFactor Endgame<KBPKB>::operator()(const Position& pos) const {
       if (relative_rank(strongSide, pawnSq) <= RANK_5)
           return SCALE_FACTOR_DRAW;
 
-      Bitboard path = forward_bb(strongSide, pawnSq);
+      Bitboard path = forward_file_bb(strongSide, pawnSq);
 
       if (path & pos.pieces(weakSide, KING))
           return SCALE_FACTOR_DRAW;
@@ -780,7 +780,7 @@ ScaleFactor Endgame<KNPKB>::operator()(const Position& pos) const {
 
   // King needs to get close to promoting pawn to prevent knight from blocking.
   // Rules for this are very tricky, so just approximate.
-  if (forward_bb(strongSide, pawnSq) & pos.attacks_from<BISHOP>(bishopSq))
+  if (forward_file_bb(strongSide, pawnSq) & pos.attacks_from<BISHOP>(bishopSq))
       return ScaleFactor(distance(weakKingSq, pawnSq));
 
   return SCALE_FACTOR_NONE;

src/evaluate.cpp

@@ -88,7 +88,7 @@ namespace {
     template<Color Us> void initialize();
     template<Color Us> Score evaluate_king();
     template<Color Us> Score evaluate_threats();
-    template<Color Us> Score evaluate_passer_pawns();
+    template<Color Us> Score evaluate_passed_pawns();
     template<Color Us> Score evaluate_space();
     template<Color Us, PieceType Pt> Score evaluate_pieces();
     ScaleFactor evaluate_scale_factor(Value eg);
@@ -416,7 +416,7 @@ namespace {
                                        : ~Bitboard(0) ^ Rank1BB ^ Rank2BB ^ Rank3BB);
 
     const Square ksq = pos.square<KING>(Us);
-    Bitboard undefended, b, b1, b2, safe, other;
+    Bitboard kingOnlyDefended, b, b1, b2, safe, other;
     int kingDanger;
 
     // King shelter and enemy pawns storm
@@ -426,9 +426,9 @@ namespace {
     if (kingAttackersCount[Them] > (1 - pos.count<QUEEN>(Them)))
     {
         // Find the attacked squares which are defended only by our king...
-        undefended =   attackedBy[Them][ALL_PIECES]
+        kingOnlyDefended =   attackedBy[Them][ALL_PIECES]
-                    &  attackedBy[Us][KING]
+                          &  attackedBy[Us][KING]
-                    & ~attackedBy2[Us];
+                          & ~attackedBy2[Us];
 
         // ... and those which are not defended at all in the larger king ring
         b =  attackedBy[Them][ALL_PIECES] & ~attackedBy[Us][ALL_PIECES]
@@ -437,11 +437,11 @@ namespace {
         // Initialize the 'kingDanger' variable, which will be transformed
         // later into a king danger score. The initial value is based on the
         // number and types of the enemy's attacking pieces, the number of
-        // attacked and undefended squares around our king and the quality of
+        // attacked and weak squares around our king, the absence of queen and
-        // the pawn shelter (current 'score' value).
+        // the quality of the pawn shelter (current 'score' value).
         kingDanger =        kingAttackersCount[Them] * kingAttackersWeight[Them]
                     + 102 * kingAdjacentZoneAttacksCount[Them]
-                    + 201 * popcount(undefended)
+                    + 201 * popcount(kingOnlyDefended)
                     + 143 * (popcount(b) + !!pos.pinned_pieces(Us))
                     - 848 * !pos.count<QUEEN>(Them)
                     -   9 * mg_value(score) / 8
@@ -449,7 +449,7 @@ namespace {
 
         // Analyse the safe enemy's checks which are possible on next move
         safe  = ~pos.pieces(Them);
-        safe &= ~attackedBy[Us][ALL_PIECES] | (undefended & attackedBy2[Them]);
+        safe &= ~attackedBy[Us][ALL_PIECES] | (kingOnlyDefended & attackedBy2[Them]);
 
         b1 = pos.attacks_from<  ROOK>(ksq);
         b2 = pos.attacks_from<BISHOP>(ksq);
@@ -532,8 +532,7 @@ namespace {
     const Square Up         = (Us == WHITE ? NORTH      : SOUTH);
     const Square Left       = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
     const Square Right      = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
-    const Bitboard TRank2BB = (Us == WHITE ? Rank2BB    : Rank7BB);
+    const Bitboard TRank3BB = (Us == WHITE ? Rank3BB    : Rank6BB);
-    const Bitboard TRank7BB = (Us == WHITE ? Rank7BB    : Rank2BB);
 
     Bitboard b, weak, defended, stronglyProtected, safeThreats;
     Score score = SCORE_ZERO;
@@ -596,14 +595,15 @@ namespace {
             score += ThreatByKing[more_than_one(b)];
     }
 
-    // Bonus if some pawns can safely push and attack an enemy piece
+    // Find squares where our pawns can push on the next move
-    b = pos.pieces(Us, PAWN) & ~TRank7BB;
+    b  = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
-    b = shift<Up>(b | (shift<Up>(b & TRank2BB) & ~pos.pieces()));
+    b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
 
-    b &=  ~pos.pieces()
+    // Keep only the squares which are not completely unsafe
-        & ~attackedBy[Them][PAWN]
+    b &= ~attackedBy[Them][PAWN]
         & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
 
+    // Add a bonus for each new pawn threats from those squares
     b =  (shift<Left>(b) | shift<Right>(b))
        &  pos.pieces(Them)
        & ~attackedBy[Us][PAWN];
@@ -617,13 +617,14 @@ namespace {
   }
 
 
-  // evaluate_passer_pawns() evaluates the passed pawns and candidate passed
+  // evaluate_passed_pawns() evaluates the passed pawns and candidate passed
   // pawns of the given color.
 
   template<Tracing T>  template<Color Us>
-  Score Evaluation<T>::evaluate_passer_pawns() {
+  Score Evaluation<T>::evaluate_passed_pawns() {
 
     const Color Them = (Us == WHITE ? BLACK : WHITE);
+    const Square Up  = (Us == WHITE ? NORTH : SOUTH);
 
     Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
     Score score = SCORE_ZERO;
@@ -634,9 +635,9 @@ namespace {
     {
         Square s = pop_lsb(&b);
 
-        assert(!(pos.pieces(Them, PAWN) & forward_bb(Us, s + pawn_push(Us))));
+        assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
 
-        bb = forward_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
+        bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
         score -= HinderPassedPawn * popcount(bb);
 
         int r = relative_rank(Us, s) - RANK_2;
@@ -646,7 +647,7 @@ namespace {
 
         if (rr)
         {
-            Square blockSq = s + pawn_push(Us);
+            Square blockSq = s + Up;
 
             // Adjust bonus based on the king's proximity
             ebonus +=  distance(pos.square<KING>(Them), blockSq) * 5 * rr
@@ -654,7 +655,7 @@ namespace {
 
             // If blockSq is not the queening square then consider also a second push
             if (relative_rank(Us, blockSq) != RANK_8)
-                ebonus -= distance(pos.square<KING>(Us), blockSq + pawn_push(Us)) * rr;
+                ebonus -= distance(pos.square<KING>(Us), blockSq + Up) * rr;
 
             // If the pawn is free to advance, then increase the bonus
             if (pos.empty(blockSq))
@@ -662,9 +663,9 @@ namespace {
                 // If there is a rook or queen attacking/defending the pawn from behind,
                 // consider all the squaresToQueen. Otherwise consider only the squares
                 // in the pawn's path attacked or occupied by the enemy.
-                defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
+                defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
 
-                bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
+                bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
 
                 if (!(pos.pieces(Us) & bb))
                     defendedSquares &= attackedBy[Us][ALL_PIECES];
@@ -692,7 +693,7 @@ namespace {
 
         // Scale down bonus for candidate passers which need more than one
         // pawn push to become passed or have a pawn in front of them.
-        if (!pos.pawn_passed(Us, s + pawn_push(Us)) || (pos.pieces(PAWN) & forward_bb(Us, s)))
+        if (!pos.pawn_passed(Us, s + Up) || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
             mbonus /= 2, ebonus /= 2;
 
         score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
@@ -852,8 +853,8 @@ namespace {
     score +=  evaluate_threats<WHITE>()
             - evaluate_threats<BLACK>();
 
-    score +=  evaluate_passer_pawns<WHITE>()
+    score +=  evaluate_passed_pawns<WHITE>()
-            - evaluate_passer_pawns<BLACK>();
+            - evaluate_passed_pawns<BLACK>();
 
     if (pos.non_pawn_material() >= SpaceThreshold)
         score +=  evaluate_space<WHITE>()

src/pawns.cpp

@@ -126,7 +126,7 @@ namespace {
         e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s);
 
         // Flag the pawn
-        opposed    = theirPawns & forward_bb(Us, s);
+        opposed    = theirPawns & forward_file_bb(Us, s);
         stoppers   = theirPawns & passed_pawn_mask(Us, s);
         lever      = theirPawns & PawnAttacks[Us][s];
         leverPush  = theirPawns & PawnAttacks[Us][s + Up];
@@ -158,7 +158,7 @@ namespace {
         // which could become passed after one or two pawn pushes when are
         // not attacked more times than defended.
         if (   !(stoppers ^ lever ^ leverPush)
-            && !(ourPawns & forward_bb(Us, s))
+            && !(ourPawns & forward_file_bb(Us, s))
             && popcount(supported) >= popcount(lever)
             && popcount(phalanx)   >= popcount(leverPush))
             e->passedPawns[Us] |= s;
@@ -250,7 +250,7 @@ Value Entry::shelter_storm(const Position& pos, Square ksq) {
 
   enum { BlockedByKing, Unopposed, BlockedByPawn, Unblocked };
 
-  Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
+  Bitboard b = pos.pieces(PAWN) & (forward_ranks_bb(Us, ksq) | rank_bb(ksq));
   Bitboard ourPawns = b & pos.pieces(Us);
   Bitboard theirPawns = b & pos.pieces(Them);
   Value safety = MaxSafetyBonus;
@@ -261,7 +261,7 @@ Value Entry::shelter_storm(const Position& pos, Square ksq) {
       b = ourPawns & file_bb(f);
       Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
 
-      b  = theirPawns & file_bb(f);
+      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);