Retire one implementation of pop_lsb()

We have two implementations that are equivalent,
so retire one.

Plus usual tidy up of comments and code reshuffle.

No functional change.

src/bitbase.cpp

@@ -71,7 +71,7 @@ namespace {
 } // namespace
 
 
-bool Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color us) {
+bool Bitbases::probe(Square wksq, Square wpsq, Square bksq, Color us) {
 
   assert(file_of(wpsq) <= FILE_D);
 
@@ -80,7 +80,7 @@ bool Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color us) {
 }
 
 
-void Bitbases::init_kpk() {
+void Bitbases::init() {
 
   unsigned idx, repeat = 1;
   std::vector<KPKPosition> db;

src/bitboard.cpp

@@ -24,15 +24,17 @@
 #include "bitcount.h"
 #include "misc.h"
 
-Bitboard RookMasks[SQUARE_NB];
+int SquareDistance[SQUARE_NB][SQUARE_NB];
-Bitboard RookMagics[SQUARE_NB];
-Bitboard* RookAttacks[SQUARE_NB];
-unsigned RookShifts[SQUARE_NB];
 
-Bitboard BishopMasks[SQUARE_NB];
+Bitboard  RookMasks  [SQUARE_NB];
-Bitboard BishopMagics[SQUARE_NB];
+Bitboard  RookMagics [SQUARE_NB];
+Bitboard* RookAttacks[SQUARE_NB];
+unsigned  RookShifts [SQUARE_NB];
+
+Bitboard  BishopMasks  [SQUARE_NB];
+Bitboard  BishopMagics [SQUARE_NB];
 Bitboard* BishopAttacks[SQUARE_NB];
-unsigned BishopShifts[SQUARE_NB];
+unsigned  BishopShifts [SQUARE_NB];
 
 Bitboard SquareBB[SQUARE_NB];
 Bitboard FileBB[FILE_NB];
@@ -42,51 +44,44 @@ Bitboard InFrontBB[COLOR_NB][RANK_NB];
 Bitboard StepAttacksBB[PIECE_NB][SQUARE_NB];
 Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
 Bitboard LineBB[SQUARE_NB][SQUARE_NB];
-Bitboard DistanceRingsBB[SQUARE_NB][8];
+Bitboard DistanceRingBB[SQUARE_NB][8];
 Bitboard ForwardBB[COLOR_NB][SQUARE_NB];
 Bitboard PassedPawnMask[COLOR_NB][SQUARE_NB];
 Bitboard PawnAttackSpan[COLOR_NB][SQUARE_NB];
 Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
 
-int SquareDistance[SQUARE_NB][SQUARE_NB];
-
 namespace {
 
   // De Bruijn sequences. See chessprogramming.wikispaces.com/BitScan
-  const uint64_t DeBruijn_64 = 0x3F79D71B4CB0A89ULL;
+  const uint64_t DeBruijn64 = 0x3F79D71B4CB0A89ULL;
-  const uint32_t DeBruijn_32 = 0x783A9B23;
+  const uint32_t DeBruijn32 = 0x783A9B23;
 
-  int MS1BTable[256];
+  int MS1BTable[256];           // To implement software msb()
-  Square BSFTable[SQUARE_NB];
+  Square BSFTable[SQUARE_NB];   // To implement software bitscan
-  Bitboard RookTable[0x19000];  // Storage space for rook attacks
+  Bitboard RookTable[0x19000];  // To store rook attacks
-  Bitboard BishopTable[0x1480]; // Storage space for bishop attacks
+  Bitboard BishopTable[0x1480]; // To store bishop attacks
 
   typedef unsigned (Fn)(Square, Bitboard);
 
   void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
                    Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
 
-  FORCE_INLINE unsigned bsf_index(Bitboard b) {
+  // 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.
 
-    // Matt Taylor's folding for 32 bit systems, extended to 64 bits by Kim Walisch
+  FORCE_INLINE unsigned bsf_index(Bitboard b) {
-    b ^= (b - 1);
+    b ^= b - 1;
-    return Is64Bit ? (b * DeBruijn_64) >> 58
+    return Is64Bit ? (b * DeBruijn64) >> 58
-                   : ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn_32) >> 26;
+                   : ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn32) >> 26;
   }
 }
 
-/// lsb()/msb() finds the least/most significant bit in a non-zero bitboard.
-/// pop_lsb() finds and clears the least significant bit in a non-zero bitboard.
-
 #ifndef USE_BSFQ
 
-Square lsb(Bitboard b) { return BSFTable[bsf_index(b)]; }
+/// Software fall-back of lsb() and msb() for CPU lacking hardware support
 
-Square pop_lsb(Bitboard* b) {
+Square lsb(Bitboard b) {
-
+  return BSFTable[bsf_index(b)];
-  Bitboard bb = *b;
-  *b = bb & (bb - 1);
-  return BSFTable[bsf_index(bb)];
 }
 
 Square msb(Bitboard b) {
@@ -120,8 +115,8 @@ Square msb(Bitboard b) {
 #endif // ifndef USE_BSFQ
 
 
-/// Bitboards::pretty() returns an ASCII representation of a bitboard to be
+/// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
-/// printed to standard output. This is sometimes useful for debugging.
+/// to be printed to standard output. Useful for debugging.
 
 const std::string Bitboards::pretty(Bitboard b) {
 
@@ -178,7 +173,7 @@ void Bitboards::init() {
           if (s1 != s2)
           {
               SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
-              DistanceRingsBB[s1][SquareDistance[s1][s2] - 1] |= s2;
+              DistanceRingBB[s1][SquareDistance[s1][s2] - 1] |= s2;
           }
 
   int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },

src/bitboard.h

@@ -25,6 +25,13 @@
 
 #include "types.h"
 
+namespace Bitbases {
+
+void init();
+bool probe(Square wksq, Square wpsq, Square bksq, Color us);
+
+}
+
 namespace Bitboards {
 
 void init();
@@ -32,12 +39,7 @@ const std::string pretty(Bitboard b);
 
 }
 
-namespace Bitbases {
+const Bitboard DarkSquares = 0xAA55AA55AA55AA55ULL;
-
-void init_kpk();
-bool probe_kpk(Square wksq, Square wpsq, Square bksq, Color us);
-
-}
 
 const Bitboard FileABB = 0x0101010101010101ULL;
 const Bitboard FileBBB = FileABB << 1;
@@ -57,15 +59,17 @@ const Bitboard Rank6BB = Rank1BB << (8 * 5);
 const Bitboard Rank7BB = Rank1BB << (8 * 6);
 const Bitboard Rank8BB = Rank1BB << (8 * 7);
 
-extern Bitboard RookMasks[SQUARE_NB];
+extern int SquareDistance[SQUARE_NB][SQUARE_NB];
-extern Bitboard RookMagics[SQUARE_NB];
-extern Bitboard* RookAttacks[SQUARE_NB];
-extern unsigned RookShifts[SQUARE_NB];
 
-extern Bitboard BishopMasks[SQUARE_NB];
+extern Bitboard  RookMasks  [SQUARE_NB];
-extern Bitboard BishopMagics[SQUARE_NB];
+extern Bitboard  RookMagics [SQUARE_NB];
+extern Bitboard* RookAttacks[SQUARE_NB];
+extern unsigned  RookShifts [SQUARE_NB];
+
+extern Bitboard  BishopMasks  [SQUARE_NB];
+extern Bitboard  BishopMagics [SQUARE_NB];
 extern Bitboard* BishopAttacks[SQUARE_NB];
-extern unsigned BishopShifts[SQUARE_NB];
+extern unsigned  BishopShifts [SQUARE_NB];
 
 extern Bitboard SquareBB[SQUARE_NB];
 extern Bitboard FileBB[FILE_NB];
@@ -75,15 +79,12 @@ extern Bitboard InFrontBB[COLOR_NB][RANK_NB];
 extern Bitboard StepAttacksBB[PIECE_NB][SQUARE_NB];
 extern Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
 extern Bitboard LineBB[SQUARE_NB][SQUARE_NB];
-extern Bitboard DistanceRingsBB[SQUARE_NB][8];
+extern Bitboard DistanceRingBB[SQUARE_NB][8];
 extern Bitboard ForwardBB[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];
 
-extern int SquareDistance[SQUARE_NB][SQUARE_NB];
-
-const Bitboard DarkSquares = 0xAA55AA55AA55AA55ULL;
 
 /// Overloads of bitwise operators between a Bitboard and a Square for testing
 /// whether a given bit is set in a bitboard, and for setting and clearing bits.
@@ -92,14 +93,6 @@ inline Bitboard operator&(Bitboard b, Square s) {
   return b & SquareBB[s];
 }
 
-inline Bitboard& operator|=(Bitboard& b, Square s) {
-  return b |= SquareBB[s];
-}
-
-inline Bitboard& operator^=(Bitboard& b, Square s) {
-  return b ^= SquareBB[s];
-}
-
 inline Bitboard operator|(Bitboard b, Square s) {
   return b | SquareBB[s];
 }
@@ -108,32 +101,21 @@ inline Bitboard operator^(Bitboard b, Square s) {
   return b ^ SquareBB[s];
 }
 
+inline Bitboard& operator|=(Bitboard& b, Square s) {
+  return b |= SquareBB[s];
+}
+
+inline Bitboard& operator^=(Bitboard& b, Square s) {
+  return b ^= SquareBB[s];
+}
+
 inline bool more_than_one(Bitboard b) {
   return b & (b - 1);
 }
 
-template<typename T> inline int distance(T x, T y) { return x < y ? y - x : x - y; }
-template<> inline int distance<Square>(Square x, Square y) { return SquareDistance[x][y]; }
 
-template<typename T1, typename T2> inline int distance(T2 x, T2 y);
+/// rank_bb() and file_bb() return a bitboard representing all the squares on
-template<> inline int distance<File>(Square x, Square y) { return distance(file_of(x), file_of(y)); }
+/// the given file or rank.
-template<> inline int distance<Rank>(Square x, Square y) { return distance(rank_of(x), rank_of(y)); }
-
-
-/// shift_bb() moves bitboard one step along direction Delta. Mainly for pawns.
-
-template<Square Delta>
-inline Bitboard shift_bb(Bitboard b) {
-
-  return  Delta == DELTA_N  ?  b             << 8 : Delta == DELTA_S  ?  b             >> 8
-        : Delta == DELTA_NE ? (b & ~FileHBB) << 9 : Delta == DELTA_SE ? (b & ~FileHBB) >> 7
-        : Delta == DELTA_NW ? (b & ~FileABB) << 7 : Delta == DELTA_SW ? (b & ~FileABB) >> 9
-        : 0;
-}
-
-
-/// rank_bb() and file_bb() take a file or a square as input and return
-/// a bitboard representing all squares on the given file or rank.
 
 inline Bitboard rank_bb(Rank r) {
   return RankBB[r];
@@ -152,83 +134,102 @@ inline Bitboard file_bb(Square s) {
 }
 
 
-/// adjacent_files_bb() takes a file as input and returns a bitboard representing
+/// shift_bb() moves a bitboard one step along direction Delta. Mainly for pawns
-/// all squares on the adjacent files.
+
+template<Square Delta>
+inline Bitboard shift_bb(Bitboard b) {
+  return  Delta == DELTA_N  ?  b             << 8 : Delta == DELTA_S  ?  b             >> 8
+        : Delta == DELTA_NE ? (b & ~FileHBB) << 9 : Delta == DELTA_SE ? (b & ~FileHBB) >> 7
+        : Delta == DELTA_NW ? (b & ~FileABB) << 7 : Delta == DELTA_SW ? (b & ~FileABB) >> 9
+        : 0;
+}
+
+
+/// adjacent_files_bb() returns a bitboard representing all the squares on the
+/// adjacent files of the given one.
 
 inline Bitboard adjacent_files_bb(File f) {
   return AdjacentFilesBB[f];
 }
 
 
-/// in_front_bb() takes a color and a rank as input, and returns a bitboard
+/// between_bb() returns a bitboard representing all the squares between the two
-/// representing all the squares on all ranks in front of the rank, from the
+/// given ones. For instance, between_bb(SQ_C4, SQ_F7) returns a bitboard with
-/// given color's point of view. For instance, in_front_bb(BLACK, RANK_3) will
+/// the bits for square d5 and e6 set. If s1 and s2 are not on the same rank, file
-/// give all squares on ranks 1 and 2.
+/// or diagonal, 0 is returned.
-
-inline Bitboard in_front_bb(Color c, Rank r) {
-  return InFrontBB[c][r];
-}
-
-
-/// between_bb() returns a bitboard representing all squares between two squares.
-/// For instance, between_bb(SQ_C4, SQ_F7) returns a bitboard with the bits for
-/// square d5 and e6 set.  If s1 and s2 are not on the same rank, file or diagonal,
-/// 0 is returned.
 
 inline Bitboard between_bb(Square s1, Square s2) {
   return BetweenBB[s1][s2];
 }
 
 
-/// forward_bb() takes a color and a square as input, and returns a bitboard
+/// in_front_bb() returns a bitboard representing all the squares on all the ranks
-/// representing all squares along the line in front of the square, from the
+/// in front of the given one, from the point of view of the given color. For
-/// point of view of the given color. Definition of the table is:
+/// instance, in_front_bb(BLACK, RANK_3) will return the squares on ranks 1 and 2.
-/// ForwardBB[c][s] = in_front_bb(c, s) & file_bb(s)
+
+inline Bitboard in_front_bb(Color c, Rank r) {
+  return InFrontBB[c][r];
+}
+
+
+/// forward_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, s) & file_bb(s)
 
 inline Bitboard forward_bb(Color c, Square s) {
   return ForwardBB[c][s];
 }
 
 
-/// pawn_attack_span() takes a color and a square as input, and returns a bitboard
+/// pawn_attack_span() returns a bitboard representing all the squares that can be
-/// representing all squares that can be attacked by a pawn of the given color
+/// attacked by a pawn of the given color when it moves along its file, starting
-/// when it moves along its file starting from the given square. Definition is:
+/// from the given square:
-/// PawnAttackSpan[c][s] = in_front_bb(c, s) & adjacent_files_bb(s);
+///       PawnAttackSpan[c][s] = in_front_bb(c, s) & adjacent_files_bb(s);
 
 inline Bitboard pawn_attack_span(Color c, Square s) {
   return PawnAttackSpan[c][s];
 }
 
 
-/// passed_pawn_mask() takes a color and a square as input, and returns a
+/// passed_pawn_mask() returns a bitboard mask which can be used to test if a
-/// bitboard mask which can be used to test if a pawn of the given color on
+/// pawn of the given color and on the given square is a passed pawn:
-/// the given square is a passed pawn. Definition of the table is:
+///       PassedPawnMask[c][s] = pawn_attack_span(c, s) | forward_bb(c, s)
-/// PassedPawnMask[c][s] = pawn_attack_span(c, s) | forward_bb(c, s)
 
 inline Bitboard passed_pawn_mask(Color c, Square s) {
   return PassedPawnMask[c][s];
 }
 
 
-/// squares_of_color() returns a bitboard representing all squares with the same
+/// squares_of_color() returns a bitboard representing all the squares of the
-/// color of the given square.
+/// same color of the given one.
 
 inline Bitboard squares_of_color(Square s) {
   return DarkSquares & s ? DarkSquares : ~DarkSquares;
 }
 
 
-/// aligned() returns true if the squares s1, s2 and s3 are aligned
+/// aligned() returns true if the squares s1, s2 and s3 are aligned either on a
-/// either on a straight or on a diagonal line.
+/// straight or on a diagonal line.
 
 inline bool aligned(Square s1, Square s2, Square s3) {
   return LineBB[s1][s2] & s3;
 }
 
 
-/// Functions for computing sliding attack bitboards. Function attacks_bb() takes
+/// distance() functions return the distance between x and y, defined as the
-/// a square and a bitboard of occupied squares as input, and returns a bitboard
+/// number of steps for a king in x to reach y. Works with squares, ranks, files.
-/// representing all squares attacked by Pt (bishop or rook) on the given square.
+
+template<typename T> inline int distance(T x, T y) { return x < y ? y - x : x - y; }
+template<> inline int distance<Square>(Square x, Square y) { return SquareDistance[x][y]; }
+
+template<typename T1, typename T2> inline int distance(T2 x, T2 y);
+template<> inline int distance<File>(Square x, Square y) { return distance(file_of(x), file_of(y)); }
+template<> inline int distance<Rank>(Square x, Square y) { return distance(rank_of(x), rank_of(y)); }
+
+
+/// attacks_bb() returns a bitboard representing all the squares attacked by a
+/// piece of type Pt (bishop or rook) placed on 's'. The helper magic_index()
+/// looks up the index using the 'magic bitboards' approach.
 template<PieceType Pt>
 FORCE_INLINE unsigned magic_index(Square s, Bitboard occupied) {
 
@@ -263,8 +264,8 @@ inline Bitboard attacks_bb(Piece pc, Square s, Bitboard occupied) {
   }
 }
 
-/// lsb()/msb() finds the least/most significant bit in a non-zero bitboard.
+
-/// pop_lsb() finds and clears the least significant bit in a non-zero bitboard.
+/// lsb() and msb() return the least/most significant bit in a non-zero bitboard
 
 #ifdef USE_BSFQ
 
@@ -297,7 +298,7 @@ FORCE_INLINE Square lsb(Bitboard b) {
   return (Square) (uint32_t(b) ? lsb32(uint32_t(b)) : 32 + lsb32(uint32_t(b >> 32)));
 }
 
-#  else
+#  else // Assumed gcc or compatible compiler
 
 FORCE_INLINE Square lsb(Bitboard b) { // Assembly code by Heinz van Saanen
   Bitboard idx;
@@ -313,21 +314,24 @@ FORCE_INLINE Square msb(Bitboard b) {
 
 #  endif
 
+#else // ifdef(USE_BSFQ)
+
+Square lsb(Bitboard b);
+Square msb(Bitboard b);
+
+#endif
+
+
+/// pop_lsb() finds and clears the least significant bit in a non-zero bitboard
+
 FORCE_INLINE Square pop_lsb(Bitboard* b) {
   const Square s = lsb(*b);
   *b &= *b - 1;
   return s;
 }
 
-#else // if defined(USE_BSFQ)
 
-extern Square msb(Bitboard b);
+/// frontmost_sq() and backmost_sq() return the square corresponding to the
-extern Square lsb(Bitboard b);
-extern Square pop_lsb(Bitboard* b);
-
-#endif
-
-/// frontmost_sq() and backmost_sq() find the square corresponding to the
 /// most/least advanced bit relative to the given color.
 
 inline Square frontmost_sq(Color c, Bitboard b) { return c == WHITE ? msb(b) : lsb(b); }

src/endgame.cpp

@@ -217,7 +217,7 @@ Value Endgame<KPK>::operator()(const Position& pos) const {
 
   Color us = strongSide == pos.side_to_move() ? WHITE : BLACK;
 
-  if (!Bitbases::probe_kpk(wksq, psq, bksq, us))
+  if (!Bitbases::probe(wksq, psq, bksq, us))
       return VALUE_DRAW;
 
   Value result = VALUE_KNOWN_WIN + PawnValueEg + Value(rank_of(psq));
@@ -852,5 +852,5 @@ ScaleFactor Endgame<KPKP>::operator()(const Position& pos) const {
 
   // Probe the KPK bitbase with the weakest side's pawn removed. If it's a draw,
   // it's probably at least a draw even with the pawn.
-  return Bitbases::probe_kpk(wksq, psq, bksq, us) ? SCALE_FACTOR_NONE : SCALE_FACTOR_DRAW;
+  return Bitbases::probe(wksq, psq, bksq, us) ? SCALE_FACTOR_NONE : SCALE_FACTOR_DRAW;
 }

src/main.cpp

@@ -35,7 +35,7 @@ int main(int argc, char* argv[]) {
   UCI::init(Options);
   Bitboards::init();
   Position::init();
-  Bitbases::init_kpk();
+  Bitbases::init();
   Search::init();
   Eval::init();
   Pawns::init();

src/pawns.cpp

@@ -288,7 +288,7 @@ Score Entry::do_king_safety(const Position& pos, Square ksq) {
 
   Bitboard pawns = pos.pieces(Us, PAWN);
   if (pawns)
-      while (!(DistanceRingsBB[ksq][minKingPawnDistance[Us]++] & pawns)) {}
+      while (!(DistanceRingBB[ksq][minKingPawnDistance[Us]++] & pawns)) {}
 
   if (relative_rank(Us, ksq) > RANK_4)
       return make_score(0, -16 * minKingPawnDistance[Us]);