Magic::index()

Make magic_index() a member of Magic since it uses all it's members
and keep us from having to pass the function pointer around to
init_magics().

No functional change

Closes official-stockfish#1146

src/bitboard.cpp

@@ -54,9 +54,7 @@ namespace {
   Bitboard RookTable[0x19000];  // To store rook attacks
   Bitboard BishopTable[0x1480]; // To store bishop attacks
 
-  typedef unsigned (Fn)(const Magic&, Bitboard);
-
-  void init_magics(Bitboard table[], Magic magics[], Square deltas[], Fn index);
+  void init_magics(Bitboard table[], Magic magics[], Square deltas[]);
 
   // 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.
@@ -204,8 +202,8 @@ void Bitboards::init() {
   Square RookDeltas[] = { NORTH,  EAST,  SOUTH,  WEST };
   Square BishopDeltas[] = { NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST };
 
-  init_magics(RookTable, RookMagics, RookDeltas, magic_index);
-  init_magics(BishopTable, BishopMagics, BishopDeltas, magic_index);
+  init_magics(RookTable, RookMagics, RookDeltas);
+  init_magics(BishopTable, BishopMagics, BishopDeltas);
 
   for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
   {
@@ -251,7 +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[], Fn index) {
+  void init_magics(Bitboard table[], Magic magics[], Square deltas[]) {
 
     int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998,  5731, 95205, 104912, 17020 },
                              {  728, 10316, 55013, 32803, 12281, 15100,  16645,   255 } };
@@ -311,7 +309,7 @@ namespace {
             // m.attacks[] after every failed attempt.
             for (++cnt, i = 0; i < size; ++i)
             {
-                unsigned idx = index(m, occupancy[i]);
+                unsigned idx = m.index(occupancy[i]);
 
                 if (epoch[idx] < cnt)
                 {

src/bitboard.h

@@ -82,6 +82,20 @@ struct Magic {
   Bitboard  magic;
   Bitboard* attacks;
   unsigned  shift;
+
+  /// looks up the index using the 'magic bitboards' approach.
+  unsigned index(Bitboard occupied) const {
+
+      if (HasPext)
+          return unsigned(pext(occupied, mask));
+
+      if (Is64Bit)
+          return unsigned(((occupied & mask) * magic) >> shift);
+
+      unsigned lo = unsigned(occupied) & unsigned(mask);
+      unsigned hi = unsigned(occupied >> 32) & unsigned(mask >> 32);
+      return (lo * unsigned(magic) ^ hi * unsigned(magic >> 32)) >> shift;
+  }
 };
 
 extern Magic RookMagics[SQUARE_NB];
@@ -222,26 +236,13 @@ template<> inline int distance<Rank>(Square x, Square y) { return distance(rank_
 
 
 /// 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.
-inline unsigned magic_index(const Magic& m, Bitboard occupied) {
-
-  if (HasPext)
-      return unsigned(pext(occupied, m.mask));
-
-  if (Is64Bit)
-      return unsigned(((occupied & m.mask) * m.magic) >> m.shift);
-
-  unsigned lo = unsigned(occupied) & unsigned(m.mask);
-  unsigned hi = unsigned(occupied >> 32) & unsigned(m.mask >> 32);
-  return (lo * unsigned(m.magic) ^ hi * unsigned(m.magic >> 32)) >> m.shift;
-}
+/// piece of type Pt (bishop or rook) placed on 's'.
 
 template<PieceType Pt>
 inline Bitboard attacks_bb(Square s, Bitboard occupied) {
 
   const Magic& M = Pt == ROOK ? RookMagics[s] : BishopMagics[s];
-  return M.attacks[magic_index(M, occupied)];
+  return M.attacks[M.index(occupied)];
 }
 
 inline Bitboard attacks_bb(PieceType pt, Square s, Bitboard occupied) {