Rewrite pop_1st_bit() to be endian independent

[stockfish] / src / bitboard.cpp

diff --git a/src/bitboard.cpp b/src/bitboard.cpp
index ebd048be8474800eb6507a5dfb64bfacc18061eb..40cdbb21ff956601238b0db0dc72176e5cb081cb 100644 (file)
--- a/src/bitboard.cpp
+++ b/src/bitboard.cpp
@@ -68,24 +68,6 @@ namespace {
                    Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
 }
 
-
-/// print_bitboard() prints a bitboard in an easily readable format to the
-/// standard output. This is sometimes useful for debugging.
-
-void print_bitboard(Bitboard b) {
-
-  for (Rank r = RANK_8; r >= RANK_1; r--)
-  {
-      std::cout << "+---+---+---+---+---+---+---+---+" << '\n';
-      for (File f = FILE_A; f <= FILE_H; f++)
-          std::cout << "| " << ((b & make_square(f, r)) ? "X " : "  ");
-
-      std::cout << "|\n";
-  }
-  std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
-}
-
-
 /// first_1() finds the least significant nonzero bit in a nonzero bitboard.
 /// pop_1st_bit() finds and clears the least significant nonzero bit in a
 /// nonzero bitboard.
@@ -110,62 +92,72 @@ Square first_1(Bitboard b) {
   return Square(BSFTable[(fold * 0x783A9B23) >> 26]);
 }
 
-// Use type-punning
-union b_union {
-
-    Bitboard dummy;
-    struct {
-#if defined (BIGENDIAN)
-        uint32_t h;
-        uint32_t l;
-#else
-        uint32_t l;
-        uint32_t h;
-#endif
-    } b;
-};
-
 Square pop_1st_bit(Bitboard* b) {
 
-   const b_union u = *((b_union*)b);
-
-   if (u.b.l)
-   {
-       ((b_union*)b)->b.l = u.b.l & (u.b.l - 1);
-       return Square(BSFTable[((u.b.l ^ (u.b.l - 1)) * 0x783A9B23) >> 26]);
-   }
-
-   ((b_union*)b)->b.h = u.b.h & (u.b.h - 1);
-   return Square(BSFTable[((~(u.b.h ^ (u.b.h - 1))) * 0x783A9B23) >> 26]);
+  Bitboard bb = *b;
+  *b = bb & (bb - 1);
+  bb ^= (bb - 1);
+  uint32_t fold = unsigned(bb) ^ unsigned(bb >> 32);
+  return Square(BSFTable[(fold * 0x783A9B23) >> 26]);
 }
 
-#endif // !defined(USE_BSFQ)
-
-#if !defined(USE_BSFQ)
-
 Square last_1(Bitboard b) {
+
+  unsigned b32;
   int result = 0;
-  if (b > 0xFFFFFFFF) {
-    b >>= 32;
-    result = 32;
+
+  if (b > 0xFFFFFFFF)
+  {
+      b >>= 32;
+      result = 32;
   }
-  if (b > 0xFFFF) {
-    b >>= 16;
-    result += 16;
+
+  b32 = unsigned(b);
+
+  if (b32 > 0xFFFF)
+  {
+      b32 >>= 16;
+      result += 16;
   }
-  if (b > 0xFF) {
-    b >>= 8;
-    result += 8;
+
+  if (b32 > 0xFF)
+  {
+      b32 >>= 8;
+      result += 8;
   }
-  return Square(result + MS1BTable[b]);
+
+  return Square(result + MS1BTable[b32]);
 }
 
 #endif // !defined(USE_BSFQ)
 
-/// bitboards_init() initializes various bitboard arrays. It is called during
+
+/// Bitboards::print() prints a bitboard in an easily readable format to the
+/// standard output. This is sometimes useful for debugging.
+
+void Bitboards::print(Bitboard b) {
+
+  for (Rank rank = RANK_8; rank >= RANK_1; rank--)
+  {
+      std::cout << "+---+---+---+---+---+---+---+---+" << '\n';
+
+      for (File file = FILE_A; file <= FILE_H; file++)
+          std::cout << "| " << ((b & make_square(file, rank)) ? "X " : "  ");
+
+      std::cout << "|\n";
+  }
+  std::cout << "+---+---+---+---+---+---+---+---+" << std::endl;
+}
+
+
+/// Bitboards::init() initializes various bitboard arrays. It is called during
 /// program initialization.
 
-void bitboards_init() {
+void Bitboards::init() {
+
+  for (int k = 0, i = 0; i < 8; i++)
+      while (k < (2 << i))
+          MS1BTable[k++] = i;
 
   for (Bitboard b = 0; b < 256; b++)
       BitCount8Bit[b] = (uint8_t)popcount<Max15>(b);
@@ -217,11 +209,6 @@ void bitboards_init() {
       else
           BSFTable[((1ULL << i) * 0x218A392CD3D5DBFULL) >> 58] = i;
 
-  MS1BTable[0] = 0;
-  for (int i = 0, k = 1; i < 8; i++)
-    for (int j = 0; j < (1 << i); j++)
-      MS1BTable[k++] = i;
-
   int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
                      {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
 
@@ -232,7 +219,7 @@ void bitboards_init() {
               {
                   Square to = s + Square(c == WHITE ? steps[pt][k] : -steps[pt][k]);
 
-                  if (square_is_ok(to) && square_distance(s, to) < 3)
+                  if (is_ok(to) && square_distance(s, to) < 3)
                       StepAttacksBB[make_piece(c, pt)][s] |= to;
               }
 
@@ -269,7 +256,7 @@ namespace {
 
     for (int i = 0; i < 4; i++)
         for (Square s = sq + deltas[i];
-             square_is_ok(s) && square_distance(s, s - deltas[i]) == 1;
+             is_ok(s) && square_distance(s, s - deltas[i]) == 1;
              s += deltas[i])
         {
             attack |= s;