Rewrite pop_1st_bit() to be endian independent

[stockfish] / src / bitboard.cpp

diff --git a/src/bitboard.cpp b/src/bitboard.cpp
index 6a3c18204667b4c0b8c010592ea9fe26a2e333e6..40cdbb21ff956601238b0db0dc72176e5cb081cb 100644 (file)
--- a/src/bitboard.cpp
+++ b/src/bitboard.cpp
@@ -92,37 +92,18 @@ 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]);
 }
 
 Square last_1(Bitboard b) {
 
+  unsigned b32;
   int result = 0;
 
   if (b > 0xFFFFFFFF)
@@ -131,19 +112,21 @@ Square last_1(Bitboard b) {
       result = 32;
   }
 
-  if (b > 0xFFFF)
+  b32 = unsigned(b);
+
+  if (b32 > 0xFFFF)
   {
-      b >>= 16;
+      b32 >>= 16;
       result += 16;
   }
 
-  if (b > 0xFF)
+  if (b32 > 0xFF)
   {
-      b >>= 8;
+      b32 >>= 8;
       result += 8;
   }
 
-  return Square(result + MS1BTable[b]);
+  return Square(result + MS1BTable[b32]);
 }
 
 #endif // !defined(USE_BSFQ)
@@ -236,7 +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;
               }
 
@@ -273,7 +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;