Simplify popcnt

[stockfish] / src / bitboard.h

diff --git a/src/bitboard.h b/src/bitboard.h
index 77a824ba62106965ba9513803a19c650c092bb4c..21dc6e44087a36e5c527d0d9a15b78119aa48463 100644 (file)
--- a/src/bitboard.h
+++ b/src/bitboard.h
@@ -257,6 +257,32 @@ inline Bitboard attacks_bb(Piece pc, Square s, Bitboard occupied) {
 }
 
 
+/// popcount() counts the number of non-zero bits in a bitboard
+
+inline int popcount(Bitboard b) {
+
+#ifndef USE_POPCNT
+
+  extern uint8_t PopCnt16[1 << 16];
+  union { Bitboard bb; uint16_t u[4]; } v = { b };
+  return PopCnt16[v.u[0]] + PopCnt16[v.u[1]] + PopCnt16[v.u[2]] + PopCnt16[v.u[3]];
+
+#elif defined(_MSC_VER) && defined(__INTEL_COMPILER)
+
+  return _mm_popcnt_u64(b);
+
+#elif defined(_MSC_VER)
+
+  return (int)__popcnt64(b);
+
+#else // Assumed gcc or compatible compiler
+
+  return __builtin_popcountll(b);
+
+#endif
+}
+
+
 /// lsb() and msb() return the least/most significant bit in a non-zero bitboard
 
 #if defined(__GNUC__)