+/// 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
+}
+
+