#else
asm("bsr %1, %0;" : "=r"(n) : "r"(x));
#endif
+
#elif defined(FACTOR_AMD64)
#if defined(_MSC_VER)
n = 0;
#else
asm("bsr %1, %0;" : "=r"(n) : "r"(x));
#endif
-#elif defined(FACTOR_PPC64)
-#if defined(__GNUC__)
- n = (63 - __builtin_clzll(x));
+
+#elif defined(FACTOR_ARM)
+#if defined(_MSC_VER)
+ _BitScanReverse((unsigned long*)&n, x);
#else
-#error Unsupported compiler
+ n = (31 - __builtin_clz(x));
#endif
+
+#elif defined(FACTOR_ARM64)
+#if defined(_MSC_VER)
+ n = 0;
+ _BitScanReverse64((unsigned long*)&n, x);
+#else
+ n = (63 - __builtin_clzll(x));
+#endif
+
#elif defined(FACTOR_PPC32)
#if defined(__GNUC__)
n = (31 - __builtin_clz(x));
#else
#error Unsupported compiler
#endif
+
+#elif defined(FACTOR_PPC64)
+#if defined(__GNUC__)
+ n = (63 - __builtin_clzll(x));
+#else
+#error Unsupported compiler
+#endif
+
#else
#error Unsupported CPU
#endif