Add lj_num2u64 for number to uint64_t conversion.

src/lj_obj.h

@@ -763,6 +763,17 @@ static LJ_AINLINE int32_t lj_num2bit(lua_Number n)
 #define lj_num2int(n)   ((int32_t)(n))
 #endif
 
+static LJ_AINLINE uint64_t lj_num2u64(lua_Number n)
+{
+#ifdef _MSC_VER
+  if (n >= 9223372036854775808.0)  /* They think it's a feature. */
+    return (uint64_t)(int64_t)(n - 9223372036854775808.0) +
+	   U64x(80000000,00000000);
+  else
+#endif
+    return (uint64_t)n;
+}
+
 /* -- Miscellaneous object handling --------------------------------------- */
 
 /* Names and maps for internal and external object tags. */