iAdd function get_cpu_count.

bench/common.h

@@ -30,3 +30,37 @@ static void test_function(const char str[], size_t n, void (*func)(size_t))
   end = (end - start) / 1000U;
   printf ("%s %Lu ms for n = %lu\n", str, end, n);
 }
+
+#if defined(_WIN32)
+# include <windows.h>
+#elif (defined(__APPLE__) && defined(__MACH__)) \
+  || defined(__DragonFly__) || defined(__FreeBSD__) \
+  || defined(__NetBSD__) || defined(__OpenBSD__)
+# include <sys/param.h>
+# include <sys/sysctl.h>
+# define USE_SYSCTL
+#else
+# include <unistd.h>
+#endif
+
+/* Return the number of CPU of the system */
+static inline int get_cpu_count(void)
+{
+#if defined(_WIN32)
+  SYSTEM_INFO sysinfo;
+  GetSystemInfo(&sysinfo);
+  return sysinfo.dwNumberOfProcessors;
+#elif defined(USE_SYSCTL)
+  int nm[2];
+  int count = 0;
+  size_t len = sizeof (count);
+  nm[0] = CTL_HW;
+  nm[1] = HW_NCPU;
+  sysctl(nm, 2, &count, &len, NULL, 0);
+  return MAX(1, count);
+#elif defined (_SC_NPROCESSORS_ONLN)
+  return sysconf(_SC_NPROCESSORS_ONLN);
+#else
+  return 1;
+#endif
+}