$OpenBSD$
--- source/vdrift/numprocessors.h.orig	Mon Jul 15 02:49:53 2013
+++ source/vdrift/numprocessors.h	Mon Jul 15 02:55:54 2013
@@ -8,7 +8,7 @@ namespace NUMPROCESSORS
 	|| defined (_WIN64) || defined(__CYGWIN__) || defined(__MINGW32__)
 	#include <windows.h>
 	#include <process.h>
-#elif defined(__APPLE__) || defined (__FreeBSD__)
+#elif defined(__APPLE__) || defined (__FreeBSD__) || defined(__OpenBSD__)
 	//#include <pthread.h>
 
 	// Required to get number of processors on OS X using sysctlbyname.
@@ -43,6 +43,17 @@ namespace NUMPROCESSORS
 		{
 			return (unsigned int)numProcessors;
 		}
+#elif defined(__OpenBSD__)
+		int ncpu;
+		size_t size = sizeof(ncpu);
+		int mib[2];
+
+		mib[0] = CTL_HW;
+		mib[1] = HW_NCPU;
+		if (sysctl(mib, 2, &ncpu, &size, NULL, 0) == -1)
+			return 1;
+		else
+			return ncpu;
 #else
 		// Methods for getting the number of processors: