Split platform specific time measurement away

We now have a `stopwatch` to measure time between two moments.

src/platform.h

@@ -8,6 +8,8 @@
 
 #include "compiler_specifics.h"
 
+#include <stdint.h>
+
 /* Error Reporting */
 
 /* BSD errx function, seen in err.h */
@@ -15,4 +17,39 @@ H_MSVC_DECLSPEC(noreturn) \
 void h_platform_errx(int err, const char* format, ...)	\
   H_GCC_ATTRIBUTE((noreturn, format (printf,2,3)));
 
+/* Time Measurement */
+
+struct HStopWatch; /* forward definition */
+
+/* initialize a stopwatch */
+void h_platform_stopwatch_reset(struct HStopWatch* stopwatch);
+
+/* return difference between last reset point and now */
+int64_t h_platform_stopwatch_ns(struct HStopWatch* stopwatch);
+
+/* Platform dependent definitions for HStopWatch */
+#if defined(_MSC_VER)
+
+#ifndef WIN32_LEAN_AND_MEAN
+#define WIN32_LEAN_AND_MEAN 1
+#endif
+#include <windows.h>
+#undef WIN32_LEAN_AND_MEAN
+
+struct HStopWatch {
+  LARGE_INTEGER qpf;
+  LARGE_INTEGER start;
+};
+
+#else
+/* Unix like platforms */
+
+#include <time.h>
+
+struct HStopWatch {
+  struct timespec start;
+};
+
+#endif
+
 #endif