time: Timer -> StopWatch; time.Duration

vlib/time/time_windows.c.v

@@ -12,8 +12,48 @@ struct C.tm {
 	tm_sec  int
 }
 
+[typedef]
+struct C.LARGE_INTEGER {
+	QuadPart i64
+}
+
+const (
+	// start_time is needed on Darwin and Windows because of potential overflows
+	// Windows: don't store the LARGE_INTEGER, just the QuadPart
+	start_time = init_win_time_start()
+	freq_time  = init_win_time_freq()
+)
+
 fn C._mkgmtime(&C.tm) time_t
 
+fn C.QueryPerformanceCounter(&C.LARGE_INTEGER) C.BOOL
+
+fn C.QueryPerformanceFrequency(&C.LARGE_INTEGER) C.BOOL
+
 fn make_unix_time(t C.tm) int {
 	return int(C._mkgmtime(&t))
 }
+
+fn init_win_time_freq() u64 {
+	mut f := C.LARGE_INTEGER{}
+	_ := C.QueryPerformanceFrequency(&f)
+	return u64(f.QuadPart)
+}
+
+fn init_win_time_start() u64 {
+	mut s := C.LARGE_INTEGER{}
+	_ := C.QueryPerformanceCounter(&s)
+	return u64(s.QuadPart)
+}
+
+fn sys_mono_now() u64 {
+	mut tm := C.LARGE_INTEGER{}
+	_ := C.QueryPerformanceCounter(&tm) // XP or later never fail
+	return mul_div(u64(tm.QuadPart) - start_time, 1_000_000_000, freq_time)
+}
+
+fn mul_div(val, numer, denom u64) u64 {
+	q := val / denom
+	r := val % denom
+	return q * numer + r * numer / denom
+}