timespec: Add timespec_to_msec helper

Paralleling timespec_to_nsec, converts to milliseconds.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
[Pekka: added doc about flooring]
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

shared/timespec-util.h

@@ -93,6 +93,19 @@ timespec_to_nsec(const struct timespec *a)
 	return (int64_t)a->tv_sec * NSEC_PER_SEC + a->tv_nsec;
 }
 
+/* Convert timespec to milliseconds
+ *
+ * \param a timespec
+ * \return milliseconds
+ *
+ * Rounding to integer milliseconds happens always down (floor()).
+ */
+static inline int64_t
+timespec_to_msec(const struct timespec *a)
+{
+	return (int64_t)a->tv_sec * 1000 + a->tv_nsec / 1000000;
+}
+
 /* Convert milli-Hertz to nanoseconds
  *
  * \param mhz frequency in mHz, not zero