shared: Add timespec_to_proto helper function

Add helper function to convert from struct timespec values to tv_sec_hi,
tv_sec_lo, tv_nsec triplets used for sending high-resolution timestamp
data over the wayland protocol. Replace existing conversion code with
the helper function.

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

shared/timespec-util.h

@@ -147,6 +147,30 @@ timespec_to_usec(const struct timespec *a)
 	return (int64_t)a->tv_sec * 1000000 + a->tv_nsec / 1000;
 }
 
+/* Convert timespec to protocol data
+ *
+ * \param a timespec
+ * \param tv_sec_hi[out] the high bytes of the seconds part
+ * \param tv_sec_lo[out] the low bytes of the seconds part
+ * \param tv_nsec[out] the nanoseconds part
+ *
+ * The input timespec must be normalized (the nanoseconds part should
+ * be less than 1 second) and non-negative.
+ */
+static inline void
+timespec_to_proto(const struct timespec *a, uint32_t *tv_sec_hi,
+                  uint32_t *tv_sec_lo, uint32_t *tv_nsec)
+{
+	assert(a->tv_sec >= 0);
+	assert(a->tv_nsec >= 0 && a->tv_nsec < NSEC_PER_SEC);
+
+	uint64_t sec64 = a->tv_sec;
+
+	*tv_sec_hi = sec64 >> 32;
+	*tv_sec_lo = sec64 & 0xffffffff;
+	*tv_nsec = a->tv_nsec;
+}
+
 /* Convert nanoseconds to timespec
  *
  * \param a timespec