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>
diff --git a/tests/timespec-test.c b/tests/timespec-test.c
index cd3b1c1..712d1ac 100644
--- a/tests/timespec-test.c
+++ b/tests/timespec-test.c
@@ -60,6 +60,15 @@
 	ZUC_ASSERT_EQ(timespec_to_nsec(&a), (NSEC_PER_SEC * 4ULL) + 4);
 }
 
+ZUC_TEST(timespec_test, timespec_to_msec)
+{
+	struct timespec a;
+
+	a.tv_sec = 4;
+	a.tv_nsec = 4000000;
+	ZUC_ASSERT_EQ(timespec_to_msec(&a), (4000ULL) + 4);
+}
+
 ZUC_TEST(timespec_test, millihz_to_nsec)
 {
 	ZUC_ASSERT_EQ(millihz_to_nsec(60000), 16666666);