add tutil_tvdiff_secs() for completeness

tests/libtest/testutil.c

@@ -98,6 +98,17 @@ long tutil_tvdiff(struct timeval newer, struct timeval older)
     (newer.tv_usec-older.tv_usec)/1000;
 }
 
+/*
+ * Same as tutil_tvdiff but with full usec resolution.
+ *
+ * Returns: the time difference in seconds with subsecond resolution.
+ */
+double tutil_tvdiff_secs(struct timeval newer, struct timeval older)
+{
+  return (double)(newer.tv_sec-older.tv_sec)+
+    (double)(newer.tv_usec-older.tv_usec)/1000000.0;
+}
+
 /* return the number of seconds in the given input timeval struct */
 long tutil_tvlong(struct timeval t1)
 {

tests/libtest/testutil.h

@@ -56,6 +56,13 @@ struct timeval tutil_tvnow(void);
  */
 long tutil_tvdiff(struct timeval t1, struct timeval t2);
 
+/*
+ * Same as tutil_tvdiff but with full usec resolution.
+ *
+ * Returns: the time difference in seconds with subsecond resolution.
+ */
+double tutil_tvdiff_secs(struct timeval t1, struct timeval t2);
+
 long tutil_tvlong(struct timeval t1);