(timeval_diff_d): New function.

src/libraries/libmisc/timeval-util.c

@@ -144,6 +144,12 @@ timeval_diff_sec(struct timeval a, struct timeval b)
     return res.tv_sec + (res.tv_usec >= 500000);
 }
 
+double
+timeval_diff_d(struct timeval a, struct timeval b)
+{
+    return (a.tv_sec - b.tv_sec) + 1e-6 * (a.tv_usec - b.tv_usec);
+}
+
 int
 setup_timer(struct timeval *tv,
 	    struct timeval interval)

src/libraries/libmisc/timeval-util.h

@@ -42,6 +42,9 @@ extern Bool timeval_less(struct timeval a, struct timeval b);
 /* Return the difference as a number of seconds, properly rounded. */
 extern long timeval_diff_sec(struct timeval a, struct timeval b);
 
+/* Return the difference as a number of seconds, as a double. */
+extern double timeval_diff_d(struct timeval a, struct timeval b);
+
 /* Set TV to the current time plus INTERVAL.  Return -1 if
    gettimeofday() fails (check errno).  */
 extern int setup_timer(struct timeval *tv, struct timeval interval);