Fix sign of PPS offset in gpsmon.

In gpsmon client mode the u-blox now exactly matches what
I see in ntpq -p.

1 files changed, 11 insertions, 5 deletions

diff --git a/monitor_sirf.c b/monitor_sirf.c
index ba8bb9f2..6ef24c19 100644
--- a/monitor_sirf.c
+++ b/monitor_sirf.c
@@ -9,6 +9,7 @@
 #include <stdbool.h>
 #include <string.h>
 #include <math.h>
+#include <stdlib.h> /* for labs() */
 #include <assert.h>
 #include <time.h>
 #include <sys/time.h>
@@ -592,15 +593,20 @@ static void sirf_update(void)
     if (pps_thread_lastpps(&session, &drift) > 0) {
 	/* NOTE: can not use double here due to precision requirements */
 	struct timespec timedelta;
-	TS_SUB( &timedelta, &drift.real, &drift.clock);
-        if ( 86400 < (long)timedelta.tv_sec ) {
+        int sign = ' ';
+	TS_SUB( &timedelta, &drift.clock, &drift.real);
+        if ( 86400 < (long)labs(timedelta.tv_sec) ) {
 	    /* more than one day off, overflow */
             /* need a bigger field to show it */
 	    (void)mvwprintw(mid7win, 2, 39, "> 1 day");
         } else {
-	    (void)mvwprintw(mid7win, 4, 39, "%ld.%09ld",
-				  (long)timedelta.tv_sec,
-				  (long)timedelta.tv_nsec);
+	    if ( 0 > timedelta.tv_nsec ) {
+		sign = '-';
+	    }
+	    (void)mvwprintw(mid7win, 4, 39, "%c%ld.%09ld",
+				  sign,
+			          (long)timedelta.tv_sec,
+				  (long)labs(timedelta.tv_nsec));
         }
 	(void)wnoutrefresh(mid7win);
     }