gpsutil.c: fill_dop bug if sats < 4

bug present where it would try to invert matrix with out enough data...
added guard to prevent trying to calculate dop's if we don't have 4 sats
with current code.

1 files changed, 12 insertions, 0 deletions

diff --git a/gpsutils.c b/gpsutils.c
index 6b94de0e..1bf200ed 100644
--- a/gpsutils.c
+++ b/gpsutils.c
@@ -466,6 +466,8 @@ gps_mask_t fill_dop(const struct gps_data_t * gpsdata, struct dop_t * dop)
     double xdop, ydop, hdop, vdop, pdop, tdop, gdop;
     int i, j, k, n;
 
+    memset(satpos, 0, sizeof(satpos));
+
 #ifdef __UNUSED__
     gpsd_report(LOG_INF, "Satellite picture:\n");
     for (k = 0; k < MAXCHANNELS; k++) {
@@ -488,6 +490,16 @@ gps_mask_t fill_dop(const struct gps_data_t * gpsdata, struct dop_t * dop)
 	n++;
     }
 
+    /* If we don't have 4 satellites then we don't have enough information to calculate DOPS */
+    if (n < 4) {
+	gpsd_report(LOG_DATA + 2, "Not enough Satellites available %d < 4:\n",
+		    n);
+	return 0;		/* Is this correct return code here? or should it be ERROR_IS */
+    }
+
+    memset(prod, 0, sizeof(prod));
+    memset(inv, 0, sizeof(inv));
+
 #ifdef __UNUSED__
     gpsd_report(LOG_INF, "Line-of-sight matrix:\n");
     for (k = 0; k < n; k++) {