Replace asserts with invalid value returning

Author: Pasi Miettinen

include/libswiftnav/time.h

@@ -77,13 +77,16 @@
 #define GPS_EPOCH 315964800
 
 #define WN_UNKNOWN -1
+#define TOW_UNKNOWN -1
 
 /** Structure representing a GPS time. */
 typedef struct __attribute__((packed)) {
   double tow; /**< Seconds since the GPS start of week. */
   s16 wn;     /**< GPS week number. */
 } gps_time_t;
 
+#define GPS_TIME_UNKNOWN ((gps_time_t){TOW_UNKNOWN, WN_UNKNOWN})
+
 void normalize_gps_time(gps_time_t *t_gps);
 
 time_t gps2time(const gps_time_t *t);

src/time.c

@@ -144,9 +144,10 @@ gps_time_t glo_time2gps_time(u16 nt, u8 n4, s8 h, s8 m, s8 s)
   u8 j = 0;
   u16 day_of_year = 0;
   u32 glo_year = 0;
-  gps_time_t gps_t = {0, 0};
+  gps_time_t gps_t = GPS_TIME_UNKNOWN;
 
-  assert(n4 >= N4_MIN && n4 <= N4_MAX);
+  if (n4 < N4_MIN || n4 > N4_MAX)
+    return GPS_TIME_UNKNOWN;
 
   if (nt >= GLO_NT_0_FLOOR && nt <= GLO_NT_0_CEILING) {
     j = 1;
@@ -165,7 +166,7 @@ gps_time_t glo_time2gps_time(u16 nt, u8 n4, s8 h, s8 m, s8 s)
     day_of_year = nt - LEAP_YEAR_DAYS - YEAR_DAYS * 2;
   }
   else
-    assert(0 && "invalid nt");
+    return GPS_TIME_UNKNOWN;
 
   glo_year = 1996 + 4 * (n4 - 1) + (j - 1);