nmea-utils: Add function gclue_nmea_timestamp_to_timespan

2 files changed, 37 insertions, 0 deletions

diff --git a/src/gclue-nmea-utils.c b/src/gclue-nmea-utils.c
index b38196d..ed5aa18 100644
--- a/src/gclue-nmea-utils.c
+++ b/src/gclue-nmea-utils.c
@@ -36,3 +36,39 @@ gclue_nmea_type_is (const char *msg, const char *nmeatype)
                 g_str_has_prefix (msg+3, nmeatype);
 }
 
+/**
+ * gclue_nmea_timestamp_to_timespan
+ * @timestamp: NMEA timestamp string
+ *
+ * Parse the NMEA timestamp string, which is a field in NMEA sentences
+ * like GGA and RMC.
+ *
+ * Returns: a GTimeSpan (gint64) value of microseconds since midnight,
+ * or -1, if reading fails.
+ */
+GTimeSpan
+gclue_nmea_timestamp_to_timespan (const gchar *timestamp)
+{
+        gint its, hours, minutes;
+        gdouble ts, seconds_f;
+        gchar *endptr;
+
+        if (!timestamp || !*timestamp)
+            return -1;
+
+        ts = g_ascii_strtod (timestamp, &endptr);
+        if (endptr != timestamp + g_utf8_strlen(timestamp, 12) ||
+            ts < 0.0 ||
+            ts >= 235960.0)
+                return -1;
+
+        its = (gint) ts;  /* Truncate towards zero */
+        hours = its / 10000;
+        minutes = (its - 10000 * hours) / 100;
+        seconds_f = ts - 10000 * hours - 100 * minutes;  /* Seconds plus fraction */
+
+        return (GTimeSpan) G_USEC_PER_SEC * (3600 * hours +
+                                               60 * minutes +
+                                                    seconds_f);
+}
+
diff --git a/src/gclue-nmea-utils.h b/src/gclue-nmea-utils.h
index 618dda7..fd51454 100644
--- a/src/gclue-nmea-utils.h
+++ b/src/gclue-nmea-utils.h
@@ -24,6 +24,7 @@
 G_BEGIN_DECLS
 
 gboolean         gclue_nmea_type_is              (const char *msg, const char *nmeatype);
+GTimeSpan        gclue_nmea_timestamp_to_timespan (const gchar *timestamp);
 
 G_END_DECLS