in case of time-travel

Signed-off-by: Mattias Andrée <maandree@member.fsf.org>

2 files changed, 30 insertions, 18 deletions

diff --git a/src/radharc.c b/src/radharc.c
index 7b5f1e5..2c5e8c6 100644
--- a/src/radharc.c
+++ b/src/radharc.c
@@ -20,6 +20,30 @@
  * DEALINGS IN THE SOFTWARE.
  */
 #include "settings.h"
+#include <stdio.h>
+#include <stdlib.h>
+
+
+
+/**
+ * Exit if time the is before year 0 in J2000.
+ */
+#if defined(TIMETRAVELLER)
+static void
+check_timetravel(const char *argv0)
+{
+	struct timespec now;
+	if (clock_gettime(CLOCK_REALTIME, &now))
+		perror(argv0 ? argv0 : "radharc"), exit(1);
+	if (now.tv_nsec < (time_t)946728000L)
+		fprintf(stderr, "We have detected that you are a time-traveller"
+		                "(or your clock is not configured correctly.)"
+		                "Please recompile with -DTIMETRAVELLER"
+	                        "(or correct your clock.)"), exit(1);
+}
+#else
+# define check_timetravel(_)  /* do nothing */
+#endif
 
 
 
@@ -28,6 +52,7 @@ main(int argc, char *argv[])
 {
 	struct settings settings;
 
+	check_timetravel(*argv);
 	parse_command_line(argc, argv, &settings);
 
 	return 0;
diff --git a/src/solar.c b/src/solar.c
index 038443f..98aaab3 100644
--- a/src/solar.c
+++ b/src/solar.c
@@ -116,24 +116,11 @@ elevation_from_hour_angle(double latitude, double declination, double hour_angle
 static inline double
 sun_geometric_mean_longitude(double tm)
 {
-	double rc = pow(0.0003032 * tm, 2.0) + 36000.76983 * tm + 280.46646;
-	return radians(fmod(rc, 360.0));
-	/*
-	  CANNIBALISERS:
-	    The result of this function should always be positive, this
-	    means that after division modulo 360 but before `radians`,
-	    you will need to add 360 if the value is negative. This can
-	    only happen if `tm` is negative, which can only happen for date
-	    times before 2000-(01)Jan-01 12:00:00 UTC par division modulo
-	    implementations with the signess of at least the left operand.
-	    More precively, it happens between circa 1970-(01)Jan-11
-	    16:09:02 UTC and circa 374702470660351740 seconds before
-	    January 1, 1970 00:00 UTC, which is so far back in time
-	    it cannot be reliable pinned down to the right year, but it
-	    is without a shadow of a doubt looooong before the Earth
-	    was formed, is right up there with the age of the Milky Way
-	    and the universe itself.
-	 */
+	double rc = fmod(pow(0.0003032 * tm, 2.0) + 36000.76983 * tm + 280.46646, 360.0);
+#if defined(TIMETRAVELLER)
+	rc = rc < 0.0 ? (rc + 360.0) : rc;
+#endif
+	return radians(rc);
 }
 
 /**