Add calculations to switch between UTC and local time

src/calculations.c

@@ -13,17 +13,80 @@ float calc_rad_deg (float rad) {
   return 180/M_PI*rad;
 }
 
+int times_to_zone (int day_utc, int hour_utc, int day_local, int hour_local){
+  int time_zone;
+  if (day_utc == day_local){
+    time_zone = hour_local - hour_utc;
+  }
+  else{
+    if (abs(day_utc-day_local)>1){
+      if (day_utc < day_local){
+        day_local = day_utc-1;
+      }
+      else{
+        day_local = day_utc+1;
+      }
+    }
+    time_zone = 24*(day_local-day_utc)+(hour_local-hour_utc);
+  }
+  return time_zone;
+}
+
+void utc_zone_to_time (int *time_utc, int *time_local){
+  int sign = *(time_utc+6)/abs(*(time_utc+6));
+  *(time_local+3) = *(time_utc+3)+*(time_utc+6);
+  if (*(time_local+3)>24 || *(time_local+3) < 0){ /* Test if hours are still inside the same day */
+    *(time_local+3) = *(time_local+3)%24;
+    *(time_local+2) = *(time_utc+2)+sign;
+    if (*(time_local+2) > max_day_in_month (*(time_utc+1), *(time_utc)) || *(time_local+2) < 1){ /* Test if days are still inside the same month */
+      *(time_local+2) = (*(time_local+2)-1)%max_day_in_month (*(time_utc+1)+sign, *(time_utc))+1;
+      *(time_local+1) = *(time_utc+1)+sign;
+      if (*(time_local+1) > 12 || *(time_local+1) < 1){ /* Test if months are still inside the same year */
+        *(time_local+1) = (*(time_local+1)-1)%12+1;
+        *(time_local) = *(time_utc)+sign;
+      }
+    }
+  }
+}
+
+int max_day_in_month (int month, int year){
+  int max_days = 30;
+  /* check which month is set */
+  switch (month) {
+    case 1: case 3: case 5: case 7: case 8: case 10: case 12:
+      max_days = 31;
+      break;
+    case 2:
+      /* definition of a leap year: Every fourth year is a leap year expect if year%100 is 0 e.g. 1900
+       * but every year where year%400 is 0 is a leap year again e.g. 2000 */
+      if ((year%4==0 && year%100!=0) || year%400==0) {
+        max_days = 29;
+      }
+      else {
+        max_days = 28;
+      }
+      break;
+  }
+  return max_days;
+}
+
 
 /* Get current time and date and return as a pointer to an array */
 void calc_time_utc (int *time_utc)
 {
   time_t t;
+  struct tm tmp_local;
   struct tm *tmp;
 
-  t = time(NULL);
+  t = time(&t);
+
+  tmp = localtime(&t);
+  memcpy(&tmp_local, tmp, sizeof(struct tm));
   tmp = gmtime(&t);
 
-  g_print ("UTC: %02d:%02d:%02d - %d.%d.%d\n", tmp->tm_hour, tmp->tm_min, tmp->tm_sec, tmp->tm_mday, tmp->tm_mon+1, tmp->tm_year+1900);
+  int time_zone = times_to_zone (tmp->tm_mday, tmp->tm_hour, tmp_local.tm_mday, tmp_local.tm_hour);
+
+  g_print ("UTC: %02d:%02d:%02d - %d.%d.%d, Time zone: %d\n", tmp->tm_hour, tmp->tm_min, tmp->tm_sec, tmp->tm_mday, tmp->tm_mon+1, tmp->tm_year+1900, time_zone);
 
   *(time_utc) = tmp->tm_year+1900;
   *(time_utc+1) = tmp->tm_mon+1;
@@ -31,6 +94,7 @@ void calc_time_utc (int *time_utc)
   *(time_utc+3) = tmp->tm_hour;
   *(time_utc+4) = tmp->tm_min;
   *(time_utc+5) = tmp->tm_sec;
+  *(time_utc+6) = time_zone;
   g_print ("Time calculated");
 }
 

src/calculations.h

@@ -6,6 +6,12 @@ float calc_deg_rad (float deg);
 
 float calc_rad_deg (float rad);
 
+int times_to_zone (int day_utc, int hour_utc, int day_local, int hour_local);
+
+void utc_zone_to_time (int *time_utc, int *time_local);
+
+int max_day_in_month (int month, int year);
+
 void calc_time_utc (int *time_utc);
 
 void calc_jd (int *time_utc, double *time_jd);

src/main.c

@@ -105,23 +105,7 @@ static int correct_time (GtkWidget *widget, gpointer data){
   entry_month_string = gtk_combo_box_get_active_id (entry_month);
   entry_year_double = gtk_spin_button_get_value (entry_year);
 
-  int max_days = 30;
-  /* check which month is set */
-  switch (atoi(entry_month_string)) {
-    case 1: case 3: case 5: case 7: case 8: case 10: case 12:
-      max_days = 31;
-      break;
-    case 2:
-      /* definition of a leap year: Every fourth year is a leap year expect if year%100 is 0 e.g. 1900
-       * but every year where year%400 is 0 is a leap year again e.g. 2000 */
-      if (((int)entry_year_double%4==0 && (int)entry_year_double%100!=0) || (int)entry_year_double%400==0) {
-        max_days = 29;
-      }
-      else {
-        max_days = 28;
-      }
-      break;
-  }
+  int max_days = max_day_in_month (atoi(entry_month_string), (int)entry_year_double);
 
   /* adjust the max. day that can be set */
   GtkAdjustment *d_adjust;
@@ -141,7 +125,7 @@ static int correct_time (GtkWidget *widget, gpointer data){
 
 static int set_time_now (GtkWidget *widget, gpointer data){
   g_print("Now\n");
-  int time_utc_now[6];
+  int time_utc_now[7];
   calc_time_utc (time_utc_now);
   gtk_spin_button_set_value (entry_year, time_utc_now[0]);
   gtk_combo_box_set_active (entry_month, time_utc_now[1]-1);
@@ -170,7 +154,7 @@ static int calculate (GtkWidget *widget, gpointer data)
   float longitude = atof(east_entry_string);
   g_print("Calculation ongoing\n");
 
-  int time_utc_now[6];
+  int time_utc_now[7];
   calc_time_utc (time_utc_now);
   hand_milky_way (latitude, longitude, time_utc_now);
   return 1;