Simplify Julian Date Computations

src/defs.h

@@ -43,6 +43,8 @@
 #define SECONDS_PER_DAY 8.6400E4
 ///Difference between libpredict's predict_julian_date_t and the julian time format used in some of the internal functions
 #define JULIAN_TIME_DIFF 2444238.5
+///Unix timeststamp of 1979-12-31 00:00:00
+#define JULIAN_START_DAY 315446400
 ///@}
 
 /** \name Physical properties

src/julian_date.c

@@ -5,76 +5,14 @@
 
 #include "defs.h"
 
-/**
- * Create time_t in UTC from struct tm.
- *
- * \param timeinfo_utc Broken down time, assumed to be in UTC
- * \return Time in UTC
- **/
-time_t mktime_utc(const struct tm* timeinfo_utc)
-{
- time_t curr_time = time(NULL);
- int timezone_diff = 0; //deviation of the current timezone from UTC in seconds
-
- //get UTC time, interpret resulting tm as a localtime
- struct tm timeinfo_gmt;
- gmtime_r(&curr_time, &timeinfo_gmt);
- time_t time_gmt = mktime(&timeinfo_gmt);
-
- //get localtime, interpret resulting tm as localtime
- struct tm timeinfo_local;
- localtime_r(&curr_time, &timeinfo_local);
- time_t time_local = mktime(&timeinfo_local);
-
- //find the time difference between the two interpretations
- timezone_diff += difftime(time_local, time_gmt);
-
- //hack for preventing mktime from assuming localtime: add timezone difference to the input struct.
- struct tm ret_timeinfo;
- ret_timeinfo.tm_sec = timeinfo_utc->tm_sec + timezone_diff;
- ret_timeinfo.tm_min = timeinfo_utc->tm_min;
- ret_timeinfo.tm_hour = timeinfo_utc->tm_hour;
- ret_timeinfo.tm_mday = timeinfo_utc->tm_mday;
- ret_timeinfo.tm_mon = timeinfo_utc->tm_mon;
- ret_timeinfo.tm_year = timeinfo_utc->tm_year;
- ret_timeinfo.tm_isdst = timeinfo_utc->tm_isdst;
- return mktime(&ret_timeinfo);
-}
-
-/**
- * Helper function for getting the Julian day start date (1979-12-31 00:00 UTC) as time_t.
- *
- * \return Internally defined Julian start date (fixed)
- **/
-time_t get_julian_start_day()
-{
- struct tm start_time;
- start_time.tm_sec = 0;
- start_time.tm_min = 0;
- start_time.tm_hour = 0;
- start_time.tm_mday = 31;
- start_time.tm_mon = 11;
- start_time.tm_year = 1979-1900;
- start_time.tm_isdst = 0;
- return mktime_utc(&start_time);
-}
-
 predict_julian_date_t predict_to_julian(time_t input_time)
 {
  //get number of seconds since 1979-12-31 00:00:00 UTC, convert to days
- double seconds = difftime(input_time, get_julian_start_day());
+ double seconds = difftime(input_time, JULIAN_START_DAY);
  return seconds/SECONDS_PER_DAY;
 }
 
 time_t predict_from_julian(predict_julian_date_t date)
 {
- double seconds_since = date*SECONDS_PER_DAY;
- time_t ret_time = get_julian_start_day();
-
- //add number of seconds since julian start day to the julian start day, get current time_t
- struct tm timeinfo;
- gmtime_r(&ret_time, &timeinfo); 
- timeinfo.tm_sec += seconds_since;
- ret_time = mktime_utc(&timeinfo);
- return ret_time;
+ return date * SECONDS_PER_DAY + JULIAN_START_DAY;
 }