FOUR_DIGIT_YEAR()

#define FOUR_DIGIT_YEAR(y) ((y < 50)? y + 2000 : y + 1900)

epoch_day_from_ymd ()

guint32
epoch_day_from_ymd (int y,
                    int m,
                    int d);

epoch_day_from_ymd_basic ()

guint32
epoch_day_from_ymd_basic (double ymd);

epoch_day_from_ymd_checked ()

guint32
epoch_day_from_ymd_checked (double ymd,
                            int *err);

epoch_day_from_julian_ymd ()

guint32
epoch_day_from_julian_ymd (int y,
                           int m,
                           int d);

The y , m and d arguments are assumed to refer to a date on the Julian calendar. The conversion algorithm is taken from https://en.wikipedia.org/wiki/Julian_day, where it appears to be credited to the Department of Computer Science at UT, Austin.

nearby_epoch_day ()

guint32
nearby_epoch_day (int y,
                  int m,
                  int d,
                  int wkdays);

ymd_extended_from_epoch_day ()

char *
ymd_extended_from_epoch_day (guint32 ed,
                             int julian,
                             int *err);

ymd_basic_from_epoch_day ()

double
ymd_basic_from_epoch_day (guint32 ed,
                          int julian,
                          int *err);

ymd_bits_from_epoch_day ()

int
ymd_bits_from_epoch_day (guint32 ed,
                         int *y,
                         int *m,
                         int *d);

julian_ymd_bits_from_epoch_day ()

int
julian_ymd_bits_from_epoch_day (guint32 ed,
                                int *y,
                                int *m,
                                int *d);

Follows the algorithm of E.G. Richards (2013), "Calendars," In S.E. Urban & P.K. Seidelmann, eds. Explanatory Supplement to the Astronomical Almanac, 3rd ed. (pp. 585-624), Mill Valley, CA: University Science Books (as set out on https://en.wikipedia.org/wiki/Julian_day).

There are other algorithms for this purpose on the internet but they are mostly wrong (at least, not right for all dates); many of them fail the round-trip test (date -> epoch day -> date) for some dates.

iso_basic_to_extended ()

int
iso_basic_to_extended (const double *b,
                       double *y,
                       double *m,
                       double *d,
                       int n);

Given the array b of ISO 8601 "basic" daily dates (YYYYMMDD as doubles), fill out the arrays y , m and d with year, month and day.

get_epoch_day ()

guint32
get_epoch_day (const char *datestr);

epoch_day_from_t ()

guint32
epoch_day_from_t (int t,
                  const DATASET *dset);

weekday_from_date ()

int
weekday_from_date (const char *datestr);

weekday_from_epoch_day ()

int
weekday_from_epoch_day (guint32 ed);

day_starts_month ()

int
day_starts_month (int d,
                  int m,
                  int y,
                  int wkdays,
                  int *pad);

day_ends_month ()

int
day_ends_month (int d,
                int m,
                int y,
                int wkdays);

get_days_in_month ()

int
get_days_in_month (int m,
                   int y,
                   int wkdays,
                   int julian);

month_day_index ()

int
month_day_index (int y,
                 int m,
                 int d,
                 int wkdays);

days_in_month_before ()

int
days_in_month_before (int y,
                      int m,
                      int d,
                      int wkdays);

days_in_month_after ()

int
days_in_month_after (int y,
                     int m,
                     int d,
                     int wkdays);

date_to_daily_index ()

int
date_to_daily_index (const char *datestr,
                     int wkdays);

daily_index_to_date ()

int
daily_index_to_date (char *targ,
                     int y,
                     int m,
                     int idx,
                     int wkdays);

Fills out targ with the calendar data implied by the specification of y , m , seq and wkdays , provided this specification corresponds to an actual calendar date.

calendar_obs_number ()

int
calendar_obs_number (const char *datestr,
                     const DATASET *dset);

calendar_date_string ()

int
calendar_date_string (char *targ,
                      int t,
                      const DATASET *dset);

Writes to targ the calendar representation of the date of observation t , in the form YY[YY]-MM-DD.

MS_excel_date_string ()

int
MS_excel_date_string (char *targ,
                      int mst,
                      int pd,
                      int d1904);

Writes to targ the calendar representation of the date of observation mst , in the form YYYY-MM-DD if pd is 0, 5, 6, 7 or 52 (unknown, daily, or weekly frequency), otherwise in the appropriate format for annual, quarterly or monthly according to pd .

get_dec_date ()

double
get_dec_date (const char *datestr);

day_of_week ()

double
day_of_week (int y,
             int m,
             int d,
             int julian,
             int *err);

n_hidden_missing_obs ()

int
n_hidden_missing_obs (const DATASET *dset,
                      int t1,
                      int t2);

For daily data with user-supplied data strings, determine the number of "hidden" missing observations in the range t1 to t2 inclusive. This is the difference between the actual number of observations and the number that should be there, according to the calendar. Allowance is made for 5- or 6-day data, via the data frequency given in dset .

guess_daily_pd ()

int
guess_daily_pd (const DATASET *dset);

Based on user-supplied daily date strings recorded in dset , try to guess whether the number of observations per week is 5, 6 or 7 (given that some observations may be missing).

easterdate ()

double
easterdate (int year);

Algorithm taken from Wikipedia page https://en.wikipedia.org/wiki/Computus under the heading "Anonymous Gregorian algorithm".

day_span ()

int
day_span (guint32 ed1,
          guint32 ed2,
          int wkdays,
          int *err);

iso_week_number ()

int
iso_week_number (int y,
                 int m,
                 int d,
                 int *err);

iso_week_from_date ()

int
iso_week_from_date (const char *datestr);

fill_monthlen_array ()

int
fill_monthlen_array (double *mlen,
                     int t1,
                     int t2,
                     int wkdays,
                     int mo,
                     int yr,
                     const double *movec,
                     const double *yrvec,
                     int julian);

Fills mlen from t1 to t2 with the number of days in each month/year pair. It is assumed that at least one of movec and yrvec is non-NULL. The various arrays are doubles only because in context they will be dataset series; in concept they are integers.

gretl_strfdate ()

int
gretl_strfdate (char *s,
                int slen,
                const char *format,
                guint32 ed);

If ed is found to be valid, writes a string representing the date of ed to s , governed by format .

gretl_alt_strfdate ()

int
gretl_alt_strfdate (char *s,
                    int slen,
                    int julian,
                    guint32 ed);

If ed is found to be valid, writes a string representing the date of ed to s , as ISO 8601 extended.

gretl_strftime ()

int
gretl_strftime (char *s,
                int slen,
                const char *format,
                gint64 t,
                double off_secs);

If t and format are found to be valid, writes a string representing the date and time of t to s , governed by format . If off_secs is NADBL it is ignored, and the date and time on output are relative to local time. Otherwise date and time are relative to the time zone defined by off_secs (and so a zero value gives UTC).

gretl_strptime ()

char *
gretl_strptime (const char *s,
                const char *format,
                double *dt);