static char daytab[2][13] = {
     {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
     {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
};

/* set day of year from month & day */
int day_of_year(int year, int month, int day) {
     int i, leap;

     if ((month <= 0 || month > 12) ||
	 (day <= 0 || day > 31) ||
	 (year < 0))
	  return -1;
     leap = year%4 == 0 && year%100 != 0 || year%400 == 0;
     for (i = 1; i < month; i++)
	  day += daytab[leap][i];
     return day;
}

/* set month, day from day of year */
void month_day(int year, int yearday, int *pmonth, int *pday) {
     int i, leap;

     if ((year < 0) ||
	 (yearday <= 0 || yearday > 366)) {
	  *pmonth = -1;
	  *pday = -1;
	  return;
     }
     leap = year%4 == 0 && year%100 != 0 || year%400 == 0;
     for (i = 1; yearday > daytab[leap][i]; i++)
	  yearday -= daytab[leap][i];
     *pmonth = i;
     *pday = yearday;
}

/* set day of year from month & day, pointer version */
int pday_of_year(int year, int month, int day) {
     int leap;
     char *daytp[][] = daytab;

     if ((month <= 0 || month > 12) ||
	 (day <= 0 || day > 31) ||
	 (year < 0))
	  return -1;
     leap = year%4 == 0 && year%100 != 0 || year%400 == 0;
     while (daytp[leap] < daytab[leap] + month + 1)
	  day += *daytp[leap]++;
     return day;
}

/* set month, day from day of year, pointer version */
void pmonth_day(int year, int yearday, int *pmonth, int *pday) {
     int leap;
     char *daytp[][] = daytab;

     if ((year < 0) ||
	 (yearday <= 0 || yearday > 366)) {
	  *pmonth = -1;
	  *pday = -1;
	  return;
     }
     leap = year%4 == 0 && year%100 != 0 || year%400 == 0;
     while (yearday > *daytab[leap])
	  yearday -= *daytp[leap]++;
     *pmonth = daytp[leap] - daytab[leap];
     *pday = yearday;
}