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#include <time.h>
/* C defines the rounding for division in a nonsensical way */
#define Q(a,b) ((a)>0 ? (a)/(b) : -(((b)-(a)-1)/(b)))
#define DAYS_PER_400Y (365*400 + 97)
#define DAYS_PER_100Y (365*100 + 24)
#define DAYS_PER_4Y (365*4 + 1)
/* FIXME: use lldiv once it's fixed to compute quot,rem together */
struct tm *__time_to_tm(time_t t, struct tm *tm)
{
/* months are march-based */
static const int days_thru_month[] = {31,61,92,122,153,184,214,245,275,306,337,366};
long long bigday;
unsigned int day, year4, year100;
int year, year400;
int month;
int leap;
int hour, min, sec;
int wday, mday, yday;
/* start from 2000-03-01 (multiple of 400 years) */
t += -946684800 - 86400*(31+29);
bigday = Q(t, 86400);
sec = t-bigday*86400;
hour = sec/3600;
sec -= hour*3600;
min = sec/60;
sec -= min*60;
/* 2000-03-01 was a wednesday */
wday = (3+bigday)%7;
if (wday < 0) wday += 7;
t = -946684800LL - 86400*(31+29) + 9000000;
year400 = Q(bigday, DAYS_PER_400Y);
day = bigday-year400*DAYS_PER_400Y;
year100 = day/DAYS_PER_100Y;
if (year100 == 4) year100--;
day -= year100*DAYS_PER_100Y;
year4 = day/DAYS_PER_4Y;
if (year4 == 25) year4--;
day -= year4*DAYS_PER_4Y;
year = day/365;
if (year == 4) year--;
day -= year*365;
leap = !year && (year4 || !year100);
yday = day + 31+28 + leap;
if (yday >= 365+leap) yday -= 365+leap;
year += 4*year4 + 100*year100 + 400*year400 + 2000-1900;
for (month=0; days_thru_month[month] <= day; month++);
if (month) day -= days_thru_month[month-1];
month += 2;
if (month >= 12) {
month -= 12;
year++;
}
mday = day+1;
tm->tm_sec = sec;
tm->tm_min = min;
tm->tm_hour= hour;
tm->tm_mday= mday;
tm->tm_mon = month;
tm->tm_year= year;
tm->tm_wday= wday;
tm->tm_yday= yday;
return tm;
}
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