#define _GNU_SOURCE
#include <time.h>
/* this is cut and paste from mktime. */
extern const short __spm [];
time_t timegm(struct tm *const t) {
register time_t day;
register time_t i;
register time_t years = t->tm_year - 70;
if (t->tm_sec>60) { t->tm_min += t->tm_sec/60; t->tm_sec%=60; }
if (t->tm_min>60) { t->tm_hour += t->tm_min/60; t->tm_min%=60; }
if (t->tm_hour>60) { t->tm_mday += t->tm_hour/60; t->tm_hour%=60; }
if (t->tm_mon>12) { t->tm_year += t->tm_mon/12; t->tm_mon%=12; }
if (t->tm_mon<0) t->tm_mon=0;
while (t->tm_mday>__spm[1+t->tm_mon]) {
if (t->tm_mon==1 && __isleap(t->tm_year+1900)) {
if (t->tm_mon==31+29) break;
--t->tm_mday;
}
t->tm_mday-=__spm[t->tm_mon];
++t->tm_mon;
if (t->tm_mon>11) { t->tm_mon=0; ++t->tm_year; }
}
if (t->tm_year < 70)
return (time_t) -1;
/* Days since 1970 is 365 * number of years + number of leap years since 1970 */
day = years * 365 + (years + 1) / 4;
/* After 2100 we have to substract 3 leap years for every 400 years
This is not intuitive. Most mktime implementations do not support
dates after 2059, anyway, so we might leave this out for it's
bloat. */
if ((years -= 131) >= 0) {
years /= 100;
day -= (years >> 2) * 3 + 1;
if ((years &= 3) == 3) years--;
day -= years;
}
day += t->tm_yday = __spm [t->tm_mon] + t->tm_mday-1 + ( __isleap (t->tm_year+1900) & (t->tm_mon > 1) );
/* day is now the number of days since 'Jan 1 1970' */
i = 7;
t->tm_wday = (day + 4) % i; /* Sunday=0, Monday=1, ..., Saturday=6 */
i = 24;
day *= i;
i = 60;
return ((day + t->tm_hour) * i + t->tm_min) * i + t->tm_sec;
}
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