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87 lines
1.7 KiB
C
87 lines
1.7 KiB
C
#include <time.h>
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// from musl@1cc81f5cb, slightly tweaked
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static long long
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__year_to_secs(long long year, int *is_leap)
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{
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if (year-2ULL <= 136) {
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int y = year;
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int leaps = (y-68)>>2;
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if (!((y-68)&3)) {
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leaps--;
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if (is_leap) *is_leap = 1;
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} else if (is_leap) *is_leap = 0;
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return 31536000*(y-70) + 86400*leaps;
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}
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int cycles, centuries, leaps, rem;
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cycles = (year-100) / 400;
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rem = (year-100) % 400;
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if (rem < 0) {
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cycles--;
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rem += 400;
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}
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if (!rem) {
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*is_leap = 1;
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centuries = 0;
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leaps = 0;
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} else {
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if (rem >= 200) {
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if (rem >= 300) centuries = 3, rem -= 300;
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else centuries = 2, rem -= 200;
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} else {
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if (rem >= 100) centuries = 1, rem -= 100;
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else centuries = 0;
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}
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if (!rem) {
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*is_leap = 0;
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leaps = 0;
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} else {
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leaps = rem / 4U;
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rem %= 4U;
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*is_leap = !rem;
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}
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}
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leaps += 97*cycles + 24*centuries - *is_leap;
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return (year-100) * 31536000LL + leaps * 86400LL + 946684800 + 86400;
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}
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static int
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__month_to_secs(int month, int is_leap)
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{
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static const int secs_through_month[] = {
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0, 31*86400, 59*86400, 90*86400,
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120*86400, 151*86400, 181*86400, 212*86400,
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243*86400, 273*86400, 304*86400, 334*86400 };
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int t = secs_through_month[month];
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if (is_leap && month >= 2) t+=86400;
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return t;
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}
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time_t tm_to_secs(const struct tm *tm)
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{
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int is_leap;
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long long year = tm->tm_year;
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int month = tm->tm_mon;
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if (month >= 12 || month < 0) {
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int adj = month / 12;
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month %= 12;
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if (month < 0) {
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adj--;
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month += 12;
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}
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year += adj;
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}
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long long t = __year_to_secs(year, &is_leap);
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t += __month_to_secs(month, is_leap);
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t += 86400LL * (tm->tm_mday-1);
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t += 3600LL * tm->tm_hour;
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t += 60LL * tm->tm_min;
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t += tm->tm_sec;
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return t;
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}
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