diff options
Diffstat (limited to 'src/time/__secs_to_tm.c')
-rw-r--r-- | src/time/__secs_to_tm.c | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/src/time/__secs_to_tm.c b/src/time/__secs_to_tm.c new file mode 100644 index 00000000..f3c1cf92 --- /dev/null +++ b/src/time/__secs_to_tm.c @@ -0,0 +1,81 @@ +#include "time_impl.h" +#include <limits.h> + +/* 2000-03-01 (mod 400 year, immediately after feb29 */ +#define LEAPOCH (946684800LL + 86400*(31+29)) + +#define DAYS_PER_400Y (365*400 + 97) +#define DAYS_PER_100Y (365*100 + 24) +#define DAYS_PER_4Y (365*4 + 1) + +int __secs_to_tm(long long t, struct tm *tm) +{ + long long days, secs; + int remdays, remsecs, remyears; + int qc_cycles, c_cycles, q_cycles; + int years, months; + int wday, yday, leap; + static const char days_in_month[] = {31,30,31,30,31,31,30,31,30,31,31,29}; + + /* Reject time_t values whose year would overflow int */ + if (t < INT_MIN * 31622400LL || t > INT_MAX * 31622400LL) + return -1; + + secs = t - LEAPOCH; + days = secs / 86400; + remsecs = secs % 86400; + if (remsecs < 0) { + remsecs += 86400; + days--; + } + + wday = (3+days)%7; + if (wday < 0) wday += 7; + + qc_cycles = days / DAYS_PER_400Y; + remdays = days % DAYS_PER_400Y; + if (remdays < 0) { + remdays += DAYS_PER_400Y; + qc_cycles--; + } + + c_cycles = remdays / DAYS_PER_100Y; + if (c_cycles == 4) c_cycles--; + remdays -= c_cycles * DAYS_PER_100Y; + + q_cycles = remdays / DAYS_PER_4Y; + if (q_cycles == 25) q_cycles--; + remdays -= q_cycles * DAYS_PER_4Y; + + remyears = remdays / 365; + if (remyears == 4) remyears--; + remdays -= remyears * 365; + + leap = !remyears && (q_cycles || !c_cycles); + yday = remdays + 31 + 28 + leap; + if (yday >= 365+leap) yday -= 365+leap; + + years = remyears + 4*q_cycles + 100*c_cycles + 400*qc_cycles; + + for (months=0; days_in_month[months] <= remdays; months++) + remdays -= days_in_month[months]; + + if (years+100 > INT_MAX || years+100 < INT_MIN) + return -1; + + tm->tm_year = years + 100; + tm->tm_mon = months + 2; + if (tm->tm_mon >= 12) { + tm->tm_mon -=12; + tm->tm_year++; + } + tm->tm_mday = remdays + 1; + tm->tm_wday = wday; + tm->tm_yday = yday; + + tm->tm_hour = remsecs / 3600; + tm->tm_min = remsecs / 60 % 60; + tm->tm_sec = remsecs % 60; + + return 0; +} |