1#include "time_impl.h" 2#include <limits.h> 3 4/* 2000-03-01 (mod 400 year, immediately after feb29 */ 5#define LEAPOCH (946684800LL + 86400 * (31 + 29)) 6 7#define DAYS_PER_400Y (365 * 400 + 97) 8#define DAYS_PER_100Y (365 * 100 + 24) 9#define DAYS_PER_4Y (365 * 4 + 1) 10 11int __secs_to_tm(long long t, struct tm* tm) { 12 long long days, secs, years; 13 int remdays, remsecs, remyears; 14 int qc_cycles, c_cycles, q_cycles; 15 int months; 16 int wday, yday, leap; 17 static const char days_in_month[] = {31, 30, 31, 30, 31, 31, 30, 31, 30, 31, 31, 29}; 18 19 /* Reject time_t values whose year would overflow int */ 20 if (t < INT_MIN * 31622400LL || t > INT_MAX * 31622400LL) 21 return -1; 22 23 secs = t - LEAPOCH; 24 days = secs / 86400; 25 remsecs = secs % 86400; 26 if (remsecs < 0) { 27 remsecs += 86400; 28 days--; 29 } 30 31 wday = (3 + days) % 7; 32 if (wday < 0) 33 wday += 7; 34 35 qc_cycles = days / DAYS_PER_400Y; 36 remdays = days % DAYS_PER_400Y; 37 if (remdays < 0) { 38 remdays += DAYS_PER_400Y; 39 qc_cycles--; 40 } 41 42 c_cycles = remdays / DAYS_PER_100Y; 43 if (c_cycles == 4) 44 c_cycles--; 45 remdays -= c_cycles * DAYS_PER_100Y; 46 47 q_cycles = remdays / DAYS_PER_4Y; 48 if (q_cycles == 25) 49 q_cycles--; 50 remdays -= q_cycles * DAYS_PER_4Y; 51 52 remyears = remdays / 365; 53 if (remyears == 4) 54 remyears--; 55 remdays -= remyears * 365; 56 57 leap = !remyears && (q_cycles || !c_cycles); 58 yday = remdays + 31 + 28 + leap; 59 if (yday >= 365 + leap) 60 yday -= 365 + leap; 61 62 years = remyears + 4 * q_cycles + 100 * c_cycles + 400LL * qc_cycles; 63 64 for (months = 0; days_in_month[months] <= remdays; months++) 65 remdays -= days_in_month[months]; 66 67 if (years + 100 > INT_MAX || years + 100 < INT_MIN) 68 return -1; 69 70 tm->tm_year = years + 100; 71 tm->tm_mon = months + 2; 72 if (tm->tm_mon >= 12) { 73 tm->tm_mon -= 12; 74 tm->tm_year++; 75 } 76 tm->tm_mday = remdays + 1; 77 tm->tm_wday = wday; 78 tm->tm_yday = yday; 79 80 tm->tm_hour = remsecs / 3600; 81 tm->tm_min = remsecs / 60 % 60; 82 tm->tm_sec = remsecs % 60; 83 84 return 0; 85} 86