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