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{
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