1 /*
2  * This routine converts time as follows.
3  * The epoch is 0000 Jan 1 1970 GMT.
4  * The argument time is in seconds since then.
5  * The localtime(t) entry returns a pointer to an array
6  * containing
7  *
8  *	seconds (0-59)
9  *	minutes (0-59)
10  *	hours (0-23)
11  *	day of month (1-31)
12  *	month (0-11)
13  *	year-1970
14  *	weekday (0-6, Sun is 0)
15  *	day of the year
16  *	daylight savings flag
17  *
18  * The routine gets the daylight savings time from the environment.
19  *
20  * asctime(tvec))
21  * where tvec is produced by localtime
22  * returns a ptr to a character string
23  * that has the ascii time in the form
24  *
25  *	                            \\
26  *	Thu Jan 01 00:00:00 GMT 1970n0
27  *	012345678901234567890123456789
28  *	0	  1	    2
29  *
30  * ctime(t) just calls localtime, then asctime.
31  */
32 
33 #include <u.h>
34 #include <libc.h>
35 
36 #include "zoneinfo.h"
37 
38 static	char	dmsize[12] =
39 {
40 	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
41 };
42 
43 #define dysize ctimedysize
44 static	int	dysize(int);
45 static	void	ct_numb(char*, int);
46 
47 char*
48 ctime(long t)
49 {
50 	return asctime(localtime(t));
51 }
52 
53 Tm*
54 localtime(long tim)
55 {
56 	Tinfo ti;
57 	Tm *ct;
58 
59 	if (zonelookuptinfo(&ti, tim)!=-1) {
60 		ct = gmtime(tim+ti.tzoff);
61 		strncpy(ct->zone, ti.zone, sizeof ct->zone - 1);
62 		ct->zone[sizeof ct->zone-1] = 0;
63 		ct->tzoff = ti.tzoff;
64 		return ct;
65 	}
66 	return gmtime(tim);
67 }
68 
69 Tm*
70 gmtime(long tim)
71 {
72 	int d0, d1;
73 	long hms, day;
74 	static Tm xtime;
75 
76 	/*
77 	 * break initial number into days
78 	 */
79 	hms = tim % 86400L;
80 	day = tim / 86400L;
81 	if(hms < 0) {
82 		hms += 86400L;
83 		day -= 1;
84 	}
85 
86 	/*
87 	 * generate hours:minutes:seconds
88 	 */
89 	xtime.sec = hms % 60;
90 	d1 = hms / 60;
91 	xtime.min = d1 % 60;
92 	d1 /= 60;
93 	xtime.hour = d1;
94 
95 	/*
96 	 * day is the day number.
97 	 * generate day of the week.
98 	 * The addend is 4 mod 7 (1/1/1970 was Thursday)
99 	 */
100 
101 	xtime.wday = (day + 7340036L) % 7;
102 
103 	/*
104 	 * year number
105 	 */
106 	if(day >= 0)
107 		for(d1 = 1970; day >= dysize(d1); d1++)
108 			day -= dysize(d1);
109 	else
110 		for (d1 = 1970; day < 0; d1--)
111 			day += dysize(d1-1);
112 	xtime.year = d1-1900;
113 	xtime.yday = d0 = day;
114 
115 	/*
116 	 * generate month
117 	 */
118 
119 	if(dysize(d1) == 366)
120 		dmsize[1] = 29;
121 	for(d1 = 0; d0 >= dmsize[d1]; d1++)
122 		d0 -= dmsize[d1];
123 	dmsize[1] = 28;
124 	xtime.mday = d0 + 1;
125 	xtime.mon = d1;
126 	strcpy(xtime.zone, "GMT");
127 	return &xtime;
128 }
129 
130 char*
131 asctime(Tm *t)
132 {
133 	const char *ncp;
134 	static char cbuf[30];
135 
136 	strcpy(cbuf, "Thu Jan 01 00:00:00 GMT 1970\n");
137 	ncp = &"SunMonTueWedThuFriSat"[t->wday*3];
138 	cbuf[0] = *ncp++;
139 	cbuf[1] = *ncp++;
140 	cbuf[2] = *ncp;
141 	ncp = &"JanFebMarAprMayJunJulAugSepOctNovDec"[t->mon*3];
142 	cbuf[4] = *ncp++;
143 	cbuf[5] = *ncp++;
144 	cbuf[6] = *ncp;
145 	ct_numb(cbuf+8, t->mday);
146 	ct_numb(cbuf+11, t->hour+100);
147 	ct_numb(cbuf+14, t->min+100);
148 	ct_numb(cbuf+17, t->sec+100);
149 	ncp = t->zone;
150 	cbuf[20] = *ncp++;
151 	cbuf[21] = *ncp++;
152 	cbuf[22] = *ncp;
153 	if(t->year >= 100) {
154 		cbuf[24] = '2';
155 		cbuf[25] = '0';
156 	}
157 	ct_numb(cbuf+26, t->year+100);
158 	return cbuf;
159 }
160 
161 static
162 int
163 dysize(int y)
164 {
165 
166 	if(y%4 == 0 && (y%100 != 0 || y%400 == 0))
167 		return 366;
168 	return 365;
169 }
170 
171 static
172 void
173 ct_numb(char *cp, int n)
174 {
175 
176 	cp[0] = ' ';
177 	if(n >= 10)
178 		cp[0] = (n/10)%10 + '0';
179 	cp[1] = n%10 + '0';
180 }