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	ctime.c - 9base - revived minimalist port of Plan 9 userland to Unix
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	---
	ctime.c (3082B)
	---
	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);
	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 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 }
	181