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/*

 * This routine converts time as follows.

 * The epoch is 0000 Jan 1 1970 GMT.

 * The argument time is in seconds since then.

 * The localtime(t) entry returns a pointer to an array

 * containing

 *

 *	seconds (0-59)

 *	minutes (0-59)

 *	hours (0-23)

 *	day of month (1-31)

 *	month (0-11)

 *	year-1970

 *	weekday (0-6, Sun is 0)

 *	day of the year

 *	daylight savings flag

 *

 * The routine gets the daylight savings time from the environment.

 *

 * asctime(tvec))

 * where tvec is produced by localtime

 * returns a ptr to a character string

 * that has the ascii time in the form

 *

 *	                            \\

 *	Thu Jan 01 00:00:00 GMT 1970n0

 *	012345678901234567890123456789

 *	0	  1	    2

 *

 * ctime(t) just calls localtime, then asctime.

 */

#include <u.h>

#include <libc.h>

static	char	dmsize[12] =

{

	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31

};

/*

 * The following table is used for 1974 and 1975 and

 * gives the day number of the first day after the Sunday of the

 * change.

 */

static	int	dysize(int);

static	void	ct_numb(char*, int);

#define	TZSIZE	150

static	void	readtimezone(void);

static	int	rd_name(char**, char*);

static	int	rd_long(char**, long*);

static

struct

{

	char	stname[4];

	char	dlname[4];

	long	stdiff;

	long	dldiff;

	long	dlpairs[TZSIZE];

} timezone;

char*

ctime(long t)

{

	return asctime(localtime(t));

}

Tm*

localtime(long tim)

{

	Tm *ct;

	long t, *p;

	int dlflag;

	if(timezone.stname[0] == 0)

		readtimezone();

	t = tim + timezone.stdiff;

	dlflag = 0;

	for(p = timezone.dlpairs; *p; p += 2)

		if(t >= p[0])

		if(t < p[1]) {

			t = tim + timezone.dldiff;

			dlflag++;

			break;

		}

	ct = gmtime(t);

	if(dlflag){

		strcpy(ct->zone, timezone.dlname);

		ct->tzoff = timezone.dldiff;

	} else {

		strcpy(ct->zone, timezone.stname);

		ct->tzoff = timezone.stdiff;

	}

	return ct;

}

Tm*

gmtime(long tim)

{

	int d0, d1;

	long hms, day;

	static Tm xtime;

	/*

	 * break initial number into days

	 */

	hms = (ulong)tim % 86400L;

	day = (ulong)tim / 86400L;

	if(hms < 0) {

		hms += 86400L;

		day -= 1;

	}

	/*

	 * generate hours:minutes:seconds

	 */

	xtime.sec = hms % 60;

	d1 = hms / 60;

	xtime.min = d1 % 60;

	d1 /= 60;

	xtime.hour = d1;

	/*

	 * day is the day number.

	 * generate day of the week.

	 * The addend is 4 mod 7 (1/1/1970 was Thursday)

	 */

	xtime.wday = (day + 7340036L) % 7;

	/*

	 * year number

	 */

	if(day >= 0)

		for(d1 = 1970; day >= dysize(d1); d1++)

			day -= dysize(d1);

	else

		for (d1 = 1970; day < 0; d1--)

			day += dysize(d1-1);

	xtime.year = d1-1900;

	xtime.yday = d0 = day;

	/*

	 * generate month

	 */

	if(dysize(d1) == 366)

		dmsize[1] = 29;

	for(d1 = 0; d0 >= dmsize[d1]; d1++)

		d0 -= dmsize[d1];

	dmsize[1] = 28;

	xtime.mday = d0 + 1;

	xtime.mon = d1;

	strcpy(xtime.zone, "GMT");

	return &xtime;

}

char*

asctime(Tm *t)

{

	char *ncp;

	static char cbuf[30];

	strcpy(cbuf, "Thu Jan 01 00:00:00 GMT 1970\n");

	ncp = &"SunMonTueWedThuFriSat"[t->wday*3];

	cbuf[0] = *ncp++;

	cbuf[1] = *ncp++;

	cbuf[2] = *ncp;

	ncp = &"JanFebMarAprMayJunJulAugSepOctNovDec"[t->mon*3];

	cbuf[4] = *ncp++;

	cbuf[5] = *ncp++;

	cbuf[6] = *ncp;

	ct_numb(cbuf+8, t->mday);

	ct_numb(cbuf+11, t->hour+100);

	ct_numb(cbuf+14, t->min+100);

	ct_numb(cbuf+17, t->sec+100);

	ncp = t->zone;

	cbuf[20] = *ncp++;

	cbuf[21] = *ncp++;

	cbuf[22] = *ncp;

	if(t->year >= 100) {

		cbuf[24] = '2';

		cbuf[25] = '0';

	}

	ct_numb(cbuf+26, t->year+100);

	return cbuf;

}

static

dysize(int y)

{

	if(y%4 == 0 && (y%100 != 0 || y%400 == 0))

		return 366;

	return 365;

}

static

void

ct_numb(char *cp, int n)

{

	cp[0] = ' ';

	if(n >= 10)

		cp[0] = (n/10)%10 + '0';

	cp[1] = n%10 + '0';

}

static

void

readtimezone(void)

{

	char buf[TZSIZE*11+30], *p;

	int i;

	memset(buf, 0, sizeof(buf));

	i = open("/env/timezone", 0);

	if(i < 0)

		goto error;

	if(read(i, buf, sizeof(buf)) >= sizeof(buf)){

		close(i);

		goto error;

	}

	close(i);

	p = buf;

	if(rd_name(&p, timezone.stname))

		goto error;

	if(rd_long(&p, &timezone.stdiff))

		goto error;

	if(rd_name(&p, timezone.dlname))

		goto error;

	if(rd_long(&p, &timezone.dldiff))

		goto error;

	for(i=0; i<TZSIZE; i++) {

		if(rd_long(&p, &timezone.dlpairs[i]))

			goto error;

		if(timezone.dlpairs[i] == 0)

			return;

	}

error:

	timezone.stdiff = 0;

	strcpy(timezone.stname, "GMT");

	timezone.dlpairs[0] = 0;

}

static

rd_name(char **f, char *p)

{

	int c, i;

	for(;;) {

		c = *(*f)++;

		if(c != ' ' && c != '\n')

			break;

	}

	for(i=0; i<3; i++) {

		if(c == ' ' || c == '\n')

			return 1;

		*p++ = c;

		c = *(*f)++;

	}

	if(c != ' ' && c != '\n')

		return 1;

	*p = 0;

	return 0;

}

static

rd_long(char **f, long *p)

{

	int c, s;

	long l;

	s = 0;

	for(;;) {

		c = *(*f)++;

		if(c == '-') {

			s++;

			continue;

		}

		if(c != ' ' && c != '\n')

			break;

	}

	if(c == 0) {

		*p = 0;

		return 0;

	}

	l = 0;

	for(;;) {

		if(c == ' ' || c == '\n')

			break;

		if(c < '0' || c > '9')

			return 1;

		l = l*10 + c-'0';

		c = *(*f)++;

	}

	if(s)

		l = -l;

	*p = l;

	return 0;

}