/*
 * 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 calls the system to determine the local
 * timezone and whether Daylight Saving Time is permitted locally.
 * (DST is then determined by the current US standard rules)
 * There is a table that accounts for the peculiarities
 * undergone by daylight time in 1974-1975.
 *
 * The routine does not work
 * in Saudi Arabia which runs on Solar time.
 *
 * 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 1970n0\\
 *	01234567890123456789012345
 *	0	  1	    2
 *
 * ctime(t) just calls localtime, then asctime.
 */

#include <time.h>
#include <sys/types.h>
#include <sys/timeb.h>

static	char	cbuf[26];
static	int	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 struct {
	int	daylb;
	int	dayle;
} daytab[] = {
	5,	333,	/* 1974: Jan 6 - last Sun. in Nov */
	58,	303,	/* 1975: Last Sun. in Feb - last Sun in Oct */
};

struct tm	*gmtime();
char		*ct_numb();
struct tm	*localtime();
char	*ctime();
char	*ct_num();
char	*asctime();

char *
ctime(t)
long *t;
{
	return(asctime(localtime(t)));
}

struct tm *
localtime(tim)
long *tim;
{
	register int dayno;
	register struct tm *ct;
	register daylbegin, daylend;
	long copyt;
	struct timeb systime;

	ftime(&systime);
	copyt = *tim - (long)systime.timezone*60;
	ct = gmtime(&copyt);
	dayno = ct->tm_yday;
	daylbegin = 119;	/* last Sun in Apr */
	daylend = 303;		/* Last Sun in Oct */
	if (ct->tm_year==74 || ct->tm_year==75) {
		daylbegin = daytab[ct->tm_year-74].daylb;
		daylend = daytab[ct->tm_year-74].dayle;
	}
	daylbegin = sunday(ct, daylbegin);
	daylend = sunday(ct, daylend);
	if (systime.dstflag &&
	    (dayno>daylbegin || (dayno==daylbegin && ct->tm_hour>=2)) &&
	    (dayno<daylend || (dayno==daylend && ct->tm_hour<1))) {
		copyt += 1*60*60;
		ct = gmtime(&copyt);
		ct->tm_isdst++;
	}
	return(ct);
}

/*
 * The argument is a 0-origin day number.
 * The value is the day number of the first
 * Sunday on or after the day.
 */
static
sunday(t, d)
register struct tm *t;
register int d;
{
	if (d >= 58)
		d += dysize(t->tm_year) - 365;
	return(d - (d - t->tm_yday + t->tm_wday + 700) % 7);
}

struct tm *
gmtime(tim)
long *tim;
{
	register int d0, d1;
	long hms, day;
	register int *tp;
	static struct tm xtime;

	/*
	 * break initial number into days
	 */
	hms = *tim % 86400;
	day = *tim / 86400;
	if (hms<0) {
		hms += 86400;
		day -= 1;
	}
	tp = (int *)&xtime;

	/*
	 * generate hours:minutes:seconds
	 */
	*tp++ = hms%60;
	d1 = hms/60;
	*tp++ = d1%60;
	d1 /= 60;
	*tp++ = d1;

	/*
	 * day is the day number.
	 * generate day of the week.
	 * The addend is 4 mod 7 (1/1/1970 was Thursday)
	 */

	xtime.tm_wday = (day+7340036)%7;

	/*
	 * year number
	 */
	if (day>=0) for(d1=70; day >= dysize(d1); d1++)
		day -= dysize(d1);
	else for (d1=70; day<0; d1--)
		day += dysize(d1-1);
	xtime.tm_year = d1;
	xtime.tm_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;
	*tp++ = d0+1;
	*tp++ = d1;
	xtime.tm_isdst = 0;
	return(&xtime);
}

char *
asctime(t)
struct tm *t;
{
	register char *cp, *ncp;
	register int *tp;

	cp = cbuf;
	for (ncp = "Day Mon 00 00:00:00 1900\n"; *cp++ = *ncp++;);
	ncp = &"SunMonTueWedThuFriSat"[3*t->tm_wday];
	cp = cbuf;
	*cp++ = *ncp++;
	*cp++ = *ncp++;
	*cp++ = *ncp++;
	cp++;
	tp = &t->tm_mon;
	ncp = &"JanFebMarAprMayJunJulAugSepOctNovDec"[(*tp)*3];
	*cp++ = *ncp++;
	*cp++ = *ncp++;
	*cp++ = *ncp++;
	cp = ct_numb(cp, *--tp);
	cp = ct_numb(cp, *--tp+100);
	cp = ct_numb(cp, *--tp+100);
	cp = ct_numb(cp, *--tp+100);
	if (t->tm_year>=100) {
		cp[1] = '2';
		cp[2] = '0';
	}
	cp += 2;
	cp = ct_numb(cp, t->tm_year+100);
	return(cbuf);
}

dysize(y)
{
	if((y%4) == 0)
		return(366);
	return(365);
}

static char *
ct_numb(cp, n)
register char *cp;
{
	cp++;
	if (n>=10)
		*cp++ = (n/10)%10 + '0';
	else
		*cp++ = ' ';
	*cp++ = n%10 + '0';
	return(cp);
}
