nativelibc/time/datetime.c

/*	A part of the Native C Library for Windows NT
	Copyright 2026 Rivoreo

	This program is free software; you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation; either version 2 of the License, or (at
	your option) any later version.

	This program is distributed in the hope that it will be useful, but
	WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
	General Public License for more details.
*/

/*
 * A part of this file comes from public domain source, so
 * clarified as of June 5, 1996 by Arthur David Olson.
 */

#include <sys/types.h>
#include <stdint.h>
#include <limits.h>
#include <time.h>
#include <errno.h>
#include <float.h>

#define PCTS

#ifndef TYPE_BIT
#define TYPE_BIT(T) (sizeof(T) * CHAR_BIT)
#endif

#ifndef TYPE_SIGNED
#define TYPE_SIGNED(T) (((T)-1) < 0)
#endif

#ifndef TYPE_INTEGRAL
#define TYPE_INTEGRAL(T) (((T)0.5) != 0.5)
#endif

#ifndef YEARSPERREPEAT
#define YEARSPERREPEAT 400
#endif

#ifndef AVGSECSPERYEAR
#define AVGSECSPERYEAR 31556952L
#endif

#ifndef TZ_MAX_TIMES
#define TZ_MAX_TIMES 1200
#endif

#ifndef TZ_MAX_TYPES
#define TZ_MAX_TYPES 256 /* UINT8_MAX + 1 */
#endif

#ifndef TZ_MAX_CHARS
#define TZ_MAX_CHARS 50
#endif

#ifndef TZ_MAX_LEAPS
#define TZ_MAX_LEAPS 50
#endif

#define SECSPERMIN 60
#define MINSPERHOUR 60
#define HOURSPERDAY 24
#define DAYSPERWEEK 7
#define DAYSPERNYEAR 365
#define DAYSPERLYEAR 366
#define SECSPERHOUR (SECSPERMIN * MINSPERHOUR)
#define SECSPERDAY ((long int)SECSPERHOUR * HOURSPERDAY)
#define MONSPERYEAR 12

#define TM_SUNDAY 0
#define TM_MONDAY 1
#define TM_TUESDAY 2
#define TM_WEDNESDAY 3
#define TM_THURSDAY 4
#define TM_FRIDAY 5
#define TM_SATURDAY 6
#define TM_JANUARY 0
#define TM_FEBRUARY 1
#define TM_MARCH 2
#define TM_APRIL 3
#define TM_MAY 4
#define TM_JUNE 5
#define TM_JULY 6
#define TM_AUGUST 7
#define TM_SEPTEMBER 8
#define TM_OCTOBER 9
#define TM_NOVEMBER 10
#define TM_DECEMBER 11
#define TM_YEAR_BASE 1900

#define EPOCH_YEAR 1970
#define EPOCH_WDAY TM_THURSDAY

#define isleap(y) (((y) % 4) == 0 && (((y) % 100) != 0 || ((y) % 400) == 0))


#define _RWLOCK_RDLOCK(L)
#define _RWLOCK_UNLOCK(L)


#define GMT "UTC"

struct ttinfo {				/* time type information */
	long		tt_gmtoff;	/* UTC offset in seconds */
	int		tt_isdst;	/* used to set tm_isdst */
	int		tt_abbrind;	/* abbreviation list index */
	int		tt_ttisstd;	/* TRUE if transition is std time */
	int		tt_ttisgmt;	/* TRUE if transition is UTC */
};

struct lsinfo {				/* leap second information */
	time_t		ls_trans;	/* transition time */
	long		ls_corr;	/* correction to apply */
};

#define BIGGEST(a, b)	(((a) > (b)) ? (a) : (b))

#ifdef TZNAME_MAX
#define MY_TZNAME_MAX	TZNAME_MAX
#endif /* defined TZNAME_MAX */
#ifndef TZNAME_MAX
#define MY_TZNAME_MAX	255
#endif /* !defined TZNAME_MAX */

struct state {
	int		leapcnt;
	int		timecnt;
	int		typecnt;
	int		charcnt;
	int		goback;
	int		goahead;
	time_t		ats[TZ_MAX_TIMES];
	unsigned char	types[TZ_MAX_TIMES];
	struct ttinfo	ttis[TZ_MAX_TYPES];
	char		chars[BIGGEST(BIGGEST(TZ_MAX_CHARS + 1, sizeof GMT),
				(2 * (MY_TZNAME_MAX + 1)))];
	struct lsinfo	lsis[TZ_MAX_LEAPS];
};

static struct tm *	gmtsub(const time_t *, long int, struct tm *);
static struct tm *	localsub(const time_t *, long int, struct tm *);

#ifdef ALL_STATE
static struct state *	lclptr;
static struct state *	gmtptr;
#else
static struct state	lclmem;
static struct state	gmtmem;
#define lclptr		(&lclmem)
#define gmtptr		(&gmtmem)
#endif

static const int	mon_lengths[2][MONSPERYEAR] = {
	{ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
	{ 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
};

static const int	year_lengths[2] = {
	DAYSPERNYEAR, DAYSPERLYEAR
};

/*
** Adapted from code provided by Robert Elz, who writes:
**	The "best" way to do mktime I think is based on an idea of Bob
**	Kridle's (so its said...) from a long time ago.
**	It does a binary search of the time_t space. Since time_t's are
**	just 32 bits, its a max of 32 iterations (even at 64 bits it
**	would still be very reasonable).
*/

#ifndef WRONG
#define WRONG	(-1)
#endif

/*
** Simplified normalize logic courtesy Paul Eggert.
*/
static int increment_overflow(int *number, int delta)
{
	int number0 = *number;
	*number += delta;
	return (*number < number0) != (delta < 0);
}

static int normalize_overflow(int *const tensptr, int *const unitsptr, const int base)
{
	int tensdelta = (*unitsptr >= 0) ?
		(*unitsptr / base) :
		(-1 - (-1 - *unitsptr) / base);
	*unitsptr -= tensdelta * base;
	return increment_overflow(tensptr, tensdelta);
}

static int tmcomp(const struct tm *a, const struct tm *b)
{
	int diff = a->tm_year - b->tm_year;
	if(diff) return diff;
	diff = a->tm_mon - b->tm_mon;
	if(diff) return diff;
	diff = a->tm_mday - b->tm_mday;
	if(diff) return diff;
	diff = a->tm_hour - b->tm_hour;
	if(diff) return diff;
	diff = a->tm_min - b->tm_min;
	if(diff) return diff;
	return a->tm_sec - b->tm_sec;
}

static time_t time2sub(struct tm *const tmp, struct tm *(*const funcp)(const time_t *, long, struct tm *), const long int offset, int *const okayp, const int do_norm_secs)
{
	const struct state *	sp;
	int			dir;
	int			i, j;
	int			saved_seconds;
	int			li;
	time_t			lo;
	time_t			hi;
	int			y;
	time_t			newt;
	time_t			t;
	struct tm		yourtm, mytm;

	*okayp = 0;
	yourtm = *tmp;
	if (do_norm_secs) {
		if (normalize_overflow(&yourtm.tm_min, &yourtm.tm_sec,
			SECSPERMIN))
				return WRONG;
	}
	if (normalize_overflow(&yourtm.tm_hour, &yourtm.tm_min, MINSPERHOUR))
		return WRONG;
	if (normalize_overflow(&yourtm.tm_mday, &yourtm.tm_hour, HOURSPERDAY))
		return WRONG;
	y = yourtm.tm_year;
	if (normalize_overflow(&y, &yourtm.tm_mon, MONSPERYEAR)) return WRONG;
	/*
	** Turn y into an actual year number for now.
	** It is converted back to an offset from TM_YEAR_BASE later.
	*/
	if (increment_overflow(&y, TM_YEAR_BASE)) return WRONG;
	while (yourtm.tm_mday <= 0) {
		if (increment_overflow(&y, -1)) return WRONG;
		li = y + (1 < yourtm.tm_mon);
		yourtm.tm_mday += year_lengths[isleap(li)];
	}
	while (yourtm.tm_mday > DAYSPERLYEAR) {
		li = y + (1 < yourtm.tm_mon);
		yourtm.tm_mday -= year_lengths[isleap(li)];
		if (increment_overflow(&y, 1)) return WRONG;
	}
	for ( ; ; ) {
		i = mon_lengths[isleap(y)][yourtm.tm_mon];
		if (yourtm.tm_mday <= i)
			break;
		yourtm.tm_mday -= i;
		if (++yourtm.tm_mon >= MONSPERYEAR) {
			yourtm.tm_mon = 0;
			if (increment_overflow(&y, 1)) return WRONG;
		}
	}
	if (increment_overflow(&y, -TM_YEAR_BASE)) return WRONG;
	yourtm.tm_year = y;
	if (yourtm.tm_year != y)
		return WRONG;
	/* Don't go below 1900 for POLA */
	if (yourtm.tm_year < 0)
		return WRONG;
	if (yourtm.tm_sec >= 0 && yourtm.tm_sec < SECSPERMIN)
		saved_seconds = 0;
	else if (y + TM_YEAR_BASE < EPOCH_YEAR) {
		/*
		** We can't set tm_sec to 0, because that might push the
		** time below the minimum representable time.
		** Set tm_sec to 59 instead.
		** This assumes that the minimum representable time is
		** not in the same minute that a leap second was deleted from,
		** which is a safer assumption than using 58 would be.
		*/
		if (increment_overflow(&yourtm.tm_sec, 1 - SECSPERMIN))
			return WRONG;
		saved_seconds = yourtm.tm_sec;
		yourtm.tm_sec = SECSPERMIN - 1;
	} else {
		saved_seconds = yourtm.tm_sec;
		yourtm.tm_sec = 0;
	}
	/*
	** Do a binary search (this works whatever time_t's type is).
	*/
	if (!TYPE_SIGNED(time_t)) {
		lo = 0;
		hi = lo - 1;
	} else if (!TYPE_INTEGRAL(time_t)) {
		if (sizeof(time_t) > sizeof(float))
			hi = (time_t) DBL_MAX;
		else	hi = (time_t) FLT_MAX;
		lo = -hi;
	} else {
		lo = 1;
		for (i = 0; i < (int) TYPE_BIT(time_t) - 1; ++i)
			lo *= 2;
		hi = -(lo + 1);
	}
	for ( ; ; ) {
		t = lo / 2 + hi / 2;
		if (t < lo)
			t = lo;
		else if (t > hi)
			t = hi;
		if (!funcp(&t, offset, &mytm)) {
			/*
			** Assume that t is too extreme to be represented in
			** a struct tm; arrange things so that it is less
			** extreme on the next pass.
			*/
			dir = (t > 0) ? 1 : -1;
		} else	dir = tmcomp(&mytm, &yourtm);
		if (dir != 0) {
			if (t == lo) {
				++t;
				if (t <= lo)
					return WRONG;
				++lo;
			} else if (t == hi) {
				--t;
				if (t >= hi)
					return WRONG;
				--hi;
			}
			if (lo > hi)
				return WRONG;
			if (dir > 0)
				hi = t;
			else	lo = t;
			continue;
		}
		if (yourtm.tm_isdst < 0 || mytm.tm_isdst == yourtm.tm_isdst)
			break;
		/*
		** Right time, wrong type.
		** Hunt for right time, right type.
		** It's okay to guess wrong since the guess
		** gets checked.
		*/
		sp = (const struct state *)
			((funcp == localsub) ? lclptr : gmtptr);
#ifdef ALL_STATE
		if (sp == NULL)
			return WRONG;
#endif /* defined ALL_STATE */
		for (i = sp->typecnt - 1; i >= 0; --i) {
			if (sp->ttis[i].tt_isdst != yourtm.tm_isdst)
				continue;
			for (j = sp->typecnt - 1; j >= 0; --j) {
				if (sp->ttis[j].tt_isdst == yourtm.tm_isdst)
					continue;
				newt = t + sp->ttis[j].tt_gmtoff -
					sp->ttis[i].tt_gmtoff;
				if (!funcp(&newt, offset, &mytm)) continue;
				if (tmcomp(&mytm, &yourtm) != 0)
					continue;
				if (mytm.tm_isdst != yourtm.tm_isdst)
					continue;
				/*
				** We have a match.
				*/
				t = newt;
				goto label;
			}
		}
		return WRONG;
	}
label:
	newt = t + saved_seconds;
	if ((newt < t) != (saved_seconds < 0))
		return WRONG;
	t = newt;
	if (funcp(&t, offset, tmp)) *okayp = 1;
	return t;
}

static time_t time2(struct tm *const tmp, struct tm *(*const funcp)(const time_t *, long, struct tm *), const long offset, int *const okayp)
{
	/*
	** First try without normalization of seconds
	** (in case tm_sec contains a value associated with a leap second).
	** If that fails, try with normalization of seconds.
	*/
	time_t t = time2sub(tmp, funcp, offset, okayp, 0);
	if(*okayp) return t;
	return time2sub(tmp, funcp, offset, okayp, 1);
}

/*
** Return the number of leap years through the end of the given year
** where, to make the math easy, the answer for year zero is defined as zero.
*/
static int leaps_thru_end_of(const int y)
{
	return (y >= 0) ? (y / 4 - y / 100 + y / 400) :
		-(leaps_thru_end_of(-(y + 1)) + 1);
}

static struct tm *timesub(const time_t *const timep, const long int offset, const struct state *const sp, struct tm *const tmp)
{
	const struct lsinfo *	lp;
	time_t			tdays;
	int			idays;	/* unsigned would be so 2003 */
	long			rem;
	int			y;
	const int *		ip;
	long			corr;
	int			hit;
	int			i;

	corr = 0;
	hit = 0;
#ifdef ALL_STATE
	i = (sp == NULL) ? 0 : sp->leapcnt;
#else
	i = sp->leapcnt;
#endif
	while (--i >= 0) {
		lp = &sp->lsis[i];
		if (*timep >= lp->ls_trans) {
			if (*timep == lp->ls_trans) {
				hit = ((i == 0 && lp->ls_corr > 0) ||
					lp->ls_corr > sp->lsis[i - 1].ls_corr);
				if (hit)
					while (i > 0 &&
						sp->lsis[i].ls_trans ==
						sp->lsis[i - 1].ls_trans + 1 &&
						sp->lsis[i].ls_corr ==
						sp->lsis[i - 1].ls_corr + 1) {
							++hit;
							--i;
					}
			}
			corr = lp->ls_corr;
			break;
		}
	}
	y = EPOCH_YEAR;
	tdays = *timep / SECSPERDAY;
	rem = *timep - tdays * SECSPERDAY;
	while (tdays < 0 || tdays >= year_lengths[isleap(y)]) {
		int		newy;
		register time_t	tdelta;
		register int	idelta;
		register int	leapdays;

		tdelta = tdays / DAYSPERLYEAR;
		idelta = tdelta;
		if (tdelta - idelta >= 1 || idelta - tdelta >= 1)
			return NULL;
		if (idelta == 0)
			idelta = (tdays < 0) ? -1 : 1;
		newy = y;
		if (increment_overflow(&newy, idelta))
			return NULL;
		leapdays = leaps_thru_end_of(newy - 1) -
			leaps_thru_end_of(y - 1);
		tdays -= ((time_t) newy - y) * DAYSPERNYEAR;
		tdays -= leapdays;
		y = newy;
	}
	{
		register long	seconds;

		seconds = tdays * SECSPERDAY + 0.5;
		tdays = seconds / SECSPERDAY;
		rem += seconds - tdays * SECSPERDAY;
	}
	/*
	** Given the range, we can now fearlessly cast...
	*/
	idays = tdays;
	rem += offset - corr;
	while (rem < 0) {
		rem += SECSPERDAY;
		--idays;
	}
	while (rem >= SECSPERDAY) {
		rem -= SECSPERDAY;
		++idays;
	}
	while (idays < 0) {
		if (increment_overflow(&y, -1))
			return NULL;
		idays += year_lengths[isleap(y)];
	}
	while (idays >= year_lengths[isleap(y)]) {
		idays -= year_lengths[isleap(y)];
		if (increment_overflow(&y, 1))
			return NULL;
	}
	tmp->tm_year = y;
	if (increment_overflow(&tmp->tm_year, -TM_YEAR_BASE))
		return NULL;
	tmp->tm_yday = idays;
	/*
	** The "extra" mods below avoid overflow problems.
	*/
	tmp->tm_wday = EPOCH_WDAY +
		((y - EPOCH_YEAR) % DAYSPERWEEK) *
		(DAYSPERNYEAR % DAYSPERWEEK) +
		leaps_thru_end_of(y - 1) -
		leaps_thru_end_of(EPOCH_YEAR - 1) +
		idays;
	tmp->tm_wday %= DAYSPERWEEK;
	if (tmp->tm_wday < 0)
		tmp->tm_wday += DAYSPERWEEK;
	tmp->tm_hour = (int) (rem / SECSPERHOUR);
	rem %= SECSPERHOUR;
	tmp->tm_min = (int) (rem / SECSPERMIN);
	/*
	** A positive leap second requires a special
	** representation. This uses "... ??:59:60" et seq.
	*/
	tmp->tm_sec = (int) (rem % SECSPERMIN) + hit;
	ip = mon_lengths[isleap(y)];
	for (tmp->tm_mon = 0; idays >= ip[tmp->tm_mon]; ++(tmp->tm_mon))
		idays -= ip[tmp->tm_mon];
	tmp->tm_mday = (int) (idays + 1);
	tmp->tm_isdst = 0;
	return tmp;
}

/*
** The easy way to behave "as if no library function calls" localtime
** is to not call it--so we drop its guts into "localsub", which can be
** freely called. (And no, the PANS doesn't require the above behavior--
** but it *is* desirable.)
**
** The unused offset argument is for the benefit of mktime variants.
*/
/*ARGSUSED*/
static struct tm *localsub(const time_t *const timep, const long offset, struct tm *const tmp)
{
	struct state *		sp;
	const struct ttinfo *	ttisp;
	int			i;
	struct tm *		result;
	const time_t		t = *timep;

	sp = lclptr;
#ifdef ALL_STATE
	if (sp == NULL)
		return gmtsub(timep, offset, tmp);
#endif /* defined ALL_STATE */
	if ((sp->goback && t < sp->ats[0]) ||
		(sp->goahead && t > sp->ats[sp->timecnt - 1])) {
			time_t			newt = t;
			register time_t		seconds;
			register time_t		tcycles;
			register int_fast64_t	icycles;

			if (t < sp->ats[0])
				seconds = sp->ats[0] - t;
			else	seconds = t - sp->ats[sp->timecnt - 1];
			--seconds;
			tcycles = seconds / YEARSPERREPEAT / AVGSECSPERYEAR;
			++tcycles;
			icycles = tcycles;
			if (tcycles - icycles >= 1 || icycles - tcycles >= 1)
				return NULL;
			seconds = icycles;
			seconds *= YEARSPERREPEAT;
			seconds *= AVGSECSPERYEAR;
			if (t < sp->ats[0])
				newt += seconds;
			else	newt -= seconds;
			if (newt < sp->ats[0] ||
				newt > sp->ats[sp->timecnt - 1])
					return NULL;	/* "cannot happen" */
			result = localsub(&newt, offset, tmp);
			if (result == tmp) {
				register time_t	newy;

				newy = tmp->tm_year;
				if (t < sp->ats[0])
					newy -= icycles * YEARSPERREPEAT;
				else	newy += icycles * YEARSPERREPEAT;
				tmp->tm_year = newy;
				if (tmp->tm_year != newy)
					return NULL;
			}
			return result;
	}
	if (sp->timecnt == 0 || t < sp->ats[0]) {
		i = 0;
		while (sp->ttis[i].tt_isdst)
			if (++i >= sp->typecnt) {
				i = 0;
				break;
			}
	} else {
		register int	lo = 1;
		register int	hi = sp->timecnt;

		while (lo < hi) {
			register int	mid = (lo + hi) >> 1;

			if (t < sp->ats[mid])
				hi = mid;
			else	lo = mid + 1;
		}
		i = (int) sp->types[lo - 1];
	}
	ttisp = &sp->ttis[i];
	/*
	** To get (wrong) behavior that's compatible with System V Release 2.0
	** you'd replace the statement below with
	**	t += ttisp->tt_gmtoff;
	**	timesub(&t, 0L, sp, tmp);
	*/
	result = timesub(&t, ttisp->tt_gmtoff, sp, tmp);
	tmp->tm_isdst = ttisp->tt_isdst;
	tzname[tmp->tm_isdst] = &sp->chars[ttisp->tt_abbrind];
	return result;
}

/*
** gmtsub is to gmtime as localsub is to localtime.
*/
static struct tm *gmtsub(const time_t *const timep, const long int offset, struct tm *const tmp)
{
	return timesub(timep, offset, gmtptr, tmp);
}

static time_t time1(struct tm *const tmp, struct tm *(*const funcp)(const time_t *, long, struct tm *), const long int offset)
{
	time_t			t;
	const struct state *	sp;
	int			samei, otheri;
	int			sameind, otherind;
	int			i;
	int			nseen;
	int			seen[TZ_MAX_TYPES];
	int			types[TZ_MAX_TYPES];
	int			okay;

	if (tmp == NULL) {
		errno = EINVAL;
		return WRONG;
	}

	if (tmp->tm_isdst > 1)
		tmp->tm_isdst = 1;
	t = time2(tmp, funcp, offset, &okay);
#ifdef PCTS
	/*
	** PCTS code courtesy Grant Sullivan.
	*/
	if (okay)
		return t;
	if (tmp->tm_isdst < 0)
		tmp->tm_isdst = 0;	/* reset to std and try again */
#else
	if (okay || tmp->tm_isdst < 0)
		return t;
#endif /* !defined PCTS */
	/*
	** We're supposed to assume that somebody took a time of one type
	** and did some math on it that yielded a "struct tm" that's bad.
	** We try to divine the type they started from and adjust to the
	** type they need.
	*/
	sp = (const struct state *) ((funcp == localsub) ? lclptr : gmtptr);
#ifdef ALL_STATE
	if (sp == NULL)
		return WRONG;
#endif /* defined ALL_STATE */
	for (i = 0; i < sp->typecnt; ++i) seen[i] = 0;
	nseen = 0;
	for (i = sp->timecnt - 1; i >= 0; --i) {
		if (!seen[sp->types[i]]) {
			seen[sp->types[i]] = 1;
			types[nseen++] = sp->types[i];
		}
	}
	for (sameind = 0; sameind < nseen; ++sameind) {
		samei = types[sameind];
		if (sp->ttis[samei].tt_isdst != tmp->tm_isdst)
			continue;
		for (otherind = 0; otherind < nseen; ++otherind) {
			otheri = types[otherind];
			if (sp->ttis[otheri].tt_isdst == tmp->tm_isdst)
				continue;
			tmp->tm_sec += sp->ttis[otheri].tt_gmtoff -
					sp->ttis[samei].tt_gmtoff;
			tmp->tm_isdst = !tmp->tm_isdst;
			t = time2(tmp, funcp, offset, &okay);
			if (okay)
				return t;
			tmp->tm_sec -= sp->ttis[otheri].tt_gmtoff -
					sp->ttis[samei].tt_gmtoff;
			tmp->tm_isdst = !tmp->tm_isdst;
		}
	}
	return WRONG;
}

time_t
mktime(struct tm *const tmp)
{
	time_t mktime_return_value;
	_RWLOCK_RDLOCK(&lcl_rwlock);
	tzset();
	mktime_return_value = time1(tmp, localsub, 0L);
	_RWLOCK_UNLOCK(&lcl_rwlock);
	return(mktime_return_value);
}

time_t
timelocal(struct tm *const tmp)
{
	if (tmp != NULL)
		tmp->tm_isdst = -1;	/* in case it wasn't initialized */
	return mktime(tmp);
}

time_t
timegm(struct tm *const tmp)
{
	if (tmp != NULL)
		tmp->tm_isdst = 0;
	return time1(tmp, gmtsub, 0L);
}