/*
 * This file is in the public domain, so clarified as of
 * 1996-06-05 by Arthur David Olson.
 *
 * IDENTIFICATION
 *	  src/timezone/localtime.c
 */

/*
 * Leap second handling from Bradley White.
 * POSIX-style TZ environment variable handling from Guy Harris.
 */

/* this file needs to build in both frontend and backend contexts */
#include "c.h"

#include <fcntl.h>

#include "datatype/timestamp.h"
#include "private.h"
#include "pgtz.h"
#include "tzfile.h"


#ifndef WILDABBR
/*----------
 * Someone might make incorrect use of a time zone abbreviation:
 *	1.	They might reference tzname[0] before calling tzset (explicitly
 *		or implicitly).
 *	2.	They might reference tzname[1] before calling tzset (explicitly
 *		or implicitly).
 *	3.	They might reference tzname[1] after setting to a time zone
 *		in which Daylight Saving Time is never observed.
 *	4.	They might reference tzname[0] after setting to a time zone
 *		in which Standard Time is never observed.
 *	5.	They might reference tm.TM_ZONE after calling offtime.
 * What's best to do in the above cases is open to debate;
 * for now, we just set things up so that in any of the five cases
 * WILDABBR is used. Another possibility:	initialize tzname[0] to the
 * string "tzname[0] used before set", and similarly for the other cases.
 * And another: initialize tzname[0] to "ERA", with an explanation in the
 * manual page of what this "time zone abbreviation" means (doing this so
 * that tzname[0] has the "normal" length of three characters).
 *----------
 */
#define WILDABBR	"   "
#endif   /* !defined WILDABBR */

static char wildabbr[] = WILDABBR;

static const char gmt[] = "GMT";

/*
 * The DST rules to use if TZ has no rules and we can't load TZDEFRULES.
 * We default to US rules as of 1999-08-17.
 * POSIX 1003.1 section 8.1.1 says that the default DST rules are
 * implementation dependent; for historical reasons, US rules are a
 * common default.
 */
#define TZDEFRULESTRING ",M4.1.0,M10.5.0"

struct rule
{
	int			r_type;			/* type of rule--see below */
	int			r_day;			/* day number of rule */
	int			r_week;			/* week number of rule */
	int			r_mon;			/* month number of rule */
	long		r_time;			/* transition time of rule */
};

#define JULIAN_DAY		0		/* Jn - Julian day */
#define DAY_OF_YEAR		1		/* n - day of year */
#define MONTH_NTH_DAY_OF_WEEK	2		/* Mm.n.d - month, week, day of week */

/*
 * Prototypes for static functions.
 */

static long detzcode(const char *codep);
static pg_time_t detzcode64(const char *codep);
static int	differ_by_repeat(pg_time_t t1, pg_time_t t0);
static const char *getzname(const char *strp);
static const char *getqzname(const char *strp, int delim);
static const char *getnum(const char *strp, int *nump, int min, int max);
static const char *getsecs(const char *strp, long *secsp);
static const char *getoffset(const char *strp, long *offsetp);
static const char *getrule(const char *strp, struct rule * rulep);
static void gmtload(struct state * sp);
static struct pg_tm *gmtsub(const pg_time_t *timep, long offset,
	   struct pg_tm * tmp);
static struct pg_tm *localsub(const pg_time_t *timep, long offset,
		 struct pg_tm * tmp, const pg_tz *tz);
static int	increment_overflow(int *number, int delta);
static pg_time_t transtime(pg_time_t janfirst, int year,
		  const struct rule * rulep, long offset);
static int	typesequiv(const struct state * sp, int a, int b);
static struct pg_tm *timesub(const pg_time_t *timep, long offset,
		const struct state * sp, struct pg_tm * tmp);

/* GMT timezone */
static struct state gmtmem;

#define gmtptr		(&gmtmem)


static int	gmt_is_set = 0;

/*
 * Section 4.12.3 of X3.159-1989 requires that
 *	Except for the strftime function, these functions [asctime,
 *	ctime, gmtime, localtime] return values in one of two static
 *	objects: a broken-down time structure and an array of char.
 * Thanks to Paul Eggert for noting this.
 */

static struct pg_tm tm;


static long
detzcode(const char *codep)
{
	long		result;
	int			i;

	result = (codep[0] & 0x80) ? ~0L : 0;
	for (i = 0; i < 4; ++i)
		result = (result << 8) | (codep[i] & 0xff);
	return result;
}

static pg_time_t
detzcode64(const char *codep)
{
	pg_time_t	result;
	int			i;

	result = (codep[0] & 0x80) ? (~(int64) 0) : 0;
	for (i = 0; i < 8; ++i)
		result = result * 256 + (codep[i] & 0xff);
	return result;
}

static int
differ_by_repeat(pg_time_t t1, pg_time_t t0)
{
	if (TYPE_INTEGRAL(pg_time_t) &&
		TYPE_BIT(pg_time_t) -TYPE_SIGNED(pg_time_t) <SECSPERREPEAT_BITS)
		return 0;
	return t1 - t0 == SECSPERREPEAT;
}

int
tzload(const char *name, char *canonname, struct state * sp, int doextend)
{
	const char *p;
	int			i;
	int			fid;
	int			stored;
	int			nread;
	union
	{
		struct tzhead tzhead;
		char		buf[2 * sizeof(struct tzhead) +
									2 * sizeof *sp +
									4 * TZ_MAX_TIMES];
	}			u;

	sp->goback = sp->goahead = FALSE;
	if (name == NULL && (name = TZDEFAULT) == NULL)
		return -1;
	if (name[0] == ':')
		++name;
	fid = pg_open_tzfile(name, canonname);
	if (fid < 0)
		return -1;
	nread = read(fid, u.buf, sizeof u.buf);
	if (close(fid) != 0 || nread <= 0)
		return -1;
	for (stored = 4; stored <= 8; stored *= 2)
	{
		int			ttisstdcnt;
		int			ttisgmtcnt;

		ttisstdcnt = (int) detzcode(u.tzhead.tzh_ttisstdcnt);
		ttisgmtcnt = (int) detzcode(u.tzhead.tzh_ttisgmtcnt);
		sp->leapcnt = (int) detzcode(u.tzhead.tzh_leapcnt);
		sp->timecnt = (int) detzcode(u.tzhead.tzh_timecnt);
		sp->typecnt = (int) detzcode(u.tzhead.tzh_typecnt);
		sp->charcnt = (int) detzcode(u.tzhead.tzh_charcnt);
		p = u.tzhead.tzh_charcnt + sizeof u.tzhead.tzh_charcnt;
		if (sp->leapcnt < 0 || sp->leapcnt > TZ_MAX_LEAPS ||
			sp->typecnt <= 0 || sp->typecnt > TZ_MAX_TYPES ||
			sp->timecnt < 0 || sp->timecnt > TZ_MAX_TIMES ||
			sp->charcnt < 0 || sp->charcnt > TZ_MAX_CHARS ||
			(ttisstdcnt != sp->typecnt && ttisstdcnt != 0) ||
			(ttisgmtcnt != sp->typecnt && ttisgmtcnt != 0))
			return -1;
		if (nread - (p - u.buf) <
			sp->timecnt * stored +		/* ats */
			sp->timecnt +		/* types */
			sp->typecnt * 6 +	/* ttinfos */
			sp->charcnt +		/* chars */
			sp->leapcnt * (stored + 4) +		/* lsinfos */
			ttisstdcnt +		/* ttisstds */
			ttisgmtcnt)			/* ttisgmts */
			return -1;
		for (i = 0; i < sp->timecnt; ++i)
		{
			sp->ats[i] = (stored == 4) ? detzcode(p) : detzcode64(p);
			p += stored;
		}
		for (i = 0; i < sp->timecnt; ++i)
		{
			sp->types[i] = (unsigned char) *p++;
			if (sp->types[i] >= sp->typecnt)
				return -1;
		}
		for (i = 0; i < sp->typecnt; ++i)
		{
			struct ttinfo *ttisp;

			ttisp = &sp->ttis[i];
			ttisp->tt_gmtoff = detzcode(p);
			p += 4;
			ttisp->tt_isdst = (unsigned char) *p++;
			if (ttisp->tt_isdst != 0 && ttisp->tt_isdst != 1)
				return -1;
			ttisp->tt_abbrind = (unsigned char) *p++;
			if (ttisp->tt_abbrind < 0 ||
				ttisp->tt_abbrind > sp->charcnt)
				return -1;
		}
		for (i = 0; i < sp->charcnt; ++i)
			sp->chars[i] = *p++;
		sp->chars[i] = '\0';	/* ensure '\0' at end */
		for (i = 0; i < sp->leapcnt; ++i)
		{
			struct lsinfo *lsisp;

			lsisp = &sp->lsis[i];
			lsisp->ls_trans = (stored == 4) ? detzcode(p) : detzcode64(p);
			p += stored;
			lsisp->ls_corr = detzcode(p);
			p += 4;
		}
		for (i = 0; i < sp->typecnt; ++i)
		{
			struct ttinfo *ttisp;

			ttisp = &sp->ttis[i];
			if (ttisstdcnt == 0)
				ttisp->tt_ttisstd = FALSE;
			else
			{
				ttisp->tt_ttisstd = *p++;
				if (ttisp->tt_ttisstd != TRUE &&
					ttisp->tt_ttisstd != FALSE)
					return -1;
			}
		}
		for (i = 0; i < sp->typecnt; ++i)
		{
			struct ttinfo *ttisp;

			ttisp = &sp->ttis[i];
			if (ttisgmtcnt == 0)
				ttisp->tt_ttisgmt = FALSE;
			else
			{
				ttisp->tt_ttisgmt = *p++;
				if (ttisp->tt_ttisgmt != TRUE &&
					ttisp->tt_ttisgmt != FALSE)
					return -1;
			}
		}

		/*
		 * Out-of-sort ats should mean we're running on a signed time_t system
		 * but using a data file with unsigned values (or vice versa).
		 */
		for (i = 0; i < sp->timecnt - 2; ++i)
			if (sp->ats[i] > sp->ats[i + 1])
			{
				++i;
				if (TYPE_SIGNED(pg_time_t))
				{
					/*
					 * Ignore the end (easy).
					 */
					sp->timecnt = i;
				}
				else
				{
					/*
					 * Ignore the beginning (harder).
					 */
					int			j;

					for (j = 0; j + i < sp->timecnt; ++j)
					{
						sp->ats[j] = sp->ats[j + i];
						sp->types[j] = sp->types[j + i];
					}
					sp->timecnt = j;
				}
				break;
			}

		/*
		 * If this is an old file, we're done.
		 */
		if (u.tzhead.tzh_version[0] == '\0')
			break;
		nread -= p - u.buf;
		for (i = 0; i < nread; ++i)
			u.buf[i] = p[i];

		/*
		 * If this is a narrow integer time_t system, we're done.
		 */
		if (stored >= (int) sizeof(pg_time_t) && TYPE_INTEGRAL(pg_time_t))
			break;
	}
	if (doextend && nread > 2 &&
		u.buf[0] == '\n' && u.buf[nread - 1] == '\n' &&
		sp->typecnt + 2 <= TZ_MAX_TYPES)
	{
		struct state ts;
		int			result;

		u.buf[nread - 1] = '\0';
		result = tzparse(&u.buf[1], &ts, FALSE);
		if (result == 0 && ts.typecnt == 2 &&
			sp->charcnt + ts.charcnt <= TZ_MAX_CHARS)
		{
			for (i = 0; i < 2; ++i)
				ts.ttis[i].tt_abbrind +=
					sp->charcnt;
			for (i = 0; i < ts.charcnt; ++i)
				sp->chars[sp->charcnt++] =
					ts.chars[i];
			i = 0;
			while (i < ts.timecnt &&
				   ts.ats[i] <=
				   sp->ats[sp->timecnt - 1])
				++i;
			while (i < ts.timecnt &&
				   sp->timecnt < TZ_MAX_TIMES)
			{
				sp->ats[sp->timecnt] =
					ts.ats[i];
				sp->types[sp->timecnt] =
					sp->typecnt +
					ts.types[i];
				++sp->timecnt;
				++i;
			}
			sp->ttis[sp->typecnt++] = ts.ttis[0];
			sp->ttis[sp->typecnt++] = ts.ttis[1];
		}
	}
	if (sp->timecnt > 1)
	{
		for (i = 1; i < sp->timecnt; ++i)
			if (typesequiv(sp, sp->types[i], sp->types[0]) &&
				differ_by_repeat(sp->ats[i], sp->ats[0]))
			{
				sp->goback = TRUE;
				break;
			}
		for (i = sp->timecnt - 2; i >= 0; --i)
			if (typesequiv(sp, sp->types[sp->timecnt - 1],
						   sp->types[i]) &&
				differ_by_repeat(sp->ats[sp->timecnt - 1],
								 sp->ats[i]))
			{
				sp->goahead = TRUE;
				break;
			}
	}
	return 0;
}

static int
typesequiv(const struct state * sp, int a, int b)
{
	int			result;

	if (sp == NULL ||
		a < 0 || a >= sp->typecnt ||
		b < 0 || b >= sp->typecnt)
		result = FALSE;
	else
	{
		const struct ttinfo *ap = &sp->ttis[a];
		const struct ttinfo *bp = &sp->ttis[b];

		result = ap->tt_gmtoff == bp->tt_gmtoff &&
			ap->tt_isdst == bp->tt_isdst &&
			ap->tt_ttisstd == bp->tt_ttisstd &&
			ap->tt_ttisgmt == bp->tt_ttisgmt &&
			strcmp(&sp->chars[ap->tt_abbrind],
				   &sp->chars[bp->tt_abbrind]) == 0;
	}
	return result;
}

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
};

/*
 * Given a pointer into a time zone string, scan until a character that is not
 * a valid character in a zone name is found. Return a pointer to that
 * character.
 */
static const char *
getzname(const char *strp)
{
	char		c;

	while ((c = *strp) != '\0' && !is_digit(c) && c != ',' && c != '-' &&
		   c != '+')
		++strp;
	return strp;
}

/*
 * Given a pointer into an extended time zone string, scan until the ending
 * delimiter of the zone name is located. Return a pointer to the delimiter.
 *
 * As with getzname above, the legal character set is actually quite
 * restricted, with other characters producing undefined results.
 * We don't do any checking here; checking is done later in common-case code.
 */
static const char *
getqzname(const char *strp, int delim)
{
	int			c;

	while ((c = *strp) != '\0' && c != delim)
		++strp;
	return strp;
}

/*
 * Given a pointer into a time zone string, extract a number from that string.
 * Check that the number is within a specified range; if it is not, return
 * NULL.
 * Otherwise, return a pointer to the first character not part of the number.
 */
static const char *
getnum(const char *strp, int *nump, int min, int max)
{
	char		c;
	int			num;

	if (strp == NULL || !is_digit(c = *strp))
		return NULL;
	num = 0;
	do
	{
		num = num * 10 + (c - '0');
		if (num > max)
			return NULL;		/* illegal value */
		c = *++strp;
	} while (is_digit(c));
	if (num < min)
		return NULL;			/* illegal value */
	*nump = num;
	return strp;
}

/*
 * Given a pointer into a time zone string, extract a number of seconds,
 * in hh[:mm[:ss]] form, from the string.
 * If any error occurs, return NULL.
 * Otherwise, return a pointer to the first character not part of the number
 * of seconds.
 */
static const char *
getsecs(const char *strp, long *secsp)
{
	int			num;

	/*
	 * `HOURSPERDAY * DAYSPERWEEK - 1' allows quasi-Posix rules like
	 * "M10.4.6/26", which does not conform to Posix, but which specifies the
	 * equivalent of ``02:00 on the first Sunday on or after 23 Oct''.
	 */
	strp = getnum(strp, &num, 0, HOURSPERDAY * DAYSPERWEEK - 1);
	if (strp == NULL)
		return NULL;
	*secsp = num * (long) SECSPERHOUR;
	if (*strp == ':')
	{
		++strp;
		strp = getnum(strp, &num, 0, MINSPERHOUR - 1);
		if (strp == NULL)
			return NULL;
		*secsp += num * SECSPERMIN;
		if (*strp == ':')
		{
			++strp;
			/* `SECSPERMIN' allows for leap seconds. */
			strp = getnum(strp, &num, 0, SECSPERMIN);
			if (strp == NULL)
				return NULL;
			*secsp += num;
		}
	}
	return strp;
}

/*
 * Given a pointer into a time zone string, extract an offset, in
 * [+-]hh[:mm[:ss]] form, from the string.
 * If any error occurs, return NULL.
 * Otherwise, return a pointer to the first character not part of the time.
 */
static const char *
getoffset(const char *strp, long *offsetp)
{
	int			neg = 0;

	if (*strp == '-')
	{
		neg = 1;
		++strp;
	}
	else if (*strp == '+')
		++strp;
	strp = getsecs(strp, offsetp);
	if (strp == NULL)
		return NULL;			/* illegal time */
	if (neg)
		*offsetp = -*offsetp;
	return strp;
}

/*
 * Given a pointer into a time zone string, extract a rule in the form
 * date[/time]. See POSIX section 8 for the format of "date" and "time".
 * If a valid rule is not found, return NULL.
 * Otherwise, return a pointer to the first character not part of the rule.
 */
static const char *
getrule(const char *strp, struct rule * rulep)
{
	if (*strp == 'J')
	{
		/*
		 * Julian day.
		 */
		rulep->r_type = JULIAN_DAY;
		++strp;
		strp = getnum(strp, &rulep->r_day, 1, DAYSPERNYEAR);
	}
	else if (*strp == 'M')
	{
		/*
		 * Month, week, day.
		 */
		rulep->r_type = MONTH_NTH_DAY_OF_WEEK;
		++strp;
		strp = getnum(strp, &rulep->r_mon, 1, MONSPERYEAR);
		if (strp == NULL)
			return NULL;
		if (*strp++ != '.')
			return NULL;
		strp = getnum(strp, &rulep->r_week, 1, 5);
		if (strp == NULL)
			return NULL;
		if (*strp++ != '.')
			return NULL;
		strp = getnum(strp, &rulep->r_day, 0, DAYSPERWEEK - 1);
	}
	else if (is_digit(*strp))
	{
		/*
		 * Day of year.
		 */
		rulep->r_type = DAY_OF_YEAR;
		strp = getnum(strp, &rulep->r_day, 0, DAYSPERLYEAR - 1);
	}
	else
		return NULL;			/* invalid format */
	if (strp == NULL)
		return NULL;
	if (*strp == '/')
	{
		/*
		 * Time specified.
		 */
		++strp;
		strp = getsecs(strp, &rulep->r_time);
	}
	else
		rulep->r_time = 2 * SECSPERHOUR;		/* default = 2:00:00 */
	return strp;
}

/*
 * Given the Epoch-relative time of January 1, 00:00:00 UTC, in a year, the
 * year, a rule, and the offset from UTC at the time that rule takes effect,
 * calculate the Epoch-relative time that rule takes effect.
 */
static pg_time_t
transtime(pg_time_t janfirst, int year,
		  const struct rule * rulep, long offset)
{
	int			leapyear;
	pg_time_t	value = 0;
	int			i,
				d,
				m1,
				yy0,
				yy1,
				yy2,
				dow;

	leapyear = isleap(year);
	switch (rulep->r_type)
	{

		case JULIAN_DAY:

			/*
			 * Jn - Julian day, 1 == January 1, 60 == March 1 even in leap
			 * years. In non-leap years, or if the day number is 59 or less,
			 * just add SECSPERDAY times the day number-1 to the time of
			 * January 1, midnight, to get the day.
			 */
			value = janfirst + (rulep->r_day - 1) * SECSPERDAY;
			if (leapyear && rulep->r_day >= 60)
				value += SECSPERDAY;
			break;

		case DAY_OF_YEAR:

			/*
			 * n - day of year. Just add SECSPERDAY times the day number to
			 * the time of January 1, midnight, to get the day.
			 */
			value = janfirst + rulep->r_day * SECSPERDAY;
			break;

		case MONTH_NTH_DAY_OF_WEEK:

			/*
			 * Mm.n.d - nth "dth day" of month m.
			 */
			value = janfirst;
			for (i = 0; i < rulep->r_mon - 1; ++i)
				value += mon_lengths[leapyear][i] * SECSPERDAY;

			/*
			 * Use Zeller's Congruence to get day-of-week of first day of
			 * month.
			 */
			m1 = (rulep->r_mon + 9) % 12 + 1;
			yy0 = (rulep->r_mon <= 2) ? (year - 1) : year;
			yy1 = yy0 / 100;
			yy2 = yy0 % 100;
			dow = ((26 * m1 - 2) / 10 +
				   1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
			if (dow < 0)
				dow += DAYSPERWEEK;

			/*
			 * "dow" is the day-of-week of the first day of the month. Get the
			 * day-of-month (zero-origin) of the first "dow" day of the month.
			 */
			d = rulep->r_day - dow;
			if (d < 0)
				d += DAYSPERWEEK;
			for (i = 1; i < rulep->r_week; ++i)
			{
				if (d + DAYSPERWEEK >=
					mon_lengths[leapyear][rulep->r_mon - 1])
					break;
				d += DAYSPERWEEK;
			}

			/*
			 * "d" is the day-of-month (zero-origin) of the day we want.
			 */
			value += d * SECSPERDAY;
			break;
	}

	/*
	 * "value" is the Epoch-relative time of 00:00:00 UTC on the day in
	 * question.  To get the Epoch-relative time of the specified local time
	 * on that day, add the transition time and the current offset from UTC.
	 */
	return value + rulep->r_time + offset;
}

/*
 * Given a POSIX section 8-style TZ string, fill in the rule tables as
 * appropriate.
 */

int
tzparse(const char *name, struct state * sp, int lastditch)
{
	const char *stdname;
	const char *dstname = NULL;
	size_t		stdlen;
	size_t		dstlen;
	long		stdoffset;
	long		dstoffset;
	pg_time_t  *atp;
	unsigned char *typep;
	char	   *cp;
	int			load_result;

	stdname = name;
	if (lastditch)
	{
		stdlen = strlen(name);	/* length of standard zone name */
		name += stdlen;
		if (stdlen >= sizeof sp->chars)
			stdlen = (sizeof sp->chars) - 1;
		stdoffset = 0;

		/*
		 * Unlike the original zic library, do NOT invoke tzload() here; we
		 * can't assume pg_open_tzfile() is sane yet, and we don't care about
		 * leap seconds anyway.
		 */
		sp->goback = sp->goahead = FALSE;
		load_result = -1;
	}
	else
	{
		if (*name == '<')
		{
			name++;
			stdname = name;
			name = getqzname(name, '>');
			if (*name != '>')
				return (-1);
			stdlen = name - stdname;
			name++;
		}
		else
		{
			name = getzname(name);
			stdlen = name - stdname;
		}
		if (*name == '\0')
			return -1;
		name = getoffset(name, &stdoffset);
		if (name == NULL)
			return -1;
		load_result = tzload(TZDEFRULES, NULL, sp, FALSE);
	}
	if (load_result != 0)
		sp->leapcnt = 0;		/* so, we're off a little */
	if (*name != '\0')
	{
		if (*name == '<')
		{
			dstname = ++name;
			name = getqzname(name, '>');
			if (*name != '>')
				return -1;
			dstlen = name - dstname;
			name++;
		}
		else
		{
			dstname = name;
			name = getzname(name);
			dstlen = name - dstname;	/* length of DST zone name */
		}
		if (*name != '\0' && *name != ',' && *name != ';')
		{
			name = getoffset(name, &dstoffset);
			if (name == NULL)
				return -1;
		}
		else
			dstoffset = stdoffset - SECSPERHOUR;
		if (*name == '\0' && load_result != 0)
			name = TZDEFRULESTRING;
		if (*name == ',' || *name == ';')
		{
			struct rule start;
			struct rule end;
			int			year;
			pg_time_t	janfirst;
			pg_time_t	starttime;
			pg_time_t	endtime;

			++name;
			if ((name = getrule(name, &start)) == NULL)
				return -1;
			if (*name++ != ',')
				return -1;
			if ((name = getrule(name, &end)) == NULL)
				return -1;
			if (*name != '\0')
				return -1;
			sp->typecnt = 2;	/* standard time and DST */

			/*
			 * Two transitions per year, from EPOCH_YEAR forward.
			 */
			sp->ttis[0].tt_gmtoff = -dstoffset;
			sp->ttis[0].tt_isdst = 1;
			sp->ttis[0].tt_abbrind = stdlen + 1;
			sp->ttis[1].tt_gmtoff = -stdoffset;
			sp->ttis[1].tt_isdst = 0;
			sp->ttis[1].tt_abbrind = 0;
			atp = sp->ats;
			typep = sp->types;
			janfirst = 0;
			sp->timecnt = 0;
			for (year = EPOCH_YEAR;
				 sp->timecnt + 2 <= TZ_MAX_TIMES;
				 ++year)
			{
				pg_time_t	newfirst;

				starttime = transtime(janfirst, year, &start,
									  stdoffset);
				endtime = transtime(janfirst, year, &end,
									dstoffset);
				if (starttime > endtime)
				{
					*atp++ = endtime;
					*typep++ = 1;		/* DST ends */
					*atp++ = starttime;
					*typep++ = 0;		/* DST begins */
				}
				else
				{
					*atp++ = starttime;
					*typep++ = 0;		/* DST begins */
					*atp++ = endtime;
					*typep++ = 1;		/* DST ends */
				}
				sp->timecnt += 2;
				newfirst = janfirst;
				newfirst += year_lengths[isleap(year)] *
					SECSPERDAY;
				if (newfirst <= janfirst)
					break;
				janfirst = newfirst;
			}
		}
		else
		{
			long		theirstdoffset;
			long		theirdstoffset;
			long		theiroffset;
			int			isdst;
			int			i;
			int			j;

			if (*name != '\0')
				return -1;

			/*
			 * Initial values of theirstdoffset and theirdstoffset.
			 */
			theirstdoffset = 0;
			for (i = 0; i < sp->timecnt; ++i)
			{
				j = sp->types[i];
				if (!sp->ttis[j].tt_isdst)
				{
					theirstdoffset =
						-sp->ttis[j].tt_gmtoff;
					break;
				}
			}
			theirdstoffset = 0;
			for (i = 0; i < sp->timecnt; ++i)
			{
				j = sp->types[i];
				if (sp->ttis[j].tt_isdst)
				{
					theirdstoffset =
						-sp->ttis[j].tt_gmtoff;
					break;
				}
			}

			/*
			 * Initially we're assumed to be in standard time.
			 */
			isdst = FALSE;
			theiroffset = theirstdoffset;

			/*
			 * Now juggle transition times and types tracking offsets as you
			 * do.
			 */
			for (i = 0; i < sp->timecnt; ++i)
			{
				j = sp->types[i];
				sp->types[i] = sp->ttis[j].tt_isdst;
				if (sp->ttis[j].tt_ttisgmt)
				{
					/* No adjustment to transition time */
				}
				else
				{
					/*
					 * If summer time is in effect, and the transition time
					 * was not specified as standard time, add the summer time
					 * offset to the transition time; otherwise, add the
					 * standard time offset to the transition time.
					 */

					/*
					 * Transitions from DST to DDST will effectively disappear
					 * since POSIX provides for only one DST offset.
					 */
					if (isdst && !sp->ttis[j].tt_ttisstd)
					{
						sp->ats[i] += dstoffset -
							theirdstoffset;
					}
					else
					{
						sp->ats[i] += stdoffset -
							theirstdoffset;
					}
				}
				theiroffset = -sp->ttis[j].tt_gmtoff;
				if (sp->ttis[j].tt_isdst)
					theirdstoffset = theiroffset;
				else
					theirstdoffset = theiroffset;
			}

			/*
			 * Finally, fill in ttis. ttisstd and ttisgmt need not be handled.
			 */
			sp->ttis[0].tt_gmtoff = -stdoffset;
			sp->ttis[0].tt_isdst = FALSE;
			sp->ttis[0].tt_abbrind = 0;
			sp->ttis[1].tt_gmtoff = -dstoffset;
			sp->ttis[1].tt_isdst = TRUE;
			sp->ttis[1].tt_abbrind = stdlen + 1;
			sp->typecnt = 2;
		}
	}
	else
	{
		dstlen = 0;
		sp->typecnt = 1;		/* only standard time */
		sp->timecnt = 0;
		sp->ttis[0].tt_gmtoff = -stdoffset;
		sp->ttis[0].tt_isdst = 0;
		sp->ttis[0].tt_abbrind = 0;
	}
	sp->charcnt = stdlen + 1;
	if (dstlen != 0)
		sp->charcnt += dstlen + 1;
	if ((size_t) sp->charcnt > sizeof sp->chars)
		return -1;
	cp = sp->chars;
	(void) strncpy(cp, stdname, stdlen);
	cp += stdlen;
	*cp++ = '\0';
	if (dstlen != 0)
	{
		(void) strncpy(cp, dstname, dstlen);
		*(cp + dstlen) = '\0';
	}
	return 0;
}

static void
gmtload(struct state * sp)
{
	if (tzload(gmt, NULL, sp, TRUE) != 0)
		(void) tzparse(gmt, sp, TRUE);
}


/*
 * 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.
 */
static struct pg_tm *
localsub(const pg_time_t *timep, long offset,
		 struct pg_tm * tmp, const pg_tz *tz)
{
	const struct state *sp;
	const struct ttinfo *ttisp;
	int			i;
	struct pg_tm *result;
	const pg_time_t t = *timep;

	sp = &tz->state;
	if ((sp->goback && t < sp->ats[0]) ||
		(sp->goahead && t > sp->ats[sp->timecnt - 1]))
	{
		pg_time_t	newt = t;
		pg_time_t	seconds;
		pg_time_t	tcycles;
		int64		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, tz);
		if (result == tmp)
		{
			pg_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
	{
		int			lo = 1;
		int			hi = sp->timecnt;

		while (lo < hi)
		{
			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];

	result = timesub(&t, ttisp->tt_gmtoff, sp, tmp);
	tmp->tm_isdst = ttisp->tt_isdst;
	tmp->tm_zone = &sp->chars[ttisp->tt_abbrind];
	return result;
}


struct pg_tm *
pg_localtime(const pg_time_t *timep, const pg_tz *tz)
{
	return localsub(timep, 0L, &tm, tz);
}


/*
 * gmtsub is to gmtime as localsub is to localtime.
 */
static struct pg_tm *
gmtsub(const pg_time_t *timep, long offset, struct pg_tm * tmp)
{
	struct pg_tm *result;

	if (!gmt_is_set)
	{
		gmt_is_set = TRUE;
		gmtload(gmtptr);
	}
	result = timesub(timep, offset, gmtptr, tmp);

	/*
	 * Could get fancy here and deliver something such as "UTC+xxxx" or
	 * "UTC-xxxx" if offset is non-zero, but this is no time for a treasure
	 * hunt.
	 */
	if (offset != 0)
		tmp->tm_zone = wildabbr;
	else
		tmp->tm_zone = gmtptr->chars;

	return result;
}

struct pg_tm *
pg_gmtime(const pg_time_t *timep)
{
	return gmtsub(timep, 0L, &tm);
}

/*
 * 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 pg_tm *
timesub(const pg_time_t *timep, long offset,
		const struct state * sp, struct pg_tm * tmp)
{
	const struct lsinfo *lp;
	pg_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;
	i = sp->leapcnt;
	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;
		pg_time_t	tdelta;
		int			idelta;
		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 -= ((pg_time_t) newy - y) * DAYSPERNYEAR;
		tdays -= leapdays;
		y = newy;
	}
	{
		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;
	tmp->tm_gmtoff = offset;
	return tmp;
}

/*
 * Simplified normalize logic courtesy Paul Eggert.
 */

static int
increment_overflow(int *number, int delta)
{
	int			number0;

	number0 = *number;
	*number += delta;
	return (*number < number0) != (delta < 0);
}

/*
 * Find the next DST transition time at or after the given time
 *
 * *timep is the input value, the other parameters are output values.
 *
 * When the function result is 1, *boundary is set to the time_t
 * representation of the next DST transition time at or after *timep,
 * *before_gmtoff and *before_isdst are set to the GMT offset and isdst
 * state prevailing just before that boundary, and *after_gmtoff and
 * *after_isdst are set to the state prevailing just after that boundary.
 *
 * When the function result is 0, there is no known DST transition at or
 * after *timep, but *before_gmtoff and *before_isdst indicate the GMT
 * offset and isdst state prevailing at *timep.  (This would occur in
 * DST-less time zones, for example.)
 *
 * A function result of -1 indicates failure (this case does not actually
 * occur in our current implementation).
 */
int
pg_next_dst_boundary(const pg_time_t *timep,
					 long int *before_gmtoff,
					 int *before_isdst,
					 pg_time_t *boundary,
					 long int *after_gmtoff,
					 int *after_isdst,
					 const pg_tz *tz)
{
	const struct state *sp;
	const struct ttinfo *ttisp;
	int			i;
	int			j;
	const pg_time_t t = *timep;

	sp = &tz->state;
	if (sp->timecnt == 0)
	{
		/* non-DST zone, use lowest-numbered standard type */
		i = 0;
		while (sp->ttis[i].tt_isdst)
			if (++i >= sp->typecnt)
			{
				i = 0;
				break;
			}
		ttisp = &sp->ttis[i];
		*before_gmtoff = ttisp->tt_gmtoff;
		*before_isdst = ttisp->tt_isdst;
		return 0;
	}
	if ((sp->goback && t < sp->ats[0]) ||
		(sp->goahead && t > sp->ats[sp->timecnt - 1]))
	{
		/* For values outside the transition table, extrapolate */
		pg_time_t	newt = t;
		pg_time_t	seconds;
		pg_time_t	tcycles;
		int64		icycles;
		int			result;

		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 -1;
		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 -1;			/* "cannot happen" */

		result = pg_next_dst_boundary(&newt, before_gmtoff,
									  before_isdst,
									  boundary,
									  after_gmtoff,
									  after_isdst,
									  tz);
		if (t < sp->ats[0])
			*boundary -= seconds;
		else
			*boundary += seconds;
		return result;
	}

	if (t > sp->ats[sp->timecnt - 1])
	{
		/* No known transition >= t, so use last known segment's type */
		i = sp->types[sp->timecnt - 1];
		ttisp = &sp->ttis[i];
		*before_gmtoff = ttisp->tt_gmtoff;
		*before_isdst = ttisp->tt_isdst;
		return 0;
	}
	if (t <= sp->ats[0])
	{
		/* For "before", use lowest-numbered standard type */
		i = 0;
		while (sp->ttis[i].tt_isdst)
			if (++i >= sp->typecnt)
			{
				i = 0;
				break;
			}
		ttisp = &sp->ttis[i];
		*before_gmtoff = ttisp->tt_gmtoff;
		*before_isdst = ttisp->tt_isdst;
		*boundary = sp->ats[0];
		/* And for "after", use the first segment's type */
		i = sp->types[0];
		ttisp = &sp->ttis[i];
		*after_gmtoff = ttisp->tt_gmtoff;
		*after_isdst = ttisp->tt_isdst;
		return 1;
	}
	/* Else search to find the containing segment */
	{
		int			lo = 1;
		int			hi = sp->timecnt;

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

			if (t < sp->ats[mid])
				hi = mid;
			else
				lo = mid + 1;
		}
		i = lo;
	}
	j = sp->types[i - 1];
	ttisp = &sp->ttis[j];
	*before_gmtoff = ttisp->tt_gmtoff;
	*before_isdst = ttisp->tt_isdst;
	*boundary = sp->ats[i];
	j = sp->types[i];
	ttisp = &sp->ttis[j];
	*after_gmtoff = ttisp->tt_gmtoff;
	*after_isdst = ttisp->tt_isdst;
	return 1;
}

/*
 * If the given timezone uses only one GMT offset, store that offset
 * into *gmtoff and return TRUE, else return FALSE.
 */
bool
pg_get_timezone_offset(const pg_tz *tz, long int *gmtoff)
{
	/*
	 * The zone could have more than one ttinfo, if it's historically used
	 * more than one abbreviation.	We return TRUE as long as they all have
	 * the same gmtoff.
	 */
	const struct state *sp;
	int			i;

	sp = &tz->state;
	for (i = 1; i < sp->typecnt; i++)
	{
		if (sp->ttis[i].tt_gmtoff != sp->ttis[0].tt_gmtoff)
			return false;
	}
	*gmtoff = sp->ttis[0].tt_gmtoff;
	return true;
}

/*
 * Return the name of the current timezone
 */
const char *
pg_get_timezone_name(pg_tz *tz)
{
	if (tz)
		return tz->TZname;
	return NULL;
}

/*
 * Check whether timezone is acceptable.
 *
 * What we are doing here is checking for leap-second-aware timekeeping.
 * We need to reject such TZ settings because they'll wreak havoc with our
 * date/time arithmetic.
 */
bool
pg_tz_acceptable(pg_tz *tz)
{
	struct pg_tm *tt;
	pg_time_t	time2000;

	/*
	 * To detect leap-second timekeeping, run pg_localtime for what should be
	 * GMT midnight, 2000-01-01.  Insist that the tm_sec value be zero; any
	 * other result has to be due to leap seconds.
	 */
	time2000 = (POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY;
	tt = pg_localtime(&time2000, tz);
	if (!tt || tt->tm_sec != 0)
		return false;

	return true;
}
