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Don't warn about valid time zone abbreviations.  POSIX through 2000
says that an abbreviation cannot start with ':', and cannot contain
',', '-', '+', NUL, or a digit.  POSIX from 2001 on changes this
rule to say that an abbreviation can contain only '-', '+', and
alphanumeric characters from the portable character set in the
current locale.  To be portable to both sets of rules, an abbreviation
must therefore use only ASCII letters."  Adapted from tzcode2015f.
OK deraadt@ mestre@

/*	$OpenBSD: zdump.c,v 1.14 2016/03/15 19:50:48 millert Exp $ */
/*
** This file is in the public domain, so clarified as of
** 2009-05-17 by Arthur David Olson.
*/

/*
** This code has been made independent of the rest of the time
** conversion package to increase confidence in the verification it provides.
** You can use this code to help in verifying other implementations.
*/

#include <ctype.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>

#define ZDUMP_LO_YEAR	(-500)
#define ZDUMP_HI_YEAR	2500

#define MAX_STRING_LENGTH	1024

#define TRUE		1
#define FALSE		0

#define SECSPERMIN	60
#define MINSPERHOUR	60
#define SECSPERHOUR	(SECSPERMIN * MINSPERHOUR)
#define HOURSPERDAY	24
#define EPOCH_YEAR	1970
#define TM_YEAR_BASE	1900
#define DAYSPERNYEAR	365

#define SECSPERDAY	((long) SECSPERHOUR * HOURSPERDAY)
#define SECSPERNYEAR	(SECSPERDAY * DAYSPERNYEAR)
#define SECSPERLYEAR	(SECSPERNYEAR + SECSPERDAY)

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

#ifndef isleap_sum
/*
** See tzfile.h for details on isleap_sum.
*/
#define isleap_sum(a, b)	isleap((a) % 400 + (b) % 400)
#endif /* !defined isleap_sum */

extern char	**environ;
extern char	*tzname[2];
extern char 	*__progname;

time_t		absolute_min_time;
time_t		absolute_max_time;
size_t		longest;
int		warned;

static char 		*abbr(struct tm *tmp);
static void		abbrok(const char *abbrp, const char *zone);
static long		delta(struct tm *newp, struct tm *oldp);
static void		dumptime(const struct tm *tmp);
static time_t		hunt(char *name, time_t lot, time_t	hit);
static void		setabsolutes(void);
static void		show(char *zone, time_t t, int v);
static const char 	*tformat(void);
static time_t		yeartot(long y);
static void		usage(void);

static void
abbrok(const char * const abbrp, const char * const zone)
{
	const char 	*cp;
	char 		*wp;

	if (warned)
		return;
	cp = abbrp;
	wp = NULL;
	while (isascii((unsigned char)*cp) &&
	    (isalnum((unsigned char)*cp) || *cp == '-' || *cp == '+'))
		++cp;
	if (cp - abbrp < 3)
		wp = "has fewer than 3 characters";
	else if (cp - abbrp > 6)
		wp = "has more than 6 characters";
	else if (*cp)
		wp = "has characters other than ASCII alphanumerics, '-' or '+'";
	else
		return;
	fflush(stdout);
	fprintf(stderr, "%s: warning: zone \"%s\" abbreviation \"%s\" %s\n",
		__progname, zone, abbrp, wp);
	warned = TRUE;
}

static void
usage(void)
{
	fprintf(stderr, "usage: %s [-v] [-c [loyear,]hiyear] zonename ...\n",
	    __progname);
	exit(EXIT_FAILURE);
}

int
main(int argc, char *argv[])
{
	int		i, c, vflag = 0;
	char		*cutarg = NULL;
	long		cutloyear = ZDUMP_LO_YEAR;
	long		cuthiyear = ZDUMP_HI_YEAR;
	time_t		cutlotime = 0, cuthitime = 0;
	time_t		now, t, newt;
	struct tm	tm, newtm, *tmp, *newtmp;
	char		**fakeenv;

	if (pledge("stdio rpath", NULL) == -1) {
		perror("pledge");
		exit(1);
	}

	while ((c = getopt(argc, argv, "c:v")) == 'c' || c == 'v') {
		switch (c) {
		case 'v':
			vflag = 1;
			break;
		case 'c':
			cutarg = optarg;
			break;
		default:
			usage();
			break;
		}
	}
	if (c != -1 ||
	    (optind == argc - 1 && strcmp(argv[optind], "=") == 0)) {
		usage();
	}
	if (vflag) {
		if (cutarg != NULL) {
			long	lo, hi;
			char	dummy;

			if (sscanf(cutarg, "%ld%c", &hi, &dummy) == 1) {
				cuthiyear = hi;
			} else if (sscanf(cutarg, "%ld,%ld%c",
			    &lo, &hi, &dummy) == 2) {
				cutloyear = lo;
				cuthiyear = hi;
			} else {
				fprintf(stderr, "%s: wild -c argument %s\n",
				    __progname, cutarg);
				exit(EXIT_FAILURE);
			}
		}
		setabsolutes();
		cutlotime = yeartot(cutloyear);
		cuthitime = yeartot(cuthiyear);
	}
	time(&now);
	longest = 0;
	for (i = optind; i < argc; ++i)
		if (strlen(argv[i]) > longest)
			longest = strlen(argv[i]);

	{
		int	from, to;

		for (i = 0; environ[i] != NULL; ++i)
			continue;
		fakeenv = reallocarray(NULL, i + 2, sizeof *fakeenv);
		if (fakeenv == NULL ||
		    (fakeenv[0] = malloc(longest + 4)) == NULL) {
			perror(__progname);
			exit(EXIT_FAILURE);
		}
		to = 0;
		strlcpy(fakeenv[to++], "TZ=", longest + 4);
		for (from = 0; environ[from] != NULL; ++from)
			if (strncmp(environ[from], "TZ=", 3) != 0)
				fakeenv[to++] = environ[from];
		fakeenv[to] = NULL;
		environ = fakeenv;
	}
	for (i = optind; i < argc; ++i) {
		char	buf[MAX_STRING_LENGTH];

		strlcpy(&fakeenv[0][3], argv[i], longest + 1);
		if (!vflag) {
			show(argv[i], now, FALSE);
			continue;
		}
		warned = FALSE;
		t = absolute_min_time;
		show(argv[i], t, TRUE);
		t += SECSPERHOUR * HOURSPERDAY;
		show(argv[i], t, TRUE);
		if (t < cutlotime)
			t = cutlotime;
		tmp = localtime(&t);
		if (tmp != NULL) {
			tm = *tmp;
			strlcpy(buf, abbr(&tm), sizeof buf);
		}
		for ( ; ; ) {
			if (t >= cuthitime || t >= cuthitime - SECSPERHOUR * 12)
				break;
			newt = t + SECSPERHOUR * 12;
			newtmp = localtime(&newt);
			if (newtmp != NULL)
				newtm = *newtmp;
			if ((tmp == NULL || newtmp == NULL) ? (tmp != newtmp) :
			    (delta(&newtm, &tm) != (newt - t) ||
			    newtm.tm_isdst != tm.tm_isdst ||
			    strcmp(abbr(&newtm), buf) != 0)) {
				newt = hunt(argv[i], t, newt);
				newtmp = localtime(&newt);
				if (newtmp != NULL) {
					newtm = *newtmp;
					strlcpy(buf, abbr(&newtm), sizeof buf);
				}
			}
			t = newt;
			tm = newtm;
			tmp = newtmp;
		}
		t = absolute_max_time;
		t -= SECSPERHOUR * HOURSPERDAY;
		show(argv[i], t, TRUE);
		t += SECSPERHOUR * HOURSPERDAY;
		show(argv[i], t, TRUE);
	}
	if (fflush(stdout) || ferror(stdout)) {
		fprintf(stderr, "%s: ", __progname);
		perror("Error writing to standard output");
		exit(EXIT_FAILURE);
	}
	return 0;
}

static void
setabsolutes(void)
{
	time_t t = 0, t1 = 1;

	while (t < t1) {
		t = t1;
		t1 = 2 * t1 + 1;
	}

	absolute_max_time = t;
	t = -t;
	absolute_min_time = t - 1;
	if (t < absolute_min_time)
		absolute_min_time = t;
}

static time_t
yeartot(const long y)
{
	long	myy = EPOCH_YEAR, seconds;
	time_t	t = 0;

	while (myy != y) {
		if (myy < y) {
			seconds = isleap(myy) ? SECSPERLYEAR : SECSPERNYEAR;
			++myy;
			if (t > absolute_max_time - seconds) {
				t = absolute_max_time;
				break;
			}
			t += seconds;
		} else {
			--myy;
			seconds = isleap(myy) ? SECSPERLYEAR : SECSPERNYEAR;
			if (t < absolute_min_time + seconds) {
				t = absolute_min_time;
				break;
			}
			t -= seconds;
		}
	}
	return t;
}

static time_t
hunt(char *name, time_t lot, time_t hit)
{
	time_t			t;
	long			diff;
	struct tm		lotm, *lotmp;
	struct tm		tm, *tmp;
	char			loab[MAX_STRING_LENGTH];

	lotmp = localtime(&lot);
	if (lotmp != NULL) {
		lotm = *lotmp;
		strlcpy(loab, abbr(&lotm), sizeof loab);
	}
	for ( ; ; ) {
		diff = (long) (hit - lot);
		if (diff < 2)
			break;
		t = lot;
		t += diff / 2;
		if (t <= lot)
			++t;
		else if (t >= hit)
			--t;
		tmp = localtime(&t);
		if (tmp != NULL)
			tm = *tmp;
		if ((lotmp == NULL || tmp == NULL) ? (lotmp == tmp) :
		    (delta(&tm, &lotm) == (t - lot) &&
		    tm.tm_isdst == lotm.tm_isdst &&
		    strcmp(abbr(&tm), loab) == 0)) {
			lot = t;
			lotm = tm;
			lotmp = tmp;
		} else
			hit = t;
	}
	show(name, lot, TRUE);
	show(name, hit, TRUE);
	return hit;
}

/*
** Thanks to Paul Eggert for logic used in delta.
*/

static long
delta(struct tm *newp, struct tm *oldp)
{
	long	result;
	int	tmy;

	if (newp->tm_year < oldp->tm_year)
		return -delta(oldp, newp);
	result = 0;
	for (tmy = oldp->tm_year; tmy < newp->tm_year; ++tmy)
		result += DAYSPERNYEAR + isleap_sum(tmy, TM_YEAR_BASE);
	result += newp->tm_yday - oldp->tm_yday;
	result *= HOURSPERDAY;
	result += newp->tm_hour - oldp->tm_hour;
	result *= MINSPERHOUR;
	result += newp->tm_min - oldp->tm_min;
	result *= SECSPERMIN;
	result += newp->tm_sec - oldp->tm_sec;
	return result;
}

static void
show(char *zone, time_t t, int v)
{
	struct tm 	*tmp;

	printf("%-*s  ", (int) longest, zone);
	if (v) {
		tmp = gmtime(&t);
		if (tmp == NULL) {
			printf(tformat(), t);
		} else {
			dumptime(tmp);
			printf(" UTC");
		}
		printf(" = ");
	}
	tmp = localtime(&t);
	dumptime(tmp);
	if (tmp != NULL) {
		if (*abbr(tmp) != '\0')
			printf(" %s", abbr(tmp));
		if (v) {
			printf(" isdst=%d", tmp->tm_isdst);
#ifdef TM_GMTOFF
			printf(" gmtoff=%ld", tmp->TM_GMTOFF);
#endif /* defined TM_GMTOFF */
		}
	}
	printf("\n");
	if (tmp != NULL && *abbr(tmp) != '\0')
		abbrok(abbr(tmp), zone);
}

static char *
abbr(struct tm *tmp)
{
	char 		*result;
	static char	nada;

	if (tmp->tm_isdst != 0 && tmp->tm_isdst != 1)
		return &nada;
	result = tzname[tmp->tm_isdst];
	return (result == NULL) ? &nada : result;
}

/*
** The code below can fail on certain theoretical systems;
** it works on all known real-world systems as of 2004-12-30.
*/

static const char *
tformat(void)
{
	return "%lld";
}

static void
dumptime(const struct tm *timeptr)
{
	static const char wday_name[][3] = {
		"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
	};
	static const char mon_name[][3] = {
		"Jan", "Feb", "Mar", "Apr", "May", "Jun",
		"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
	};
	const char	*wn, *mn;
	int		lead, trail;

	if (timeptr == NULL) {
		printf("NULL");
		return;
	}
	/*
	** The packaged versions of localtime and gmtime never put out-of-range
	** values in tm_wday or tm_mon, but since this code might be compiled
	** with other (perhaps experimental) versions, paranoia is in order.
	*/
	if (timeptr->tm_wday < 0 || timeptr->tm_wday >=
	    (int) (sizeof wday_name / sizeof wday_name[0]))
		wn = "???";
	else
		wn = wday_name[timeptr->tm_wday];
	if (timeptr->tm_mon < 0 || timeptr->tm_mon >=
	    (int) (sizeof mon_name / sizeof mon_name[0]))
		mn = "???";
	else
		mn = mon_name[timeptr->tm_mon];
	printf("%.3s %.3s%3d %.2d:%.2d:%.2d ",
	    wn, mn,
	    timeptr->tm_mday, timeptr->tm_hour,
	    timeptr->tm_min, timeptr->tm_sec);
#define DIVISOR	10
	trail = timeptr->tm_year % DIVISOR + TM_YEAR_BASE % DIVISOR;
	lead = timeptr->tm_year / DIVISOR + TM_YEAR_BASE / DIVISOR +
		trail / DIVISOR;
	trail %= DIVISOR;
	if (trail < 0 && lead > 0) {
		trail += DIVISOR;
		--lead;
	} else if (lead < 0 && trail > 0) {
		trail -= DIVISOR;
		++lead;
	}
	if (lead == 0)
		printf("%d", trail);
	else
		printf("%d%d", lead, ((trail < 0) ? -trail : trail));
}