strptime.c

#include <sys/cdefs.h>
#include <assert.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

/*
 *	strptime - something like the opposite of date...
 *
 * Tue Aug 10 23:23:45 EDT 1999
 */

static const char *argv0 = "strptime";

int main(int, char *[]);

static void set_tm_wday(struct tm *);
static void set_tm_yday(struct tm *);

int
main(argc, argv)
	int argc;
	char *argv[];
{
	struct tm tmt;
	time_t then;
	const char *tfmt = "%a %b %d %T EDT %Y"; /* ala date(1) */
	char *ttime;
	char *tright;

	argv0 = (argv0 = strrchr(argv[0], '/')) ? argv0 + 1 : argv[0];

	if (argc < 2 || argc > 3) {
		fprintf(stderr, "usage: %s [fmt] string\n", argv0);
		exit(2);
	}
	if (argc == 3) {
		tfmt = argv[1];
		ttime = argv[2];
	} else {
		ttime = argv[1];
	}

	if (!(tright = strptime(ttime, tfmt, &tmt))) {
		fprintf(stderr, "%s: date format '%s' did not match date string '%s'.\n", argv0, tfmt, ttime);
		exit(1);
	}
	if (*tright) {
		printf("%s: unprocessed remainder: '%s'.\n", argv0, tright);
	}
	/*
	 * This is OS X or some older *BSD whose strptime() has not yet been
	 * enhanced to fill out tm_wday and/or tm_yday when possible.
	 *
	 * borrowed from:
	 *
	 * https://github.com/stedolan/jq/commit/c538237f4e4c381d35f1c15497c95f659fd55850
	 */
	if (tmt.tm_wday == 8 && tmt.tm_mday != 0 && tmt.tm_mon >= 0 && tmt.tm_mon <= 11) {
		set_tm_wday(&tmt);
	}
	if (tmt.tm_yday == 367 && tmt.tm_mday != 0 && tmt.tm_mon >= 0 && tmt.tm_mon <= 11) {
		set_tm_yday(&tmt);
	}
	tmt.tm_isdst = -1;		/* make mktime() guess the right timezone */
	if ((then = mktime(&tmt)) < 0) {
		struct tm *tmy;
		time_t timenow;
		
		/* some formats don't include the year, so we try to provide it
		 * using the current year....
		 */
		timenow = time((time_t *) NULL);
		tmy = localtime(&timenow);
		tmt.tm_year = tmy->tm_year;
		then = mktime(&tmt);
	}
	if (then < 0) {
		fprintf(stderr, "%s: unable to make time!\n", argv0);
		exit(1);
	}
	printf("'%s' == %ld == %s\n", ttime, (long) then, ctime(&then));

	exit(0);
	/* NOTREACHED */
}


/*
 * Compute and set tm_wday
 */
static void
set_tm_wday(struct tm *tm)
{
	int century;
	int year;
	int mon;
	int wday;

	/*
	 * https://en.wikipedia.org/wiki/Determination_of_the_day_of_the_week#Gauss.27s_algorithm
	 * https://cs.uwaterloo.ca/~alopez-o/math-faq/node73.html
	 *
	 * Tested with dates from 1900-01-01 through 2100-01-01.
	 *
	 * This algorithm produces the wrong day-of-the-week number for dates in
	 * the range 1900-01-01..1900-02-28, and for 2100-01-01..2100-02-28.
	 */
	century = (1900 + tm->tm_year) / 100;
	year = (1900 + tm->tm_year) % 100;
	if (tm->tm_mon < 2) {
		year--;
	}
	/*
	 * The month value in the wday computation below is shifted so that
	 * March is 1, April is 2, .., January is 11, and February is 12.
	 */
	mon = tm->tm_mon - 1;
	if (mon < 1) {
		mon += 12;
	}
	wday = (tm->tm_mday +
	        (int) lrint(floor((2.6 * mon - 0.2))) +
	        year +
	        (int) lrint(floor(year / 4.0)) +
	        (int) lrint(floor(century / 4.0)) -
	        2 * century) % 7;
	if (wday < 0) {
		wday += 7;
	}
#if 0
	/* See commentary above */
	assert(wday == tm->tm_wday || tm->tm_wday == 8);
#endif
	tm->tm_wday = wday;
}

/*
 * Compute and set tm_yday.
 */
static void
set_tm_yday(struct tm *tm)
{
	static const int d[] = {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334};
	int mon;
	int year;
	int leap_day;
	int yday;

	mon = tm->tm_mon;
	year = 1900 + tm->tm_year;
	leap_day = 0;
	if (tm->tm_mon > 1 &&
	    ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0))) {
		leap_day = 1;
	}

	/* Bound check index into d[] */
	if (mon < 0) {
		mon = -mon;
	}
	if (mon > 11) {
		mon %= 12;
	}
	yday = d[mon] + leap_day + tm->tm_mday - 1;
	assert(yday == tm->tm_yday || tm->tm_yday == 367);
	tm->tm_yday = yday;

	return;
}

#if 0

/*	$NetBSD: strptime.c,v 1.18 1999/04/29 02:58:30 tv Exp $	*/

/*-
 * Copyright (c) 1997, 1998 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code was contributed to The NetBSD Foundation by Klaus Klein.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *        This product includes software developed by the NetBSD
 *        Foundation, Inc. and its contributors.
 * 4. Neither the name of The NetBSD Foundation nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: strptime.c,v 1.18 1999/04/29 02:58:30 tv Exp $");
#endif

/* #include "namespace.h" */
#include <sys/localedef.h>
#include <ctype.h>
#include <locale.h>
#include <string.h>
#include <time.h>
#include <tzfile.h>

#ifdef __weak_alias
__weak_alias(strptime,_strptime);
#endif

#define	_ctloc(x)		__CONCAT(_CurrentTimeLocale->,x)

/*
 * We do not implement alternate representations. However, we always
 * check whether a given modifier is allowed for a certain conversion.
 */
#define ALT_E			0x01
#define ALT_O			0x02
#define	LEGAL_ALT(x)		{ if (alt_format & ~(x)) return (0); }


static	int conv_num __P((const char **, int *, int, int));


char *
strptime(buf, fmt, tm)
	const char *buf, *fmt;
	struct tm *tm;
{
	char c;
	const char *bp;
	size_t len = 0;
	int alt_format, i, split_year = 0;

	bp = buf;

	while ((c = *fmt) != '\0') {
		/* Clear `alternate' modifier prior to new conversion. */
		alt_format = 0;

		/* Eat up white-space. */
		if (isspace(c)) {
			while (isspace(*bp))
				bp++;

			fmt++;
			continue;
		}
				
		if ((c = *fmt++) != '%')
			goto literal;


again:		switch (c = *fmt++) {
		case '%':	/* "%%" is converted to "%". */
literal:
			if (c != *bp++)
				return (0);
			break;

		/*
		 * "Alternative" modifiers. Just set the appropriate flag
		 * and start over again.
		 */
		case 'E':	/* "%E?" alternative conversion modifier. */
			LEGAL_ALT(0);
			alt_format |= ALT_E;
			goto again;

		case 'O':	/* "%O?" alternative conversion modifier. */
			LEGAL_ALT(0);
			alt_format |= ALT_O;
			goto again;
			
		/*
		 * "Complex" conversion rules, implemented through recursion.
		 */
		case 'c':	/* Date and time, using the locale's format. */
			LEGAL_ALT(ALT_E);
			if (!(bp = strptime(bp, _ctloc(d_t_fmt), tm)))
				return (0);
			break;

		case 'D':	/* The date as "%m/%d/%y". */
			LEGAL_ALT(0);
			if (!(bp = strptime(bp, "%m/%d/%y", tm)))
				return (0);
			break;

		case 'R':	/* The time as "%H:%M". */
			LEGAL_ALT(0);
			if (!(bp = strptime(bp, "%H:%M", tm)))
				return (0);
			break;

		case 'r':	/* The time in 12-hour clock representation. */
			LEGAL_ALT(0);
			if (!(bp = strptime(bp, _ctloc(t_fmt_ampm), tm)))
				return (0);
			break;

		case 'T':	/* The time as "%H:%M:%S". */
			LEGAL_ALT(0);
			if (!(bp = strptime(bp, "%H:%M:%S", tm)))
				return (0);
			break;

		case 'X':	/* The time, using the locale's format. */
			LEGAL_ALT(ALT_E);
			if (!(bp = strptime(bp, _ctloc(t_fmt), tm)))
				return (0);
			break;

		case 'x':	/* The date, using the locale's format. */
			LEGAL_ALT(ALT_E);
			if (!(bp = strptime(bp, _ctloc(d_fmt), tm)))
				return (0);
			break;

		/*
		 * "Elementary" conversion rules.
		 */
		case 'A':	/* The day of week, using the locale's form. */
		case 'a':
			LEGAL_ALT(0);
			for (i = 0; i < 7; i++) {
				/* Full name. */
				len = strlen(_ctloc(day[i]));
				if (strncasecmp(_ctloc(day[i]), bp, len) == 0)
					break;

				/* Abbreviated name. */
				len = strlen(_ctloc(abday[i]));
				if (strncasecmp(_ctloc(abday[i]), bp, len) == 0)
					break;
			}

			/* Nothing matched. */
			if (i == 7)
				return (0);

			tm->tm_wday = i;
			bp += len;
			break;

		case 'B':	/* The month, using the locale's form. */
		case 'b':
		case 'h':
			LEGAL_ALT(0);
			for (i = 0; i < 12; i++) {
				/* Full name. */
				len = strlen(_ctloc(mon[i]));
				if (strncasecmp(_ctloc(mon[i]), bp, len) == 0)
					break;

				/* Abbreviated name. */
				len = strlen(_ctloc(abmon[i]));
				if (strncasecmp(_ctloc(abmon[i]), bp, len) == 0)
					break;
			}

			/* Nothing matched. */
			if (i == 12)
				return (0);

			tm->tm_mon = i;
			bp += len;
			break;

		case 'C':	/* The century number. */
			LEGAL_ALT(ALT_E);
			if (!(conv_num(&bp, &i, 0, 99)))
				return (0);

			if (split_year) {
				tm->tm_year = (tm->tm_year % 100) + (i * 100);
			} else {
				tm->tm_year = i * 100;
				split_year = 1;
			}
			break;

		case 'd':	/* The day of month. */
		case 'e':
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_mday, 1, 31)))
				return (0);
			break;

		case 'k':	/* The hour (24-hour clock representation). */
			LEGAL_ALT(0);
			/* FALLTHROUGH */
		case 'H':
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_hour, 0, 23)))
				return (0);
			break;

		case 'l':	/* The hour (12-hour clock representation). */
			LEGAL_ALT(0);
			/* FALLTHROUGH */
		case 'I':
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_hour, 1, 12)))
				return (0);
			if (tm->tm_hour == 12)
				tm->tm_hour = 0;
			break;

		case 'j':	/* The day of year. */
			LEGAL_ALT(0);
			if (!(conv_num(&bp, &i, 1, 366)))
				return (0);
			tm->tm_yday = i - 1;
			break;

		case 'M':	/* The minute. */
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_min, 0, 59)))
				return (0);
			break;

		case 'm':	/* The month. */
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &i, 1, 12)))
				return (0);
			tm->tm_mon = i - 1;
			break;

		case 'p':	/* The locale's equivalent of AM/PM. */
			LEGAL_ALT(0);
			/* AM? */
			if (strcasecmp(_ctloc(am_pm[0]), bp) == 0) {
				if (tm->tm_hour > 11)
					return (0);

				bp += strlen(_ctloc(am_pm[0]));
				break;
			}
			/* PM? */
			else if (strcasecmp(_ctloc(am_pm[1]), bp) == 0) {
				if (tm->tm_hour > 11)
					return (0);

				tm->tm_hour += 12;
				bp += strlen(_ctloc(am_pm[1]));
				break;
			}

			/* Nothing matched. */
			return (0);

		case 'S':	/* The seconds. */
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_sec, 0, 61)))
				return (0);
			break;

		case 'U':	/* The week of year, beginning on sunday. */
		case 'W':	/* The week of year, beginning on monday. */
			LEGAL_ALT(ALT_O);
			/*
			 * XXX This is bogus, as we can not assume any valid
			 * information present in the tm structure at this
			 * point to calculate a real value, so just check the
			 * range for now.
			 */
			 if (!(conv_num(&bp, &i, 0, 53)))
				return (0);
			 break;

		case 'w':	/* The day of week, beginning on sunday. */
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_wday, 0, 6)))
				return (0);
			break;

		case 'Y':	/* The year. */
			LEGAL_ALT(ALT_E);
			if (!(conv_num(&bp, &i, 0, 9999)))
				return (0);

			tm->tm_year = i - TM_YEAR_BASE;
			break;

		case 'y':	/* The year within 100 years of the epoch. */
			LEGAL_ALT(ALT_E | ALT_O);
			if (!(conv_num(&bp, &i, 0, 99)))
				return (0);

			if (split_year) {
				tm->tm_year = ((tm->tm_year / 100) * 100) + i;
				break;
			}
			split_year = 1;
			if (i <= 68)
				tm->tm_year = i + 2000 - TM_YEAR_BASE;
			else
				tm->tm_year = i + 1900 - TM_YEAR_BASE;
			break;

		/*
		 * Miscellaneous conversions.
		 */
		case 'n':	/* Any kind of white-space. */
		case 't':
			LEGAL_ALT(0);
			while (isspace(*bp))
				bp++;
			break;


		default:	/* Unknown/unsupported conversion. */
			return (0);
		}


	}

	/* LINTED functional specification */
	return ((char *)bp);
}


static int
conv_num(buf, dest, llim, ulim)
	const char **buf;
	int *dest;
	int llim, ulim;
{
	int result = 0;

	/* The limit also determines the number of valid digits. */
	int rulim = ulim;

	if (**buf < '0' || **buf > '9')
		return (0);

	do {
		result *= 10;
		result += *(*buf)++ - '0';
		rulim /= 10;
	} while ((result * 10 <= ulim) && rulim && **buf >= '0' && **buf <= '9');

	if (result < llim || result > ulim)
		return (0);

	*dest = result;
	return (1);
}
#endif