glibc/time/tzset.c

/* Copyright (C) 1991,92,93,94,95,96,97,98 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

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

   The GNU C Library 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <ctype.h>
#include <errno.h>
#include <libc-lock.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

/* Defined in mktime.c.  */
extern const unsigned short int __mon_yday[2][13];

/* Defined in localtime.c.  */
extern struct tm _tmbuf;

#define NOID
#include "tzfile.h"

extern int __use_tzfile;
extern void __tzfile_read __P ((const char *file));
extern int __tzfile_compute __P ((time_t timer, int use_localtime,
				  long int *leap_correct, int *leap_hit,
				  struct tm *tp));
extern void __tzfile_default __P ((const char *std, const char *dst,
				   long int stdoff, long int dstoff));
extern char *__tzstring __P ((const char *string));

char *__tzname[2] = { (char *) "GMT", (char *) "GMT" };
int __daylight = 0;
long int __timezone = 0L;

weak_alias (__tzname, tzname)
weak_alias (__daylight, daylight)
weak_alias (__timezone, timezone)

/* This locks all the state variables in tzfile.c and this file.  */
__libc_lock_define (static, tzset_lock)


#define	min(a, b)	((a) < (b) ? (a) : (b))
#define	max(a, b)	((a) > (b) ? (a) : (b))
#define	sign(x)		((x) < 0 ? -1 : 1)


/* This structure contains all the information about a
   timezone given in the POSIX standard TZ envariable.  */
typedef struct
  {
    const char *name;

    /* When to change.  */
    enum { J0, J1, M } type;	/* Interpretation of:  */
    unsigned short int m, n, d;	/* Month, week, day.  */
    unsigned int secs;		/* Time of day.  */

    long int offset;		/* Seconds east of GMT (west if < 0).  */

    /* We cache the computed time of change for a
       given year so we don't have to recompute it.  */
    time_t change;	/* When to change to this zone.  */
    int computed_for;	/* Year above is computed for.  */
  } tz_rule;

/* tz_rules[0] is standard, tz_rules[1] is daylight.  */
static tz_rule tz_rules[2];


static int compute_change __P ((tz_rule *rule, int year));
static int tz_compute __P ((time_t timer, const struct tm *tm));
static void tzset_internal __P ((int always));

/* Header for a list of buffers containing time zone strings.  */
struct tzstring_head
{
  struct tzstring_head *next;
  /* The buffer itself immediately follows the header.
     The buffer contains zero or more (possibly overlapping) strings.
     The last string is followed by 2 '\0's instead of the usual 1.  */
};

/* First in a list of buffers containing time zone strings.
   All the buffers but the last are read-only.  */
static struct
{
  struct tzstring_head head;
  char data[48];
} tzstring_list;

/* Size of the last buffer in the list, not counting its header.  */
static size_t tzstring_last_buffer_size = sizeof tzstring_list.data;

/* Allocate a time zone string with given contents.
   The string will never be moved or deallocated.
   However, its contents may be shared with other such strings.  */
char *
__tzstring (string)
     const char *string;
{
  struct tzstring_head *h = &tzstring_list.head;
  size_t needed;
  char *p;

  /* Look through time zone string list for a duplicate of this one.  */
  for (h = &tzstring_list.head;  ;  h = h->next)
    {
      for (p = (char *) (h + 1);  p[0] | p[1];  ++p)
	if (strcmp (p, string) == 0)
	  return p;
      if (! h->next)
	break;
    }

  /* No duplicate was found.  Copy to the end of this buffer if there's room;
     otherwise, append a large-enough new buffer to the list and use it.  */
  ++p;
  needed = strlen (string) + 2; /* Need 2 trailing '\0's after last string.  */

  if ((size_t) ((char *) (h + 1) + tzstring_last_buffer_size - p) < needed)
    {
      size_t buffer_size = tzstring_last_buffer_size;
      while ((buffer_size *= 2) < needed)
	continue;
      if (! (h = h->next = malloc (sizeof *h + buffer_size)))
	return NULL;
      h->next = NULL;
      tzstring_last_buffer_size = buffer_size;
      p = (char *) (h + 1);
    }

  return strncpy (p, string, needed);
}

static char *old_tz = NULL;

/* Interpret the TZ envariable.  */
static void
tzset_internal (always)
     int always;
{
  static int is_initialized = 0;
  register const char *tz;
  register size_t l;
  char *tzbuf;
  unsigned short int hh, mm, ss;
  unsigned short int whichrule;

  if (is_initialized && !always)
    return;
  is_initialized = 1;

  /* Examine the TZ environment variable.  */
  tz = getenv ("TZ");
  if (tz == NULL)
    /* No user specification; use the site-wide default.  */
    tz = TZDEFAULT;
  else if (*tz == '\0')
    /* User specified the empty string; use UTC explicitly.  */
    tz = "Universal";

  /* A leading colon means "implementation defined syntax".
     We ignore the colon and always use the same algorithm:
     try a data file, and if none exists parse the 1003.1 syntax.  */
  if (tz && *tz == ':')
    ++tz;

  /* Check whether the value changes since the last run.  */
  if (old_tz != NULL && tz != NULL && strcmp (tz, old_tz) == 0)
    /* No change, simply return.  */
    return;

  tz_rules[0].name = NULL;
  tz_rules[1].name = NULL;

  /* Save the value of `tz'.  */
  if (old_tz != NULL)
    free (old_tz);
  old_tz = tz ? __strdup (tz) : NULL;

  /* Try to read a data file.  */
  __tzfile_read (tz);
  if (__use_tzfile)
    return;

  /* No data file found.  Default to UTC if nothing specified.  */

  if (tz == NULL || *tz == '\0')
    {
      tz_rules[0].name = tz_rules[1].name = "UTC";
      tz_rules[0].type = tz_rules[1].type = J0;
      tz_rules[0].m = tz_rules[0].n = tz_rules[0].d = 0;
      tz_rules[1].m = tz_rules[1].n = tz_rules[1].d = 0;
      tz_rules[0].secs = tz_rules[1].secs = 0;
      tz_rules[0].offset = tz_rules[1].offset = 0L;
      tz_rules[0].change = tz_rules[1].change = (time_t) -1;
      tz_rules[0].computed_for = tz_rules[1].computed_for = 0;
      return;
    }

  /* Clear out old state and reset to unnamed UTC.  */
  memset (tz_rules, 0, sizeof tz_rules);
  tz_rules[0].name = tz_rules[1].name = "";

  /* Get the standard timezone name.  */
  tzbuf = malloc (strlen (tz) + 1);
  if (! tzbuf)
    {
      /* Clear the old tz name so we will try again.  */
      free (old_tz);
      old_tz = NULL;
      return;
    }

  if (sscanf (tz, "%[^0-9,+-]", tzbuf) != 1 ||
      (l = strlen (tzbuf)) < 3)
    {
      free (tzbuf);
      return;
    }

  tz_rules[0].name = __tzstring (tzbuf);

  tz += l;

  /* Figure out the standard offset from UTC.  */
  if (*tz == '\0' || (*tz != '+' && *tz != '-' && !isdigit (*tz)))
    {
      free (tzbuf);
      return;
    }

  if (*tz == '-' || *tz == '+')
    tz_rules[0].offset = *tz++ == '-' ? 1L : -1L;
  else
    tz_rules[0].offset = -1L;
  switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
    {
    default:
      free (tzbuf);
      return;
    case 1:
      mm = 0;
    case 2:
      ss = 0;
    case 3:
      break;
    }
  tz_rules[0].offset *= (min (ss, 59) + (min (mm, 59) * 60) +
			 (min (hh, 23) * 60 * 60));

  for (l = 0; l < 3; ++l)
    {
      while (isdigit(*tz))
	++tz;
      if (l < 2 && *tz == ':')
	++tz;
    }

  /* Get the DST timezone name (if any).  */
  if (*tz != '\0')
    {
      char *n = tzbuf + strlen (tzbuf) + 1;
      if (sscanf (tz, "%[^0-9,+-]", n) != 1 ||
	  (l = strlen (n)) < 3)
	goto done_names;	/* Punt on name, set up the offsets.  */

      tz_rules[1].name = __tzstring (n);

      tz += l;

      /* Figure out the DST offset from GMT.  */
      if (*tz == '-' || *tz == '+')
	tz_rules[1].offset = *tz++ == '-' ? 1L : -1L;
      else
	tz_rules[1].offset = -1L;

      switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
	{
	default:
	  /* Default to one hour later than standard time.  */
	  tz_rules[1].offset = tz_rules[0].offset + (60 * 60);
	  break;

	case 1:
	  mm = 0;
	case 2:
	  ss = 0;
	case 3:
	  tz_rules[1].offset *= (min (ss, 59) + (min (mm, 59) * 60) +
				 (min (hh, 23) * (60 * 60)));
	  break;
	}
      for (l = 0; l < 3; ++l)
	{
	  while (isdigit (*tz))
	    ++tz;
	  if (l < 2 && *tz == ':')
	    ++tz;
	}
      if (*tz == '\0' || (tz[0] == ',' && tz[1] == '\0'))
	{
	  /* There is no rule.  See if there is a default rule file.  */
	  __tzfile_default (tz_rules[0].name, tz_rules[1].name,
			    tz_rules[0].offset, tz_rules[1].offset);
	  if (__use_tzfile)
	    {
	      free (old_tz);
	      old_tz = NULL;
	      free (tzbuf);
	      return;
	    }
	}
    }
  else
    {
      /* There is no DST.  */
      tz_rules[1].name = tz_rules[0].name;
      tz_rules[1].offset = tz_rules[0].offset;
      free (tzbuf);
      goto out;
    }

 done_names:
  free (tzbuf);

  /* Figure out the standard <-> DST rules.  */
  for (whichrule = 0; whichrule < 2; ++whichrule)
    {
      register tz_rule *tzr = &tz_rules[whichrule];

      /* Ignore comma to support string following the incorrect
	 specification in early POSIX.1 printings.  */
      tz += *tz == ',';

      /* Get the date of the change.  */
      if (*tz == 'J' || isdigit (*tz))
	{
	  char *end;
	  tzr->type = *tz == 'J' ? J1 : J0;
	  if (tzr->type == J1 && !isdigit (*++tz))
	    goto out;
	  tzr->d = (unsigned short int) strtoul (tz, &end, 10);
	  if (end == tz || tzr->d > 365)
	    goto out;
	  else if (tzr->type == J1 && tzr->d == 0)
	    goto out;
	  tz = end;
	}
      else if (*tz == 'M')
	{
	  int n;
	  tzr->type = M;
	  if (sscanf (tz, "M%hu.%hu.%hu%n",
		      &tzr->m, &tzr->n, &tzr->d, &n) != 3 ||
	      tzr->m < 1 || tzr->m > 12 ||
	      tzr->n < 1 || tzr->n > 5 || tzr->d > 6)
	    goto out;
	  tz += n;
	}
      else if (*tz == '\0')
	{
	  /* United States Federal Law, the equivalent of "M4.1.0,M10.5.0".  */
	  tzr->type = M;
	  if (tzr == &tz_rules[0])
	    {
	      tzr->m = 4;
	      tzr->n = 1;
	      tzr->d = 0;
	    }
	  else
	    {
	      tzr->m = 10;
	      tzr->n = 5;
	      tzr->d = 0;
	    }
	}
      else
	goto out;

      if (*tz != '\0' && *tz != '/' && *tz != ',')
	goto out;
      else if (*tz == '/')
	{
	  /* Get the time of day of the change.  */
	  ++tz;
	  if (*tz == '\0')
	    goto out;
	  switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
	    {
	    default:
	      hh = 2;		/* Default to 2:00 AM.  */
	    case 1:
	      mm = 0;
	    case 2:
	      ss = 0;
	    case 3:
	      break;
	    }
	  for (l = 0; l < 3; ++l)
	    {
	      while (isdigit (*tz))
		++tz;
	      if (l < 2 && *tz == ':')
		++tz;
	    }
	  tzr->secs = (hh * 60 * 60) + (mm * 60) + ss;
	}
      else
	/* Default to 2:00 AM.  */
	tzr->secs = 2 * 60 * 60;

      tzr->computed_for = -1;
    }

 out:
  /* We know the offset now, set `__timezone'.  */
  __timezone = -tz_rules[0].offset;
}

/* Maximum length of a timezone name.  __tz_compute keeps this up to date
   (never decreasing it) when ! __use_tzfile.
   tzfile.c keeps it up to date when __use_tzfile.  */
size_t __tzname_cur_max;

long int
__tzname_max ()
{
  __libc_lock_lock (tzset_lock);

  tzset_internal (0);

  __libc_lock_unlock (tzset_lock);

  return __tzname_cur_max;
}

/* Figure out the exact time (as a time_t) in YEAR
   when the change described by RULE will occur and
   put it in RULE->change, saving YEAR in RULE->computed_for.
   Return nonzero if successful, zero on failure.  */
static int
compute_change (rule, year)
     tz_rule *rule;
     int year;
{
  register time_t t;
  int y;

  if (year != -1 && rule->computed_for == year)
    /* Operations on times in 1969 will be slower.  Oh well.  */
    return 1;

  /* First set T to January 1st, 0:00:00 GMT in YEAR.  */
  t = 0;
  for (y = 1970; y < year; ++y)
    t += SECSPERDAY * (__isleap (y) ? 366 : 365);

  switch (rule->type)
    {
    case J1:
      /* 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.  */
      t += (rule->d - 1) * SECSPERDAY;
      if (rule->d >= 60 && __isleap (year))
	t += SECSPERDAY;
      break;

    case J0:
      /* n - Day of year.
	 Just add SECSPERDAY times the day number to the time of Jan 1st.  */
      t += rule->d * SECSPERDAY;
      break;

    case M:
      /* Mm.n.d - Nth "Dth day" of month M.  */
      {
	unsigned int i;
	int d, m1, yy0, yy1, yy2, dow;
	const unsigned short int *myday =
	  &__mon_yday[__isleap (year)][rule->m];

	/* First add SECSPERDAY for each day in months before M.  */
	t += myday[-1] * SECSPERDAY;

	/* Use Zeller's Congruence to get day-of-week of first day of month. */
	m1 = (rule->m + 9) % 12 + 1;
	yy0 = (rule->m <= 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 += 7;

	/* 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 = rule->d - dow;
	if (d < 0)
	  d += 7;
	for (i = 1; i < rule->n; ++i)
	  {
	    if (d + 7 >= (int) myday[0] - myday[-1])
	      break;
	    d += 7;
	  }

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

  /* T is now the Epoch-relative time of 0:00:00 GMT on the day we want.
     Just add the time of day and local offset from GMT, and we're done.  */

  rule->change = t - rule->offset + rule->secs;
  rule->computed_for = year;
  return 1;
}


/* Figure out the correct timezone for *TIMER and TM (which must be the same)
   and set `__tzname', `__timezone', and `__daylight' accordingly.
   Return nonzero on success, zero on failure.  */
static int
tz_compute (timer, tm)
     time_t timer;
     const struct tm *tm;
{
  if (! compute_change (&tz_rules[0], 1900 + tm->tm_year) ||
      ! compute_change (&tz_rules[1], 1900 + tm->tm_year))
    return 0;
  /* We have to distinguish between northern and southern hemisphere.
     For the later the daylight saving time ends in the next year.
     It is easier to detect this after first computing the time for the
     wrong year since now we simply can compare the times to switch.  */
  if (tz_rules[0].change > tz_rules[1].change
      && ! compute_change (&tz_rules[1], 1900 + tm->tm_year + 1))
    return 0;

  __daylight = tz_rules[0].offset != tz_rules[1].offset;
  __timezone = -tz_rules[0].offset;
  __tzname[0] = (char *) tz_rules[0].name;
  __tzname[1] = (char *) tz_rules[1].name;

  {
    /* Keep __tzname_cur_max up to date.  */
    size_t len0 = strlen (__tzname[0]);
    size_t len1 = strlen (__tzname[1]);
    if (len0 > __tzname_cur_max)
      __tzname_cur_max = len0;
    if (len1 > __tzname_cur_max)
      __tzname_cur_max = len1;
  }

  return 1;
}

/* Reinterpret the TZ environment variable and set `tzname'.  */
#undef tzset

void
__tzset (void)
{
  __libc_lock_lock (tzset_lock);

  tzset_internal (1);

  if (!__use_tzfile)
    {
      /* Set `tzname'.  */
      __tzname[0] = (char *) tz_rules[0].name;
      __tzname[1] = (char *) tz_rules[1].name;
    }

  __libc_lock_unlock (tzset_lock);
}
weak_alias (__tzset, tzset)

/* Return the `struct tm' representation of *TIMER in the local timezone.
   Use local time if USE_LOCALTIME is nonzero, UTC otherwise.  */
struct tm *
__tz_convert (const time_t *timer, int use_localtime, struct tm *tp)
{
  long int leap_correction;
  int leap_extra_secs;

  if (timer == NULL)
    {
      __set_errno (EINVAL);
      return NULL;
    }

  __libc_lock_lock (tzset_lock);

  /* Update internal database according to current TZ setting.
     POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname.
     This is a good idea since this allows at least a bit more parallelism.
     By analogy we apply the same rule to gmtime_r.  */
  tzset_internal (tp == &_tmbuf);

  if (__use_tzfile)
    {
      if (! __tzfile_compute (*timer, use_localtime,
			      &leap_correction, &leap_extra_secs, tp))
	tp = NULL;
    }
  else
    {
      if (! (__offtime (timer, 0, tp) && tz_compute (*timer, tp)))
	tp = NULL;
      leap_correction = 0L;
      leap_extra_secs = 0;
    }

  if (tp)
    {
      if (use_localtime)
	{
	  if (!__use_tzfile)
	    {
	      int isdst = (*timer >= tz_rules[0].change
			   && *timer < tz_rules[1].change);
	      tp->tm_isdst = isdst;
	      tp->tm_zone = __tzname[isdst];
	      tp->tm_gmtoff = tz_rules[isdst].offset;
	    }
	}
      else
	{
	  tp->tm_isdst = 0;
	  tp->tm_zone = "GMT";
	  tp->tm_gmtoff = 0L;
	}

      if (__offtime (timer, tp->tm_gmtoff - leap_correction, tp))
        tp->tm_sec += leap_extra_secs;
      else
	tp = NULL;
    }

  __libc_lock_unlock (tzset_lock);

  return tp;
}