glibc/time/tzset.c

/* Copyright (C) 1991, 92, 93, 94, 95, 96, 97 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 <bits/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));
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)) internal_function;
static int tz_compute __P ((time_t timer, const struct tm *tm))
     internal_function;
static void tzset_internal __P ((int always)) internal_function;

/* 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
internal_function
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;
      free (tzbuf);
      return;
    }

 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))
	    return;
	  tzr->d = (unsigned short int) strtoul (tz, &end, 10);
	  if (end == tz || tzr->d > 365)
	    return;
	  else if (tzr->type == J1 && tzr->d == 0)
	    return;
	  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)
	    return;
	  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
	return;

      if (*tz != '\0' && *tz != '/' && *tz != ',')
	return;
      else if (*tz == '/')
	{
	  /* Get the time of day of the change.  */
	  ++tz;
	  if (*tz == '\0')
	    return;
	  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;
    }
}

/* 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
internal_function
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
internal_function
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;

  __daylight = timer >= tz_rules[0].change && timer < tz_rules[1].change;
  __timezone = -tz_rules[__daylight ? 1 : 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 = NULL;
    }
  else
    {
      __offtime (timer, 0, tp);
      if (! tz_compute (*timer, tp))
	tp = NULL;
      leap_correction = 0L;
      leap_extra_secs = 0;
    }

  if (tp)
    {
      if (use_localtime)
	{
	  tp->tm_isdst = __daylight;
	  tp->tm_zone = __tzname[__daylight];
	  tp->tm_gmtoff = __timezone;
	}
      else
	{
	  tp->tm_isdst = 0;
	  tp->tm_zone = "GMT";
	  tp->tm_gmtoff = 0L;
	}

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

  __libc_lock_unlock (tzset_lock);

  return tp;
}