if (tz == NULL)  tz = TZDEFAULT; else if (*tz == '\0')
if (tz && *tz == '\0')
tzset_internal (always)     int always;{  static int is_initialized;  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, 0, NULL);  if (__use_tzfile)    return;  /* No data file found.  Default to UTC if nothing specified.  */  if (tz == NULL || *tz == '\0'      || (TZDEFAULT != NULL && strcmp (tz, TZDEFAULT) == 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;      goto out;    }  /* 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 = strdupa (tz);  if (sscanf (tz, "%[^0-9,+-]", tzbuf) != 1 ||      (l = strlen (tzbuf)) < 3)    goto out;  tz_rules[0].name = __tzstring (tzbuf);  tz += l;  /* Figure out the standard offset from UTC.  */  if (*tz == '\0' || (*tz != '+' && *tz != '-' && !isdigit (*tz)))    goto out;  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:      goto out;    case 1:      mm = 0;    case 2:      ss = 0;    case 3:      break;    }  tz_rules[0].offset *= (min (ss, 59) + (min (mm, 59) * 60) +			 (min (hh, 24) * 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;	      return;	    }	}    }  else    {      /* There is no DST.  */      tz_rules[1].name = tz_rules[0].name;      tz_rules[1].offset = tz_rules[0].offset;      goto out;    } done_names:  /* 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:  __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;  }}