time.c

MC Linux/Unix 终端下文件管理器

/* 
   Unix SMB/Netbios implementation.
   Version 1.9.
   time handling functions
   Copyright (C) Andrew Tridgell 1992-1998
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   This program 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 General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#include "includes.h"

/*
  This stuff was largely rewritten by Paul Eggert <[e-mail]>
  in May 1996 
  */


int serverzone=0;
int extra_time_offset = 0;

extern int DEBUGLEVEL;

#ifndef CHAR_BIT
#define CHAR_BIT 8
#endif

#ifndef TIME_T_MIN
#define TIME_T_MIN ((time_t)0 < (time_t) -1 ? (time_t) 0 \
		    : ~ (time_t) 0 << (sizeof (time_t) * CHAR_BIT - 1))
#endif
#ifndef TIME_T_MAX
#define TIME_T_MAX (~ (time_t) 0 - TIME_T_MIN)
#endif



/*******************************************************************
a gettimeofday wrapper
********************************************************************/
void GetTimeOfDay(struct timeval *tval)
{
#ifdef HAVE_GETTIMEOFDAY_TZ
	gettimeofday(tval,NULL);
#else
	gettimeofday(tval);
#endif
}

#define TM_YEAR_BASE 1900

/*******************************************************************
yield the difference between *A and *B, in seconds, ignoring leap seconds
********************************************************************/
static int tm_diff(struct tm *a, struct tm *b)
{
  int ay = a->tm_year + (TM_YEAR_BASE - 1);
  int by = b->tm_year + (TM_YEAR_BASE - 1);
  int intervening_leap_days =
    (ay/4 - by/4) - (ay/100 - by/100) + (ay/400 - by/400);
  int years = ay - by;
  int days = 365*years + intervening_leap_days + (a->tm_yday - b->tm_yday);
  int hours = 24*days + (a->tm_hour - b->tm_hour);
  int minutes = 60*hours + (a->tm_min - b->tm_min);
  int seconds = 60*minutes + (a->tm_sec - b->tm_sec);

  return seconds;
}

/*******************************************************************
  return the UTC offset in seconds west of UTC, or 0 if it cannot be determined
  ******************************************************************/
static int TimeZone(time_t t)
{
  struct tm *tm = gmtime(&t);
  struct tm tm_utc;
  if (!tm)
    return 0;
  tm_utc = *tm;
  tm = localtime(&t);
  if (!tm)
    return 0;
  return tm_diff(&tm_utc,tm);

}


/*******************************************************************
init the time differences
********************************************************************/
void TimeInit(void)
{
  serverzone = TimeZone(time(NULL));

  if ((serverzone % 60) != 0) {
	  DEBUG(1,("WARNING: Your timezone is not a multiple of 1 minute.\n"));
  }

  DEBUG(4,("Serverzone is %d\n",serverzone));
}


/*******************************************************************
return the same value as TimeZone, but it should be more efficient.

We keep a table of DST offsets to prevent calling localtime() on each 
call of this function. This saves a LOT of time on many unixes.

Updated by Paul Eggert <[e-mail]>
********************************************************************/
static int TimeZoneFaster(time_t t)
{
  static struct dst_table {time_t start,end; int zone;} *dst_table = NULL;
  static int table_size = 0;
  int i;
  int zone = 0;

  if (t == 0) t = time(NULL);

  /* Tunis has a 8 day DST region, we need to be careful ... */
#define MAX_DST_WIDTH (365*24*60*60)
#define MAX_DST_SKIP (7*24*60*60)

  for (i=0;i<table_size;i++)
    if (t >= dst_table[i].start && t <= dst_table[i].end) break;

  if (i<table_size) {
    zone = dst_table[i].zone;
  } else {
    time_t low,high;

    zone = TimeZone(t);
    dst_table = (struct dst_table *)Realloc(dst_table,
					      sizeof(dst_table[0])*(i+1));
    if (!dst_table) {
      table_size = 0;
    } else {
      table_size++;

      dst_table[i].zone = zone; 
      dst_table[i].start = dst_table[i].end = t;
    
      /* no entry will cover more than 6 months */
      low = t - MAX_DST_WIDTH/2;
      if (t < low)
	low = TIME_T_MIN;
      
      high = t + MAX_DST_WIDTH/2;
      if (high < t)
	high = TIME_T_MAX;
      
      /* widen the new entry using two bisection searches */
      while (low+60*60 < dst_table[i].start) {
	if (dst_table[i].start - low > MAX_DST_SKIP*2)
	  t = dst_table[i].start - MAX_DST_SKIP;
	else
	  t = low + (dst_table[i].start-low)/2;
	if (TimeZone(t) == zone)
	  dst_table[i].start = t;
	else
	  low = t;
      }

      while (high-60*60 > dst_table[i].end) {
	if (high - dst_table[i].end > MAX_DST_SKIP*2)
	  t = dst_table[i].end + MAX_DST_SKIP;
	else
	  t = high - (high-dst_table[i].end)/2;
	if (TimeZone(t) == zone)
	  dst_table[i].end = t;
	else
	  high = t;
      }
#if 0
      DEBUG(1,("Added DST entry from %s ",
	       asctime(localtime(&dst_table[i].start))));
      DEBUG(1,("to %s (%d)\n",asctime(localtime(&dst_table[i].end)),
	       dst_table[i].zone));
#endif
    }
  }
  return zone;
}

/****************************************************************************
  return the UTC offset in seconds west of UTC, adjusted for extra time offset
  **************************************************************************/
int TimeDiff(time_t t)
{
  return TimeZoneFaster(t) + 60*extra_time_offset;
}


/****************************************************************************
  return the UTC offset in seconds west of UTC, adjusted for extra time
  offset, for a local time value.  If ut = lt + LocTimeDiff(lt), then
  lt = ut - TimeDiff(ut), but the converse does not necessarily hold near
  daylight savings transitions because some local times are ambiguous.
  LocTimeDiff(t) equals TimeDiff(t) except near daylight savings transitions.
  +**************************************************************************/
static int LocTimeDiff(time_t lte)
{
  time_t lt = lte - 60*extra_time_offset;
  int d = TimeZoneFaster(lt);
  time_t t = lt + d;

  /* if overflow occurred, ignore all the adjustments so far */
  if (((lte < lt) ^ (extra_time_offset < 0))  |  ((t < lt) ^ (d < 0)))
    t = lte;

  /* now t should be close enough to the true UTC to yield the right answer */
  return TimeDiff(t);
}


/****************************************************************************
try to optimise the localtime call, it can be quite expensive on some machines
****************************************************************************/
struct tm *LocalTime(time_t *t)
{
  time_t t2 = *t;

  t2 -= TimeDiff(t2);

  return(gmtime(&t2));
}

#define TIME_FIXUP_CONSTANT (369.0*365.25*24*60*60-(3.0*24*60*60+6.0*60*60))

/****************************************************************************
interpret an 8 byte "filetime" structure to a time_t
It's originally in "100ns units since jan 1st 1601"

It appears to be kludge-GMT (at least for file listings). This means
its the GMT you get by taking a localtime and adding the
serverzone. This is NOT the same as GMT in some cases. This routine
converts this to real GMT.
****************************************************************************/
time_t nt_time_to_unix(NTTIME *nt)
{
  double d;
  time_t ret;
  /* The next two lines are a fix needed for the 
     broken SCO compiler. JRA. */
  time_t l_time_min = TIME_T_MIN;
  time_t l_time_max = TIME_T_MAX;

  if (nt->high == 0) return(0);

  d = ((double)nt->high)*4.0*(double)(1<<30);
  d += (nt->low&0xFFF00000);
  d *= 1.0e-7;
 
  /* now adjust by 369 years to make the secs since 1970 */
  d -= TIME_FIXUP_CONSTANT;

  if (!(l_time_min <= d && d <= l_time_max))
    return(0);

  ret = (time_t)(d+0.5);

  /* this takes us from kludge-GMT to real GMT */
  ret -= serverzone;
  ret += LocTimeDiff(ret);