cedtoxtime.c

/***
* cedtoxtime.c - convert OS local time to time_t
*
*       Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       defines __loctotime_t() - convert OS local time to internal format
*       (time_t).
*
*******************************************************************************/

#include <celib.h>
#include <time.h>

/***
*time_t __loctotime_t(yr, mo, dy, hr, mn, sc, dstflag) - converts OS local
*       time to internal time format (i.e., a time_t value)
*
*Purpose:
*       Converts a local time value, obtained in a broken down format from
*       the host OS, to time_t format (i.e., the number elapsed seconds since
*       01-01-70, 00:00:00, UTC).
*
*Entry:
*       int yr, mo, dy -    date
*       int hr, mn, sc -    time
*       int dstflag    -    1 if Daylight Time, 0 if Standard Time, -1 if
*                           not specified.
*
*Exit:
*       Returns calendar time value.
*
*Exceptions:
*
*******************************************************************************/

time_t 
__loctotime_t (
        int yr,         /* 0 based */
        int mo,         /* 1 based */
        int dy,         /* 1 based */
        int hr,
        int mn,
        int sc,
        int dstflag )
{
  int tmpdays;
  long tmptim;
  struct tm tb;

  /*
   * Do a quick range check on the year and convert it to a delta
   * off of 1900.
   */
  if ( ((long)(yr -= 1900) < _BASE_YEAR) || ((long)yr > _MAX_YEAR) )
    return (time_t)(-1);

  /*
   * Compute the number of elapsed days in the current year. Note the
   * test for a leap year would fail in the year 2100, if this was in
   * range (which it isn't).
   */
  tmpdays = dy + _days[mo - 1];
  if ( !(yr & 3) && (mo > 2) )
    tmpdays++;

  /*
   * Compute the number of elapsed seconds since the Epoch. Note the
   * computation of elapsed leap years would break down after 2100
   * if such values were in range (fortunately, they aren't).
   */
  tmptim = /* 365 days for each year */
    (((long)yr - _BASE_YEAR) * 365L

     /* one day for each elapsed leap year */
     + (long)((yr - 1) >> 2) - _LEAP_YEAR_ADJUST

     /* number of elapsed days in yr */
     + tmpdays)

    /* convert to hours and add in hr */
    * 24L + hr;

  tmptim = /* convert to minutes and add in mn */
    (tmptim * 60L + mn)

    /* convert to seconds and add in sec */
    * 60L + sc;
  /*
   * Account for time zone.
   */
  __tzset();
  tmptim += _timezone;

  /*
   * Fill in enough fields of tb for _isindst(), then call it to
   * determine DST.
   */
  tb.tm_yday = tmpdays;
  tb.tm_year = yr;
  tb.tm_mon  = mo - 1;
  tb.tm_hour = hr;
  if ( (dstflag == 1) || ((dstflag == -1) && _daylight &&
			  _isindst(&tb)) )
    tmptim += _dstbias;
  return(tmptim);
}