tzset.c

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/*
 * Copyright (C) 2001-2003 by egnite Software GmbH. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holders nor the names of
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY EGNITE SOFTWARE GMBH AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL EGNITE
 * SOFTWARE GMBH OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
 * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * For additional information see http://www.ethernut.de/
 *
 * Portions of the following functions are derived from material which is 
 * Copyright (c) 1985 by Microsoft Corporation.  All rights are reserved.
 */
/*
 * $Log$
 * Revision 1.3  2008/08/11 06:59:41  haraldkipp
 * BSD types replaced by stdint types (feature request #1282721).
 *
 * Revision 1.2  2003/12/19 22:26:38  drsung
 * Dox written.
 *
 * Revision 1.1  2003/11/24 18:07:37  drsung
 * first release
 *
 *
 */

#include <stdint.h>

#include <time.h>
#include "ctime.h"

typedef struct {
    int yr;                     /* year of interest */
    int yd;                     /* day of year */
    long ms;                    /* milli-seconds in the day */
} transitiondate;

/*
 * DST start and end structs.
 */
static transitiondate dststart = { -1, 0, 0L };
static transitiondate dstend = { -1, 0, 0L };
int _daylight = 1;                   /* daylight saving default enabled */
long _dstbias = -1 * 60L * 60L;         /* bias for daylight saving in seconds */
long _timezone = 5L * 60L * 60L;        /* default time zone is EST = -05:00:00 */

/*
 * The macro below is valid for years between 1901 and 2099, which easily
 * includes all years representable by the current implementation of time_t.
 */
#define IS_LEAP_YEAR(year)  ( (year & 3) == 0 )
#define DAY_MILLISEC    (24L * 60L * 60L * 1000L)


static void cvtdate(int trantype,
                    int datetype, int year, int month, int week, int dayofweek, int date, int hour, int min, int sec, int msec)
{
    int yearday;
    int monthdow;

    if (datetype == 1) {

        /*
         * Transition day specified in day-in-month format.
         */

        /*
         * Figure the year-day of the start of the month.
         */
        yearday = 1 + (IS_LEAP_YEAR(year) ? _lpdays[month - 1] : _days[month - 1]);

        /*
         * Figure the day of the week of the start of the month.
         */
        monthdow = (yearday + ((year - 70) * 365) + ((year - 1) >> 2) - _LEAP_YEAR_ADJUST + _BASE_DOW) % 7;

        /*
         * Figure the year-day of the transition date
         */
        if (monthdow <= dayofweek)
            yearday += (dayofweek - monthdow) + (week - 1) * 7;
        else
            yearday += (dayofweek - monthdow) + week * 7;

        /*
         * May have to adjust the calculation above if week == 5 (meaning
         * the last instance of the day in the month). Check if year falls
         * beyond after month and adjust accordingly.
         */
        if ((week == 5) && (yearday > (IS_LEAP_YEAR(year) ? _lpdays[month] : _days[month]))) {
            yearday -= 7;
        }
    } else {
        /*
         * Transition day specified as an absolute day
         */
        yearday = IS_LEAP_YEAR(year) ? _lpdays[month - 1] : _days[month - 1];

        yearday += date;
    }

    if (trantype == 1) {
        /*
         * Converted date was for the start of DST
         */
        dststart.yd = yearday;
        dststart.ms = (long) msec + (1000L * (sec + 60L * (min + 60L * hour)));
        /*
         * Set year field of dststart so that unnecessary calls to
         * cvtdate() may be avoided.
         */
        dststart.yr = year;
    } else {
        /*
         * Converted date was for the end of DST
         */
        dstend.yd = yearday;
        dstend.ms = (long) msec + (1000L * (sec + 60L * (min + 60L * hour)));
        /*
         * The converted date is still a DST date. Must convert to a
         * standard (local) date while being careful the millisecond field
         * does not overflow or underflow.
         */
        if ((dstend.ms += (_dstbias * 1000L)) < 0) {
            dstend.ms += DAY_MILLISEC;
            dstend.yd--;
        } else if (dstend.ms >= DAY_MILLISEC) {
            dstend.ms -= DAY_MILLISEC;
            dstend.yd++;
        }

        /*
         * Set year field of dstend so that unnecessary calls to cvtdate()
         * may be avoided.
         */
        dstend.yr = year;
    }

    return;
}


int _isindst(tm * tb)
{
    long ms;
    if (_daylight == 0)
        return 0;

    /*
     * Compute (recompute) the transition dates for daylight saving time
     * if necessary.The yr (year) fields of dststart and dstend is
     * compared to the year of interest to determine necessity.
     */
    if ((tb->tm_year != dststart.yr) || (tb->tm_year != dstend.yr)) {

        cvtdate(1, 1, tb->tm_year, 3,   /* March */
                5,              /* last... */
                0,              /* ...Sunday */
                0, 2,           /* 02:00 (2 AM) */
                0, 0, 0);

        cvtdate(0, 1, tb->tm_year, 10,  /* October */
                5,              /* last... */
                0,              /* ...Sunday */
                0, 2,           /* 02:00 (2 AM) */
                0, 0, 0);
    }

    /*
     * Handle simple cases first.
     */
    if (dststart.yd < dstend.yd) {
        /*
         * Northern hemisphere ordering
         */
        if ((tb->tm_yday < dststart.yd) || (tb->tm_yday > dstend.yd))
            return 0;
        if ((tb->tm_yday > dststart.yd) && (tb->tm_yday < dstend.yd))
            return 1;
    } else {
        /*
         * Southern hemisphere ordering
         */
        if ((tb->tm_yday < dstend.yd) || (tb->tm_yday > dststart.yd))
            return 1;
        if ((tb->tm_yday > dstend.yd) && (tb->tm_yday < dststart.yd))
            return 0;
    }

    ms = 1000L * (tb->tm_sec + 60L * tb->tm_min + 3600L * tb->tm_hour);

    if (tb->tm_yday == dststart.yd) {
        if (ms >= dststart.ms)
            return 1;
        else
            return 0;
    } else {
        if (ms < dstend.ms)
            return 1;
        else
            return 0;
    }

}