gmt2local.c

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/*
 * Copyright (c) 1997
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that: (1) source code distributions
 * retain the above copyright notice and this paragraph in its entirety, (2)
 * distributions including binary code include the above copyright notice and
 * this paragraph in its entirety in the documentation or other materials
 * provided with the distribution, and (3) all advertising materials mentioning
 * features or use of this software display the following acknowledgement:
 * ``This product includes software developed by the University of California,
 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
 * the University nor the names of its contributors may be used to endorse
 * or promote products derived from this software without specific prior
 * written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

#include <stdlib.h> 
#include <time.h>

/*
 * Returns the difference between gmt and local time in seconds.
 * Use gmtime() and localtime() to keep things simple.
 */
int32_t gmt2local(time_t t)
{
        register int dt, dir;
        register struct tm *gmt, *loc;
        struct tm sgmt;

        if (t == 0)
                t = time(NULL);
        gmt = &sgmt;
        *gmt = *gmtime(&t);
        loc = localtime(&t);
        dt = (loc->tm_hour - gmt->tm_hour) * 60 * 60 +
            (loc->tm_min - gmt->tm_min) * 60;

        /*
         * If the year or julian day is different, we span 00:00 GMT
         * and must add or subtract a day. Check the year first to
         * avoid problems when the julian day wraps.
         */
        dir = loc->tm_year - gmt->tm_year;
        if (dir == 0)
                dir = loc->tm_yday - gmt->tm_yday;
        dt += dir * 24 * 60 * 60;

        return (dt);
}

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