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      1 /*
      2  * Copyright (c) 1997
      3  *	The Regents of the University of California.  All rights reserved.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that: (1) source code distributions
      7  * retain the above copyright notice and this paragraph in its entirety, (2)
      8  * distributions including binary code include the above copyright notice and
      9  * this paragraph in its entirety in the documentation or other materials
     10  * provided with the distribution, and (3) all advertising materials mentioning
     11  * features or use of this software display the following acknowledgement:
     12  * ``This product includes software developed by the University of California,
     13  * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
     14  * the University nor the names of its contributors may be used to endorse
     15  * or promote products derived from this software without specific prior
     16  * written permission.
     17  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
     18  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
     19  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
     20  */
     21 
     22 #ifdef HAVE_CONFIG_H
     23 #include "config.h"
     24 #endif
     25 
     26 #include <netdissect-stdinc.h>
     27 
     28 #include <stdio.h>
     29 
     30 #ifdef HAVE_OS_PROTO_H
     31 #include "os-proto.h"
     32 #endif
     33 
     34 #include "gmt2local.h"
     35 
     36 /*
     37  * Returns the difference between gmt and local time in seconds.
     38  * Use gmtime() and localtime() to keep things simple.
     39  */
     40 int32_t
     41 gmt2local(time_t t)
     42 {
     43 	register int dt, dir;
     44 	register struct tm *gmt, *loc;
     45 	struct tm sgmt;
     46 
     47 	if (t == 0)
     48 		t = time(NULL);
     49 	gmt = &sgmt;
     50 	*gmt = *gmtime(&t);
     51 	loc = localtime(&t);
     52 	dt = (loc->tm_hour - gmt->tm_hour) * 60 * 60 +
     53 	    (loc->tm_min - gmt->tm_min) * 60;
     54 
     55 	/*
     56 	 * If the year or julian day is different, we span 00:00 GMT
     57 	 * and must add or subtract a day. Check the year first to
     58 	 * avoid problems when the julian day wraps.
     59 	 */
     60 	dir = loc->tm_year - gmt->tm_year;
     61 	if (dir == 0)
     62 		dir = loc->tm_yday - gmt->tm_yday;
     63 	dt += dir * 24 * 60 * 60;
     64 
     65 	return (dt);
     66 }
     67