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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
gmt2local(time_t 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