gmt2local.c revision 39297 
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#ifndef lint
23static const char rcsid[] =
24    "@(#) $Header: gmt2local.c,v 1.2 97/01/23 22:31:25 leres Exp $ (LBL)";
25#endif
26
27#include <sys/types.h>
28#include <sys/time.h>
29
30#include <stdio.h>
31#ifdef TIME_WITH_SYS_TIME
32#include <time.h>
33#endif
34
35#include "gnuc.h"
36#ifdef HAVE_OS_PROTO_H
37#include "os-proto.h"
38#endif
39
40#include "gmt2local.h"
41
42/*
43 * Returns the difference between gmt and local time in seconds.
44 * Use gmtime() and localtime() to keep things simple.
45 */
46int32_t
47gmt2local(time_t t)
48{
49	register int dt, dir;
50	register struct tm *gmt, *loc;
51	struct tm sgmt;
52
53	if (t == 0)
54		t = time(NULL);
55	gmt = &sgmt;
56	*gmt = *gmtime(&t);
57	loc = localtime(&t);
58	dt = (loc->tm_hour - gmt->tm_hour) * 60 * 60 +
59	    (loc->tm_min - gmt->tm_min) * 60;
60
61	/*
62	 * If the year or julian day is different, we span 00:00 GMT
63	 * and must add or subtract a day. Check the year first to
64	 * avoid problems when the julian day wraps.
65	 */
66	dir = loc->tm_year - gmt->tm_year;
67	if (dir == 0)
68		dir = loc->tm_yday - gmt->tm_yday;
69	dt += dir * 24 * 60 * 60;
70
71	return (dt);
72}
73