xref: /titanic_51/usr/src/lib/libast/common/tm/tmequiv.c (revision 78b2cb9a814f49b9599bf830034a12338259e0c9)
1 /***********************************************************************
2 *                                                                      *
3 *               This software is part of the ast package               *
4 *           Copyright (c) 1985-2007 AT&T Knowledge Ventures            *
5 *                      and is licensed under the                       *
6 *                  Common Public License, Version 1.0                  *
7 *                      by AT&T Knowledge Ventures                      *
8 *                                                                      *
9 *                A copy of the License is available at                 *
10 *            http://www.opensource.org/licenses/cpl1.0.txt             *
11 *         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
12 *                                                                      *
13 *              Information and Software Systems Research               *
14 *                            AT&T Research                             *
15 *                           Florham Park NJ                            *
16 *                                                                      *
17 *                 Glenn Fowler <gsf@research.att.com>                  *
18 *                  David Korn <dgk@research.att.com>                   *
19 *                   Phong Vo <kpv@research.att.com>                    *
20 *                                                                      *
21 ***********************************************************************/
22 #pragma prototyped
23 /*
24  * Glenn Fowler
25  * AT&T Research
26  *
27  * time_t conversion support
28  */
29 
30 #include <tm.h>
31 
32 /*
33  * use one of the 14 equivalent calendar years to determine
34  * daylight savings time for future years beyond the range
35  * of the local system (via tmxmake())
36  */
37 
38 static const short equiv[] =
39 {
40 	2006, 2012,
41 	2001, 2024,
42 	2002, 2008,
43 	2003, 2020,
44 	2009, 2004,
45 	2010, 2016,
46 	2005, 2000,
47 };
48 
49 /*
50  * return the circa 2000 equivalent calendar year for tm
51  */
52 
53 int
54 tmequiv(Tm_t* tm)
55 {
56 	return tm->tm_year < (2038 - 1900) ? (tm->tm_year + 1900) : equiv[tm->tm_wday + tmisleapyear(tm->tm_year)];
57 }
58