1/*	$OpenBSD: clock_subr.c,v 1.6 2016/08/26 07:09:56 guenther Exp $	*/
2/*	$NetBSD: clock_subr.c,v 1.3 1997/03/15 18:11:16 is Exp $	*/
3
4/*
5 * Copyright (c) 1988 University of Utah.
6 * Copyright (c) 1982, 1990, 1993
7 *	The Regents of the University of California.  All rights reserved.
8 *
9 * This code is derived from software contributed to Berkeley by
10 * the Systems Programming Group of the University of Utah Computer
11 * Science Department.
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 * 1. Redistributions of source code must retain the above copyright
17 *    notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 *    notice, this list of conditions and the following disclaimer in the
20 *    documentation and/or other materials provided with the distribution.
21 * 3. Neither the name of the University nor the names of its contributors
22 *    may be used to endorse or promote products derived from this software
23 *    without specific prior written permission.
24 *
25 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * SUCH DAMAGE.
36 *
37 * from: Utah $Hdr: clock.c 1.18 91/01/21$
38 *
39 *	@(#)clock.c	8.2 (Berkeley) 1/12/94
40 */
41
42/*
43 * Generic routines to convert between a POSIX date
44 * (seconds since 1/1/1970) and yr/mo/day/hr/min/sec
45 * Derived from arch/hp300/hp300/clock.c
46 */
47
48#include <sys/types.h>
49#include <sys/time.h>
50#include <sys/systm.h>
51
52static inline int leapyear(int year);
53#define FEBRUARY	2
54#define	days_in_year(a) 	(leapyear(a) ? 366 : 365)
55#define	days_in_month(a) 	(month_days[(a) - 1])
56
57static const int month_days[12] = {
58	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
59};
60
61/*
62 * This inline avoids some unnecessary modulo operations
63 * as compared with the usual macro:
64 *   ( ((year % 4) == 0 &&
65 *      (year % 100) != 0) ||
66 *     ((year % 400) == 0) )
67 * It is otherwise equivalent.
68 */
69static inline int
70leapyear(int year)
71{
72	int rv = 0;
73
74	if ((year & 3) == 0) {
75		rv = 1;
76		if ((year % 100) == 0) {
77			rv = 0;
78			if ((year % 400) == 0)
79				rv = 1;
80		}
81	}
82	return (rv);
83}
84
85time_t
86clock_ymdhms_to_secs(struct clock_ymdhms *dt)
87{
88	time_t secs;
89	int i, year, days;
90
91	year = dt->dt_year;
92
93	/*
94	 * Compute days since start of time.
95	 * First from years, then from months.
96	 */
97	days = 0;
98	for (i = POSIX_BASE_YEAR; i < year; i++)
99		days += days_in_year(i);
100	if (leapyear(year) && dt->dt_mon > FEBRUARY)
101		days++;
102
103	/* Months */
104	for (i = 1; i < dt->dt_mon; i++)
105	  	days += days_in_month(i);
106	days += (dt->dt_day - 1);
107
108	/* Add hours, minutes, seconds. */
109	secs = (time_t)((days
110	    * 24 + dt->dt_hour)
111	    * 60 + dt->dt_min)
112	    * 60 + dt->dt_sec;
113
114	return (secs);
115}
116
117/* This function uses a copy of month_days[] */
118#undef	days_in_month
119#define	days_in_month(a) 	(mthdays[(a) - 1])
120
121void
122clock_secs_to_ymdhms(time_t secs, struct clock_ymdhms *dt)
123{
124	int mthdays[12];
125	int i, days;
126	int rsec;	/* remainder seconds */
127
128	memcpy(mthdays, month_days, sizeof(mthdays));
129
130	days = secs / SECDAY;
131	rsec = secs % SECDAY;
132
133	/* Day of week (Note: 1/1/1970 was a Thursday) */
134	dt->dt_wday = (days + 4) % 7;
135
136	/* Subtract out whole years, counting them in i. */
137	for (i = POSIX_BASE_YEAR; days >= days_in_year(i); i++)
138		days -= days_in_year(i);
139	dt->dt_year = i;
140
141	/* Subtract out whole months, counting them in i. */
142	if (leapyear(i))
143		days_in_month(FEBRUARY) = 29;
144	for (i = 1; days >= days_in_month(i); i++)
145		days -= days_in_month(i);
146	dt->dt_mon = i;
147
148	/* Days are what is left over (+1) from all that. */
149	dt->dt_day = days + 1;
150
151	/* Hours, minutes, seconds are easy */
152	dt->dt_hour = rsec / 3600;
153	rsec = rsec % 3600;
154	dt->dt_min  = rsec / 60;
155	rsec = rsec % 60;
156	dt->dt_sec  = rsec;
157}
158