1 /*
2 * (C)2012 Michael Duane Rice All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions are
6 * met:
7 *
8 * Redistributions of source code must retain the above copyright notice, this
9 * list of conditions and the following disclaimer. Redistributions in binary
10 * form must reproduce the above copyright notice, this list of conditions
11 * and the following disclaimer in the documentation and/or other materials
12 * provided with the distribution. Neither the name of the copyright holders
13 * nor the names of contributors may be used to endorse or promote products
14 * derived from this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
17 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
20 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
24 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
26 * POSSIBILITY OF SUCH DAMAGE.
27 */
28
29 /* $Id: mk_gmtime.c 2369 2013-04-28 14:19:35Z swfltek $ */
30
31 /*
32 'Break down' a y2k time stamp into the elements of struct tm.
33 Unlike mktime(), this function does not 'normalize' the elements of timeptr.
34
35 */
36
37 #include <time.h>
38
39 time_t
mk_gmtime(const struct tm * timeptr)40 mk_gmtime(const struct tm * timeptr)
41 {
42
43 time_t ret;
44 uint32_t tmp;
45 int n, m, d, leaps;
46
47 /*
48 Determine elapsed whole days since the epoch to the beginning of this year. Since our epoch is
49 at a conjunction of the leap cycles, we can do this rather quickly.
50 */
51 n = timeptr->tm_year - 100;
52 leaps = 0;
53 if (n) {
54 m = n - 1;
55 leaps = m / 4;
56 leaps -= m / 100;
57 leaps++;
58 }
59 tmp = 365UL * n + leaps;
60
61 /*
62 Derive the day of year from month and day of month. We use the pattern of 31 day months
63 followed by 30 day months to our advantage, but we must 'special case' Jan/Feb, and
64 account for a 'phase change' between July and August (153 days after March 1).
65 */
66 d = timeptr->tm_mday - 1; /* tm_mday is one based */
67
68 /* handle Jan/Feb as a special case */
69 if (timeptr->tm_mon < 2) {
70 if (timeptr->tm_mon)
71 d += 31;
72
73 } else {
74 n = 59 + is_leap_year(timeptr->tm_year + 1900);
75 d += n;
76 n = timeptr->tm_mon - MARCH;
77
78 /* account for phase change */
79 if (n > (JULY - MARCH))
80 d += 153;
81 n %= 5;
82
83 /*
84 * n is now an index into a group of alternating 31 and 30
85 * day months... 61 day pairs.
86 */
87 m = n / 2;
88 m *= 61;
89 d += m;
90
91 /*
92 * if n is odd, we are in the second half of the
93 * month pair
94 */
95 if (n & 1)
96 d += 31;
97 }
98
99 /* Add day of year to elapsed days, and convert to seconds */
100 tmp += d;
101 tmp *= ONE_DAY;
102 ret = tmp;
103
104 /* compute 'fractional' day */
105 tmp = timeptr->tm_hour;
106 tmp *= ONE_HOUR;
107 tmp += timeptr->tm_min * 60UL;
108 tmp += timeptr->tm_sec;
109
110 ret += tmp;
111
112 return ret;
113 }
114