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eu_dst.h
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: eu__dst_8h_source.html,v 1.1.1.2 2016/02/09 07:13:36 joerg_wunsch Exp $ */
30 
31 /**
32  Daylight Saving function for the European Union. To utilize this function, you must
33  \code #include <util/eu_dst.h> \endcode
34  and
35  \code set_dst(eu_dst); \endcode
36 
37  Given the time stamp and time zone parameters provided, the Daylight Saving function must
38  return a value appropriate for the tm structures' tm_isdst element. That is...
39 
40  0 : If Daylight Saving is not in effect.
41 
42  -1 : If it cannot be determined if Daylight Saving is in effect.
43 
44  A positive integer : Represents the number of seconds a clock is advanced for Daylight Saving.
45  This will typically be ONE_HOUR.
46 
47  Daylight Saving 'rules' are subject to frequent change. For production applications it is
48  recommended to write your own DST function, which uses 'rules' obtained from, and modifiable by,
49  the end user ( perhaps stored in EEPROM ).
50 */
51 
52 #ifndef EU_DST_H
53 #define EU_DST_H
54 
55 #ifdef __cplusplus
56 extern "C" {
57 #endif
58 
59 #include <time.h>
60 #include <inttypes.h>
61 
62  int eu_dst(const time_t * timer, int32_t * z) {
63  struct tm tmptr;
64  uint8_t month, mday, hour, day_of_week, d;
65  int n;
66 
67  /* obtain the variables */
68  gmtime_r(timer, &tmptr);
69  month = tmptr.tm_mon;
70  day_of_week = tmptr.tm_wday;
71  mday = tmptr.tm_mday - 1;
72  hour = tmptr.tm_hour;
73 
74  if ((month > MARCH) && (month < OCTOBER))
75  return ONE_HOUR;
76 
77  if (month < MARCH)
78  return 0;
79  if (month > OCTOBER)
80  return 0;
81 
82  /* determine mday of last Sunday */
83  n = tmptr.tm_mday - 1;
84  n -= day_of_week;
85  n += 7;
86  d = n % 7; /* date of first Sunday */
87 
88  n = 31 - d;
89  n /= 7; /* number of Sundays left in the month */
90 
91  d = d + 7 * n; /* mday of final Sunday */
92 
93  if (month == MARCH) {
94  if (d < mday)
95  return 0;
96  if (d > mday)
97  return ONE_HOUR;
98  if (hour < 2)
99  return 0;
100  return ONE_HOUR;
101  }
102  if (d < mday)
103  return ONE_HOUR;
104  if (d > mday)
105  return 0;
106  if (hour < 2)
107  return ONE_HOUR;
108  return 0;
109 
110  }
111 
112 #ifdef __cplusplus
113 }
114 #endif
115 
116 #endif
signed long int int32_t
Definition: stdint.h:98
unsigned char uint8_t
Definition: stdint.h:83
#define ONE_HOUR
Definition: time.h:404
Definition: time.h:144
uint32_t time_t
Definition: time.h:116
void gmtime_r(const time_t *timer, struct tm *timeptr)
Definition: gmtime_r.c:38