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usa_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: usa__dst_8h_source.html,v 1.1.1.2 2016/02/09 07:13:44 joerg_wunsch Exp $ */
30 
31 /**
32  Daylight Saving function for the USA. To utilize this function, you must
33  \code #include <util/usa_dst.h> \endcode
34  and
35  \code set_dst(usa_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 
53 #ifndef USA_DST_H
54 #define USA_DST_H
55 
56 #ifdef __cplusplus
57 extern "C" {
58 #endif
59 
60 #include <time.h>
61 #include <inttypes.h>
62 
63 #ifndef DST_START_MONTH
64 #define DST_START_MONTH MARCH
65 #endif
66 
67 #ifndef DST_END_MONTH
68 #define DST_END_MONTH NOVEMBER
69 #endif
70 
71 #ifndef DST_START_WEEK
72 #define DST_START_WEEK 2
73 #endif
74 
75 #ifndef DST_END_WEEK
76 #define DST_END_WEEK 1
77 #endif
78 
79  int usa_dst(const time_t * timer, int32_t * z) {
80  time_t t;
81  struct tm tmptr;
82  uint8_t month, week, hour, day_of_week, d;
83  int n;
84 
85  /* obtain the variables */
86  t = *timer + *z;
87  gmtime_r(&t, &tmptr);
88  month = tmptr.tm_mon;
89  day_of_week = tmptr.tm_wday;
90  week = week_of_month(&tmptr, 0);
91  hour = tmptr.tm_hour;
92 
93  if ((month > DST_START_MONTH) && (month < DST_END_MONTH))
94  return ONE_HOUR;
95 
96  if (month < DST_START_MONTH)
97  return 0;
98  if (month > DST_END_MONTH)
99  return 0;
100 
101  if (month == DST_START_MONTH) {
102 
103  if (week < DST_START_WEEK)
104  return 0;
105  if (week > DST_START_WEEK)
106  return ONE_HOUR;
107 
108  if (day_of_week > SUNDAY)
109  return ONE_HOUR;
110  if (hour >= 2)
111  return ONE_HOUR;
112  return 0;
113  }
114  if (week > DST_END_WEEK)
115  return 0;
116  if (week < DST_END_WEEK)
117  return ONE_HOUR;
118  if (day_of_week > SUNDAY)
119  return 0;
120  if (hour >= 1)
121  return 0;
122  return ONE_HOUR;
123 
124  }
125 
126 #ifdef __cplusplus
127 }
128 #endif
129 
130 #endif
uint8_t week_of_month(const struct tm *timeptr, uint8_t start)
Definition: week_of_month.c:42
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