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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
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27  */
28 
29 /* $Id: eu_dst.h 2338 2013-04-07 16:13:35Z swfltek $ */
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 < 1)
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 < 1)
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:95
unsigned char uint8_t
Definition: stdint.h:80
#define ONE_HOUR
Definition: time.h:418
Definition: time.h:159
uint32_t time_t
Definition: time.h:116
void gmtime_r(const time_t *timer, struct tm *timeptr)
Definition: gmtime_r.c:38

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