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eu_dst.h
00001 /*
00002  * (c)2012 Michael Duane Rice All rights reserved.
00003  *
00004  * Redistribution and use in source and binary forms, with or without
00005  * modification, are permitted provided that the following conditions are
00006  * met:
00007  *
00008  * Redistributions of source code must retain the above copyright notice, this
00009  * list of conditions and the following disclaimer. Redistributions in binary
00010  * form must reproduce the above copyright notice, this list of conditions
00011  * and the following disclaimer in the documentation and/or other materials
00012  * provided with the distribution. Neither the name of the copyright holders
00013  * nor the names of contributors may be used to endorse or promote products
00014  * derived from this software without specific prior written permission.
00015  *
00016  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
00017  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
00018  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
00019  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
00020  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
00021  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
00022  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
00023  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
00024  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
00025  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
00026  * POSSIBILITY OF SUCH DAMAGE.
00027  */
00028 
00029 /* $Id: eu_dst.h 2492 2015-10-27 09:07:56Z swfltek $ */
00030 
00031 /**
00032     Daylight Saving function for the European Union. To utilize this function, you must
00033     \code #include <util/eu_dst.h> \endcode
00034     and
00035     \code set_dst(eu_dst); \endcode
00036 
00037     Given the time stamp and time zone parameters provided, the Daylight Saving function must
00038     return a value appropriate for the tm structures' tm_isdst element. That is...
00039 
00040     0 : If Daylight Saving is not in effect.
00041 
00042     -1 : If it cannot be determined if Daylight Saving is in effect.
00043 
00044     A positive integer : Represents the number of seconds a clock is advanced for Daylight Saving.
00045     This will typically be ONE_HOUR.
00046 
00047     Daylight Saving 'rules' are subject to frequent change. For production applications it is
00048     recommended to write your own DST function, which uses 'rules' obtained from, and modifiable by,
00049     the end user ( perhaps stored in EEPROM ).
00050 */
00051 
00052 #ifndef EU_DST_H
00053 #define EU_DST_H
00054 
00055 #ifdef __cplusplus
00056 extern          "C" {
00057 #endif
00058 
00059 #include <time.h>
00060 #include <inttypes.h>
00061 
00062     int             eu_dst(const time_t * timer, int32_t * z) {
00063         struct tm       tmptr;
00064         uint8_t         month, mday, hour, day_of_week, d;
00065         int             n;
00066 
00067         /* obtain the variables */
00068                         gmtime_r(timer, &tmptr);
00069                         month = tmptr.tm_mon;
00070                         day_of_week = tmptr.tm_wday;
00071                         mday = tmptr.tm_mday - 1;
00072                         hour = tmptr.tm_hour;
00073 
00074         if              ((month > MARCH) && (month < OCTOBER))
00075                             return ONE_HOUR;
00076 
00077         if              (month < MARCH)
00078                             return 0;
00079         if              (month > OCTOBER)
00080                             return 0;
00081 
00082         /* determine mday of last Sunday */
00083                         n = tmptr.tm_mday - 1;
00084                         n -= day_of_week;
00085                         n += 7;
00086                         d = n % 7;  /* date of first Sunday */
00087 
00088                         n = 31 - d;
00089                         n /= 7; /* number of Sundays left in the month */
00090 
00091                         d = d + 7 * n;  /* mday of final Sunday */
00092 
00093         if              (month == MARCH) {
00094             if (d < mday)
00095                 return 0;
00096             if (d > mday)
00097                 return ONE_HOUR;
00098             if (hour < 2)
00099                 return 0;
00100             return ONE_HOUR;
00101         }
00102         if              (d < mday)
00103                             return ONE_HOUR;
00104         if              (d > mday)
00105                             return 0;
00106         if              (hour < 2)
00107                             return ONE_HOUR;
00108                         return 0;
00109 
00110     }
00111 
00112 #ifdef __cplusplus
00113 }
00114 #endif
00115 
00116 #endif
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