mbed_mktime.c

00001 /* mbed Microcontroller Library
00002  * Copyright (c) 2017-2017 ARM Limited
00003  *
00004  * Licensed under the Apache License, Version 2.0 (the "License");
00005  * you may not use this file except in compliance with the License.
00006  * You may obtain a copy of the License at
00007  *
00008  *     http://www.apache.org/licenses/LICENSE-2.0
00009  *
00010  * Unless required by applicable law or agreed to in writing, software
00011  * distributed under the License is distributed on an "AS IS" BASIS,
00012  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00013  * See the License for the specific language governing permissions and
00014  * limitations under the License.
00015  */
00016 
00017 #include "mbed_mktime.h"
00018 
00019 /*
00020  * time constants 
00021  */
00022 #define SECONDS_BY_MINUTES 60
00023 #define MINUTES_BY_HOUR 60
00024 #define SECONDS_BY_HOUR (SECONDS_BY_MINUTES * MINUTES_BY_HOUR)
00025 #define HOURS_BY_DAY 24 
00026 #define SECONDS_BY_DAY (SECONDS_BY_HOUR * HOURS_BY_DAY)
00027 
00028 /*
00029  * 2 dimensional array containing the number of seconds elapsed before a given 
00030  * month.
00031  * The second index map to the month while the first map to the type of year:
00032  *   - 0: non leap year 
00033  *   - 1: leap year
00034  */
00035 static const uint32_t seconds_before_month[2][12] = {
00036     {
00037         0,
00038         31 * SECONDS_BY_DAY,
00039         (31 + 28) * SECONDS_BY_DAY,
00040         (31 + 28 + 31) * SECONDS_BY_DAY,
00041         (31 + 28 + 31 + 30) * SECONDS_BY_DAY,
00042         (31 + 28 + 31 + 30 + 31) * SECONDS_BY_DAY,
00043         (31 + 28 + 31 + 30 + 31 + 30) * SECONDS_BY_DAY,
00044         (31 + 28 + 31 + 30 + 31 + 30 + 31) * SECONDS_BY_DAY,
00045         (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31) * SECONDS_BY_DAY,
00046         (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30) * SECONDS_BY_DAY,
00047         (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31) * SECONDS_BY_DAY,
00048         (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30) * SECONDS_BY_DAY,
00049     },
00050     {
00051         0,
00052         31 * SECONDS_BY_DAY,
00053         (31 + 29) * SECONDS_BY_DAY,
00054         (31 + 29 + 31) * SECONDS_BY_DAY,
00055         (31 + 29 + 31 + 30) * SECONDS_BY_DAY,
00056         (31 + 29 + 31 + 30 + 31) * SECONDS_BY_DAY,
00057         (31 + 29 + 31 + 30 + 31 + 30) * SECONDS_BY_DAY,
00058         (31 + 29 + 31 + 30 + 31 + 30 + 31) * SECONDS_BY_DAY,
00059         (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31) * SECONDS_BY_DAY,
00060         (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30) * SECONDS_BY_DAY,
00061         (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31) * SECONDS_BY_DAY,
00062         (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30) * SECONDS_BY_DAY,
00063     }
00064 };
00065 
00066 bool _rtc_is_leap_year(int year) {
00067     /* 
00068      * since in practice, the value manipulated by this algorithm lie in the 
00069      * range [70 : 138], the algorith can be reduced to: year % 4.
00070      * The algorithm valid over the full range of value is: 
00071 
00072         year = 1900 + year;
00073         if (year % 4) {
00074             return false;
00075         } else if (year % 100) {
00076             return true;
00077         } else if (year % 400) {
00078             return false;
00079         }
00080         return true;
00081 
00082      */ 
00083     return (year) % 4 ? false : true;
00084 }
00085 
00086 time_t _rtc_mktime(const struct tm* time) {
00087     // partial check for the upper bound of the range
00088     // normalization might happen at the end of the function 
00089     // this solution is faster than checking if the input is after the 19th of 
00090     // january 2038 at 03:14:07.  
00091     if ((time->tm_year < 70) || (time->tm_year > 138)) { 
00092         return ((time_t) -1);
00093     }
00094 
00095     uint32_t result = time->tm_sec;
00096     result += time->tm_min * SECONDS_BY_MINUTES;
00097     result += time->tm_hour * SECONDS_BY_HOUR;
00098     result += (time->tm_mday - 1) * SECONDS_BY_DAY;
00099     result += seconds_before_month[_rtc_is_leap_year(time->tm_year)][time->tm_mon];
00100 
00101     if (time->tm_year > 70) { 
00102         // valid in the range [70:138] 
00103         uint32_t count_of_leap_days = ((time->tm_year - 1) / 4) - (70 / 4);
00104         result += (((time->tm_year - 70) * 365) + count_of_leap_days) * SECONDS_BY_DAY;
00105     }
00106 
00107     if (result > INT32_MAX) { 
00108         return (time_t) -1;
00109     }
00110 
00111     return result;
00112 }
00113 
00114 bool _rtc_localtime(time_t timestamp, struct tm* time_info) {
00115     if (((int32_t) timestamp) < 0) { 
00116         return false;
00117     } 
00118 
00119     time_info->tm_sec = timestamp % 60;
00120     timestamp = timestamp / 60;   // timestamp in minutes
00121     time_info->tm_min = timestamp % 60;
00122     timestamp = timestamp / 60;  // timestamp in hours
00123     time_info->tm_hour = timestamp % 24;
00124     timestamp = timestamp / 24;  // timestamp in days;
00125 
00126     // compute the weekday
00127     // The 1st of January 1970 was a Thursday which is equal to 4 in the weekday
00128     // representation ranging from [0:6]
00129     time_info->tm_wday = (timestamp + 4) % 7;
00130 
00131     // years start at 70
00132     time_info->tm_year = 70;
00133     while (true) { 
00134         if (_rtc_is_leap_year(time_info->tm_year) && timestamp >= 366) {
00135             ++time_info->tm_year;
00136             timestamp -= 366;
00137         } else if (!_rtc_is_leap_year(time_info->tm_year) && timestamp >= 365) {
00138             ++time_info->tm_year;
00139             timestamp -= 365;
00140         } else {
00141             // the remaining days are less than a years
00142             break;
00143         }
00144     }
00145 
00146     time_info->tm_yday = timestamp;
00147 
00148     // convert days into seconds and find the current month
00149     timestamp *= SECONDS_BY_DAY;
00150     time_info->tm_mon = 11;
00151     bool leap = _rtc_is_leap_year(time_info->tm_year);
00152     for (uint32_t i = 0; i < 12; ++i) {
00153         if ((uint32_t) timestamp < seconds_before_month[leap][i]) {
00154             time_info->tm_mon = i - 1;
00155             break;
00156         }
00157     }
00158 
00159     // remove month from timestamp and compute the number of days.
00160     // note: unlike other fields, days are not 0 indexed.
00161     timestamp -= seconds_before_month[leap][time_info->tm_mon];
00162     time_info->tm_mday = (timestamp / SECONDS_BY_DAY) + 1;
00163 
00164     return true;
00165 }