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Diff: platform/mbed_mktime.c
- Revision:
- 167:e84263d55307
- Child:
- 169:e3b6fe271b81
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/platform/mbed_mktime.c Wed Jun 21 17:46:44 2017 +0100 @@ -0,0 +1,165 @@ +/* mbed Microcontroller Library + * Copyright (c) 2017-2017 ARM Limited + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +#include "mbed_mktime.h" + +/* + * time constants + */ +#define SECONDS_BY_MINUTES 60 +#define MINUTES_BY_HOUR 60 +#define SECONDS_BY_HOUR (SECONDS_BY_MINUTES * MINUTES_BY_HOUR) +#define HOURS_BY_DAY 24 +#define SECONDS_BY_DAY (SECONDS_BY_HOUR * HOURS_BY_DAY) + +/* + * 2 dimensional array containing the number of seconds elapsed before a given + * month. + * The second index map to the month while the first map to the type of year: + * - 0: non leap year + * - 1: leap year + */ +static const uint32_t seconds_before_month[2][12] = { + { + 0, + 31 * SECONDS_BY_DAY, + (31 + 28) * SECONDS_BY_DAY, + (31 + 28 + 31) * SECONDS_BY_DAY, + (31 + 28 + 31 + 30) * SECONDS_BY_DAY, + (31 + 28 + 31 + 30 + 31) * SECONDS_BY_DAY, + (31 + 28 + 31 + 30 + 31 + 30) * SECONDS_BY_DAY, + (31 + 28 + 31 + 30 + 31 + 30 + 31) * SECONDS_BY_DAY, + (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31) * SECONDS_BY_DAY, + (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30) * SECONDS_BY_DAY, + (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31) * SECONDS_BY_DAY, + (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30) * SECONDS_BY_DAY, + }, + { + 0, + 31 * SECONDS_BY_DAY, + (31 + 29) * SECONDS_BY_DAY, + (31 + 29 + 31) * SECONDS_BY_DAY, + (31 + 29 + 31 + 30) * SECONDS_BY_DAY, + (31 + 29 + 31 + 30 + 31) * SECONDS_BY_DAY, + (31 + 29 + 31 + 30 + 31 + 30) * SECONDS_BY_DAY, + (31 + 29 + 31 + 30 + 31 + 30 + 31) * SECONDS_BY_DAY, + (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31) * SECONDS_BY_DAY, + (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30) * SECONDS_BY_DAY, + (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31) * SECONDS_BY_DAY, + (31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30) * SECONDS_BY_DAY, + } +}; + +bool _rtc_is_leap_year(int year) { + /* + * since in practice, the value manipulated by this algorithm lie in the + * range [70 : 138], the algorith can be reduced to: year % 4. + * The algorithm valid over the full range of value is: + + year = 1900 + year; + if (year % 4) { + return false; + } else if (year % 100) { + return true; + } else if (year % 400) { + return false; + } + return true; + + */ + return (year) % 4 ? false : true; +} + +time_t _rtc_mktime(const struct tm* time) { + // partial check for the upper bound of the range + // normalization might happen at the end of the function + // this solution is faster than checking if the input is after the 19th of + // january 2038 at 03:14:07. + if ((time->tm_year < 70) || (time->tm_year > 138)) { + return ((time_t) -1); + } + + uint32_t result = time->tm_sec; + result += time->tm_min * SECONDS_BY_MINUTES; + result += time->tm_hour * SECONDS_BY_HOUR; + result += (time->tm_mday - 1) * SECONDS_BY_DAY; + result += seconds_before_month[_rtc_is_leap_year(time->tm_year)][time->tm_mon]; + + if (time->tm_year > 70) { + // valid in the range [70:138] + uint32_t count_of_leap_days = ((time->tm_year - 1) / 4) - (70 / 4); + result += (((time->tm_year - 70) * 365) + count_of_leap_days) * SECONDS_BY_DAY; + } + + if (result > INT32_MAX) { + return -1; + } + + return result; +} + +bool _rtc_localtime(time_t timestamp, struct tm* time_info) { + if (((int32_t) timestamp) < 0) { + return false; + } + + time_info->tm_sec = timestamp % 60; + timestamp = timestamp / 60; // timestamp in minutes + time_info->tm_min = timestamp % 60; + timestamp = timestamp / 60; // timestamp in hours + time_info->tm_hour = timestamp % 24; + timestamp = timestamp / 24; // timestamp in days; + + // compute the weekday + // The 1st of January 1970 was a Thursday which is equal to 4 in the weekday + // representation ranging from [0:6] + time_info->tm_wday = (timestamp + 4) % 7; + + // years start at 70 + time_info->tm_year = 70; + while (true) { + if (_rtc_is_leap_year(time_info->tm_year) && timestamp >= 366) { + ++time_info->tm_year; + timestamp -= 366; + } else if (!_rtc_is_leap_year(time_info->tm_year) && timestamp >= 365) { + ++time_info->tm_year; + timestamp -= 365; + } else { + // the remaining days are less than a years + break; + } + } + + time_info->tm_yday = timestamp; + + // convert days into seconds and find the current month + timestamp *= SECONDS_BY_DAY; + time_info->tm_mon = 11; + bool leap = _rtc_is_leap_year(time_info->tm_year); + for (uint32_t i = 0; i < 12; ++i) { + if ((uint32_t) timestamp < seconds_before_month[leap][i]) { + time_info->tm_mon = i - 1; + break; + } + } + + // remove month from timestamp and compute the number of days. + // note: unlike other fields, days are not 0 indexed. + timestamp -= seconds_before_month[leap][time_info->tm_mon]; + time_info->tm_mday = (timestamp / SECONDS_BY_DAY) + 1; + + return true; +}