Diff: platform/mbed_mktime.c

Revision:

0:bdf663c61a82

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/platform/mbed_mktime.c	Tue Jun 14 09:21:18 2022 +0000
@@ -0,0 +1,166 @@
+/* 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 (time_t) -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;
+}
+