1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * rtc and date/time utility functions 4 * 5 * Copyright (C) 2005-06 Tower Technologies 6 * Author: Alessandro Zummo <a.zummo@towertech.it> 7 * 8 * based on arch/arm/common/rtctime.c and other bits 9 * 10 * Author: Cassio Neri <cassio.neri@gmail.com> (rtc_time64_to_tm) 11 */ 12 13 #include <linux/export.h> 14 #include <linux/rtc.h> 15 16 static const unsigned char rtc_days_in_month[] = { 17 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 18 }; 19 20 static const unsigned short rtc_ydays[2][13] = { 21 /* Normal years */ 22 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 }, 23 /* Leap years */ 24 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 } 25 }; 26 27 /* 28 * The number of days in the month. 29 */ 30 int rtc_month_days(unsigned int month, unsigned int year) 31 { 32 return rtc_days_in_month[month] + (is_leap_year(year) && month == 1); 33 } 34 EXPORT_SYMBOL(rtc_month_days); 35 36 /* 37 * The number of days since January 1. (0 to 365) 38 */ 39 int rtc_year_days(unsigned int day, unsigned int month, unsigned int year) 40 { 41 return rtc_ydays[is_leap_year(year)][month] + day - 1; 42 } 43 EXPORT_SYMBOL(rtc_year_days); 44 45 /** 46 * rtc_time64_to_tm - converts time64_t to rtc_time. 47 * 48 * @time: The number of seconds since 01-01-1970 00:00:00. 49 * Works for values since at least 1900 50 * @tm: Pointer to the struct rtc_time. 51 */ 52 void rtc_time64_to_tm(time64_t time, struct rtc_time *tm) 53 { 54 int secs; 55 56 u64 u64tmp; 57 u32 u32tmp, udays, century, day_of_century, year_of_century, year, 58 day_of_year, month, day; 59 bool is_Jan_or_Feb, is_leap_year; 60 61 /* 62 * The time represented by `time` is given in seconds since 1970-01-01 63 * (UTC). As the division done below might misbehave for negative 64 * values, we convert it to seconds since 0000-03-01 and then assume it 65 * will be non-negative. 66 * Below we do 4 * udays + 3 which should fit into a 32 bit unsigned 67 * variable. So the latest date this algorithm works for is 1073741823 68 * days after 0000-03-01 which is in the year 2939805. 69 */ 70 time += (u64)719468 * 86400; 71 72 udays = div_s64_rem(time, 86400, &secs); 73 74 /* 75 * day of the week, 0000-03-01 was a Wednesday (in the proleptic 76 * Gregorian calendar) 77 */ 78 tm->tm_wday = (udays + 3) % 7; 79 80 /* 81 * The following algorithm is, basically, Figure 12 of Neri 82 * and Schneider [1]. In a few words: it works on the computational 83 * (fictitious) calendar where the year starts in March, month = 2 84 * (*), and finishes in February, month = 13. This calendar is 85 * mathematically convenient because the day of the year does not 86 * depend on whether the year is leap or not. For instance: 87 * 88 * March 1st 0-th day of the year; 89 * ... 90 * April 1st 31-st day of the year; 91 * ... 92 * January 1st 306-th day of the year; (Important!) 93 * ... 94 * February 28th 364-th day of the year; 95 * February 29th 365-th day of the year (if it exists). 96 * 97 * After having worked out the date in the computational calendar 98 * (using just arithmetics) it's easy to convert it to the 99 * corresponding date in the Gregorian calendar. 100 * 101 * [1] Neri C, Schneider L. Euclidean affine functions and their 102 * application to calendar algorithms. Softw Pract Exper. 103 * 2023;53(4):937-970. doi: 10.1002/spe.3172 104 * https://doi.org/10.1002/spe.3172 105 * 106 * (*) The numbering of months follows rtc_time more closely and 107 * thus, is slightly different from [1]. 108 */ 109 110 u32tmp = 4 * udays + 3; 111 century = u32tmp / 146097; 112 day_of_century = u32tmp % 146097 / 4; 113 114 u32tmp = 4 * day_of_century + 3; 115 u64tmp = 2939745ULL * u32tmp; 116 year_of_century = upper_32_bits(u64tmp); 117 day_of_year = lower_32_bits(u64tmp) / 2939745 / 4; 118 119 year = 100 * century + year_of_century; 120 is_leap_year = year_of_century != 0 ? 121 year_of_century % 4 == 0 : century % 4 == 0; 122 123 u32tmp = 2141 * day_of_year + 132377; 124 month = u32tmp >> 16; 125 day = ((u16) u32tmp) / 2141; 126 127 /* 128 * Recall that January 01 is the 306-th day of the year in the 129 * computational (not Gregorian) calendar. 130 */ 131 is_Jan_or_Feb = day_of_year >= 306; 132 133 /* Converts to the Gregorian calendar. */ 134 year = year + is_Jan_or_Feb; 135 month = is_Jan_or_Feb ? month - 12 : month; 136 day = day + 1; 137 138 day_of_year = is_Jan_or_Feb ? 139 day_of_year - 306 : day_of_year + 31 + 28 + is_leap_year; 140 141 /* Converts to rtc_time's format. */ 142 tm->tm_year = (int) (year - 1900); 143 tm->tm_mon = (int) month; 144 tm->tm_mday = (int) day; 145 tm->tm_yday = (int) day_of_year + 1; 146 147 tm->tm_hour = secs / 3600; 148 secs -= tm->tm_hour * 3600; 149 tm->tm_min = secs / 60; 150 tm->tm_sec = secs - tm->tm_min * 60; 151 152 tm->tm_isdst = 0; 153 } 154 EXPORT_SYMBOL(rtc_time64_to_tm); 155 156 /* 157 * Does the rtc_time represent a valid date/time? 158 */ 159 int rtc_valid_tm(struct rtc_time *tm) 160 { 161 if (tm->tm_year < 70 || 162 tm->tm_year > (INT_MAX - 1900) || 163 ((unsigned int)tm->tm_mon) >= 12 || 164 tm->tm_mday < 1 || 165 tm->tm_mday > rtc_month_days(tm->tm_mon, 166 ((unsigned int)tm->tm_year + 1900)) || 167 ((unsigned int)tm->tm_hour) >= 24 || 168 ((unsigned int)tm->tm_min) >= 60 || 169 ((unsigned int)tm->tm_sec) >= 60) 170 return -EINVAL; 171 172 return 0; 173 } 174 EXPORT_SYMBOL(rtc_valid_tm); 175 176 /* 177 * rtc_tm_to_time64 - Converts rtc_time to time64_t. 178 * Convert Gregorian date to seconds since 01-01-1970 00:00:00. 179 */ 180 time64_t rtc_tm_to_time64(struct rtc_time *tm) 181 { 182 return mktime64(((unsigned int)tm->tm_year + 1900), tm->tm_mon + 1, 183 tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec); 184 } 185 EXPORT_SYMBOL(rtc_tm_to_time64); 186 187 /* 188 * Convert rtc_time to ktime 189 */ 190 ktime_t rtc_tm_to_ktime(struct rtc_time tm) 191 { 192 return ktime_set(rtc_tm_to_time64(&tm), 0); 193 } 194 EXPORT_SYMBOL_GPL(rtc_tm_to_ktime); 195 196 /* 197 * Convert ktime to rtc_time 198 */ 199 struct rtc_time rtc_ktime_to_tm(ktime_t kt) 200 { 201 struct timespec64 ts; 202 struct rtc_time ret; 203 204 ts = ktime_to_timespec64(kt); 205 /* Round up any ns */ 206 if (ts.tv_nsec) 207 ts.tv_sec++; 208 rtc_time64_to_tm(ts.tv_sec, &ret); 209 return ret; 210 } 211 EXPORT_SYMBOL_GPL(rtc_ktime_to_tm); 212