135728b82SThomas Gleixner // SPDX-License-Identifier: LGPL-2.0+
257f1f087SZhaolei /*
357f1f087SZhaolei * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
457f1f087SZhaolei * This file is part of the GNU C Library.
557f1f087SZhaolei * Contributed by Paul Eggert (eggert@twinsun.com).
657f1f087SZhaolei *
757f1f087SZhaolei * The GNU C Library is free software; you can redistribute it and/or
857f1f087SZhaolei * modify it under the terms of the GNU Library General Public License as
957f1f087SZhaolei * published by the Free Software Foundation; either version 2 of the
1057f1f087SZhaolei * License, or (at your option) any later version.
1157f1f087SZhaolei *
1257f1f087SZhaolei * The GNU C Library is distributed in the hope that it will be useful,
1357f1f087SZhaolei * but WITHOUT ANY WARRANTY; without even the implied warranty of
1457f1f087SZhaolei * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
1557f1f087SZhaolei * Library General Public License for more details.
1657f1f087SZhaolei *
1757f1f087SZhaolei * You should have received a copy of the GNU Library General Public
1857f1f087SZhaolei * License along with the GNU C Library; see the file COPYING.LIB. If not,
1957f1f087SZhaolei * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
2057f1f087SZhaolei * Boston, MA 02111-1307, USA.
2157f1f087SZhaolei */
2257f1f087SZhaolei
2357f1f087SZhaolei /*
2457f1f087SZhaolei * Converts the calendar time to broken-down time representation
2557f1f087SZhaolei *
2657f1f087SZhaolei * 2009-7-14:
2757f1f087SZhaolei * Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com>
28*27601055SCassio Neri * 2021-06-02:
29*27601055SCassio Neri * Reimplemented by Cassio Neri <cassio.neri@gmail.com>
3057f1f087SZhaolei */
3157f1f087SZhaolei
3257f1f087SZhaolei #include <linux/time.h>
3357f1f087SZhaolei #include <linux/module.h>
34*27601055SCassio Neri #include <linux/kernel.h>
3557f1f087SZhaolei
3657f1f087SZhaolei #define SECS_PER_HOUR (60 * 60)
3757f1f087SZhaolei #define SECS_PER_DAY (SECS_PER_HOUR * 24)
3857f1f087SZhaolei
3957f1f087SZhaolei /**
40e6c2682aSDeepa Dinamani * time64_to_tm - converts the calendar time to local broken-down time
4157f1f087SZhaolei *
42a0f5a65fSAlex Shi * @totalsecs: the number of seconds elapsed since 00:00:00 on January 1, 1970,
4357f1f087SZhaolei * Coordinated Universal Time (UTC).
44a0f5a65fSAlex Shi * @offset: offset seconds adding to totalsecs.
45a0f5a65fSAlex Shi * @result: pointer to struct tm variable to receive broken-down time
4657f1f087SZhaolei */
time64_to_tm(time64_t totalsecs,int offset,struct tm * result)47e6c2682aSDeepa Dinamani void time64_to_tm(time64_t totalsecs, int offset, struct tm *result)
4857f1f087SZhaolei {
49*27601055SCassio Neri u32 u32tmp, day_of_century, year_of_century, day_of_year, month, day;
50*27601055SCassio Neri u64 u64tmp, udays, century, year;
51*27601055SCassio Neri bool is_Jan_or_Feb, is_leap_year;
52*27601055SCassio Neri long days, rem;
53e6c2682aSDeepa Dinamani int remainder;
5457f1f087SZhaolei
55e6c2682aSDeepa Dinamani days = div_s64_rem(totalsecs, SECS_PER_DAY, &remainder);
56e6c2682aSDeepa Dinamani rem = remainder;
5757f1f087SZhaolei rem += offset;
5857f1f087SZhaolei while (rem < 0) {
5957f1f087SZhaolei rem += SECS_PER_DAY;
6057f1f087SZhaolei --days;
6157f1f087SZhaolei }
6257f1f087SZhaolei while (rem >= SECS_PER_DAY) {
6357f1f087SZhaolei rem -= SECS_PER_DAY;
6457f1f087SZhaolei ++days;
6557f1f087SZhaolei }
6657f1f087SZhaolei
6757f1f087SZhaolei result->tm_hour = rem / SECS_PER_HOUR;
6857f1f087SZhaolei rem %= SECS_PER_HOUR;
6957f1f087SZhaolei result->tm_min = rem / 60;
7057f1f087SZhaolei result->tm_sec = rem % 60;
7157f1f087SZhaolei
7257f1f087SZhaolei /* January 1, 1970 was a Thursday. */
7357f1f087SZhaolei result->tm_wday = (4 + days) % 7;
7457f1f087SZhaolei if (result->tm_wday < 0)
7557f1f087SZhaolei result->tm_wday += 7;
7657f1f087SZhaolei
77*27601055SCassio Neri /*
78*27601055SCassio Neri * The following algorithm is, basically, Proposition 6.3 of Neri
79*27601055SCassio Neri * and Schneider [1]. In a few words: it works on the computational
80*27601055SCassio Neri * (fictitious) calendar where the year starts in March, month = 2
81*27601055SCassio Neri * (*), and finishes in February, month = 13. This calendar is
82*27601055SCassio Neri * mathematically convenient because the day of the year does not
83*27601055SCassio Neri * depend on whether the year is leap or not. For instance:
84*27601055SCassio Neri *
85*27601055SCassio Neri * March 1st 0-th day of the year;
86*27601055SCassio Neri * ...
87*27601055SCassio Neri * April 1st 31-st day of the year;
88*27601055SCassio Neri * ...
89*27601055SCassio Neri * January 1st 306-th day of the year; (Important!)
90*27601055SCassio Neri * ...
91*27601055SCassio Neri * February 28th 364-th day of the year;
92*27601055SCassio Neri * February 29th 365-th day of the year (if it exists).
93*27601055SCassio Neri *
94*27601055SCassio Neri * After having worked out the date in the computational calendar
95*27601055SCassio Neri * (using just arithmetics) it's easy to convert it to the
96*27601055SCassio Neri * corresponding date in the Gregorian calendar.
97*27601055SCassio Neri *
98*27601055SCassio Neri * [1] "Euclidean Affine Functions and Applications to Calendar
99*27601055SCassio Neri * Algorithms". https://arxiv.org/abs/2102.06959
100*27601055SCassio Neri *
101*27601055SCassio Neri * (*) The numbering of months follows tm more closely and thus,
102*27601055SCassio Neri * is slightly different from [1].
103*27601055SCassio Neri */
10457f1f087SZhaolei
105*27601055SCassio Neri udays = ((u64) days) + 2305843009213814918ULL;
10657f1f087SZhaolei
107*27601055SCassio Neri u64tmp = 4 * udays + 3;
108*27601055SCassio Neri century = div64_u64_rem(u64tmp, 146097, &u64tmp);
109*27601055SCassio Neri day_of_century = (u32) (u64tmp / 4);
11057f1f087SZhaolei
111*27601055SCassio Neri u32tmp = 4 * day_of_century + 3;
112*27601055SCassio Neri u64tmp = 2939745ULL * u32tmp;
113*27601055SCassio Neri year_of_century = upper_32_bits(u64tmp);
114*27601055SCassio Neri day_of_year = lower_32_bits(u64tmp) / 2939745 / 4;
11557f1f087SZhaolei
116*27601055SCassio Neri year = 100 * century + year_of_century;
117*27601055SCassio Neri is_leap_year = year_of_century ? !(year_of_century % 4) : !(century % 4);
11857f1f087SZhaolei
119*27601055SCassio Neri u32tmp = 2141 * day_of_year + 132377;
120*27601055SCassio Neri month = u32tmp >> 16;
121*27601055SCassio Neri day = ((u16) u32tmp) / 2141;
12257f1f087SZhaolei
123*27601055SCassio Neri /*
124*27601055SCassio Neri * Recall that January 1st is the 306-th day of the year in the
125*27601055SCassio Neri * computational (not Gregorian) calendar.
126*27601055SCassio Neri */
127*27601055SCassio Neri is_Jan_or_Feb = day_of_year >= 306;
128*27601055SCassio Neri
129*27601055SCassio Neri /* Convert to the Gregorian calendar and adjust to Unix time. */
130*27601055SCassio Neri year = year + is_Jan_or_Feb - 6313183731940000ULL;
131*27601055SCassio Neri month = is_Jan_or_Feb ? month - 12 : month;
132*27601055SCassio Neri day = day + 1;
133*27601055SCassio Neri day_of_year += is_Jan_or_Feb ? -306 : 31 + 28 + is_leap_year;
134*27601055SCassio Neri
135*27601055SCassio Neri /* Convert to tm's format. */
136*27601055SCassio Neri result->tm_year = (long) (year - 1900);
137*27601055SCassio Neri result->tm_mon = (int) month;
138*27601055SCassio Neri result->tm_mday = (int) day;
139*27601055SCassio Neri result->tm_yday = (int) day_of_year;
14057f1f087SZhaolei }
141e6c2682aSDeepa Dinamani EXPORT_SYMBOL(time64_to_tm);
142