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1// SPDX-License-Identifier: LGPL-2.0+
2/*
3 * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
4 * This file is part of the GNU C Library.
5 * Contributed by Paul Eggert (eggert@twinsun.com).
6 *
7 * The GNU C Library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Library General Public License as
9 * published by the Free Software Foundation; either version 2 of the
10 * License, or (at your option) any later version.
11 *
12 * The GNU C Library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Library General Public License for more details.
16 *
17 * You should have received a copy of the GNU Library General Public
18 * License along with the GNU C Library; see the file COPYING.LIB. If not,
19 * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
20 * Boston, MA 02111-1307, USA.
21 */
22
23/*
24 * Converts the calendar time to broken-down time representation
25 *
26 * 2009-7-14:
27 * Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com>
28 * 2021-06-02:
29 * Reimplemented by Cassio Neri <cassio.neri@gmail.com>
30 */
31
32#include <linux/time.h>
33#include <linux/module.h>
34#include <linux/kernel.h>
35
36#define SECS_PER_HOUR (60 * 60)
37#define SECS_PER_DAY (SECS_PER_HOUR * 24)
38
39/**
40 * time64_to_tm - converts the calendar time to local broken-down time
41 *
42 * @totalsecs: the number of seconds elapsed since 00:00:00 on January 1, 1970,
43 * Coordinated Universal Time (UTC).
44 * @offset: offset seconds adding to totalsecs.
45 * @result: pointer to struct tm variable to receive broken-down time
46 */
47void time64_to_tm(time64_t totalsecs, int offset, struct tm *result)
48{
49 u32 u32tmp, day_of_century, year_of_century, day_of_year, month, day;
50 u64 u64tmp, udays, century, year;
51 bool is_Jan_or_Feb, is_leap_year;
52 long days, rem;
53 int remainder;
54
55 days = div_s64_rem(totalsecs, SECS_PER_DAY, &remainder);
56 rem = remainder;
57 rem += offset;
58 while (rem < 0) {
59 rem += SECS_PER_DAY;
60 --days;
61 }
62 while (rem >= SECS_PER_DAY) {
63 rem -= SECS_PER_DAY;
64 ++days;
65 }
66
67 result->tm_hour = rem / SECS_PER_HOUR;
68 rem %= SECS_PER_HOUR;
69 result->tm_min = rem / 60;
70 result->tm_sec = rem % 60;
71
72 /* January 1, 1970 was a Thursday. */
73 result->tm_wday = (4 + days) % 7;
74 if (result->tm_wday < 0)
75 result->tm_wday += 7;
76
77 /*
78 * The following algorithm is, basically, Proposition 6.3 of Neri
79 * and Schneider [1]. In a few words: it works on the computational
80 * (fictitious) calendar where the year starts in March, month = 2
81 * (*), and finishes in February, month = 13. This calendar is
82 * mathematically convenient because the day of the year does not
83 * depend on whether the year is leap or not. For instance:
84 *
85 * March 1st 0-th day of the year;
86 * ...
87 * April 1st 31-st day of the year;
88 * ...
89 * January 1st 306-th day of the year; (Important!)
90 * ...
91 * February 28th 364-th day of the year;
92 * February 29th 365-th day of the year (if it exists).
93 *
94 * After having worked out the date in the computational calendar
95 * (using just arithmetics) it's easy to convert it to the
96 * corresponding date in the Gregorian calendar.
97 *
98 * [1] "Euclidean Affine Functions and Applications to Calendar
99 * Algorithms". https://arxiv.org/abs/2102.06959
100 *
101 * (*) The numbering of months follows tm more closely and thus,
102 * is slightly different from [1].
103 */
104
105 udays = ((u64) days) + 2305843009213814918ULL;
106
107 u64tmp = 4 * udays + 3;
108 century = div64_u64_rem(u64tmp, 146097, &u64tmp);
109 day_of_century = (u32) (u64tmp / 4);
110
111 u32tmp = 4 * day_of_century + 3;
112 u64tmp = 2939745ULL * u32tmp;
113 year_of_century = upper_32_bits(u64tmp);
114 day_of_year = lower_32_bits(u64tmp) / 2939745 / 4;
115
116 year = 100 * century + year_of_century;
117 is_leap_year = year_of_century ? !(year_of_century % 4) : !(century % 4);
118
119 u32tmp = 2141 * day_of_year + 132377;
120 month = u32tmp >> 16;
121 day = ((u16) u32tmp) / 2141;
122
123 /*
124 * Recall that January 1st is the 306-th day of the year in the
125 * computational (not Gregorian) calendar.
126 */
127 is_Jan_or_Feb = day_of_year >= 306;
128
129 /* Convert to the Gregorian calendar and adjust to Unix time. */
130 year = year + is_Jan_or_Feb - 6313183731940000ULL;
131 month = is_Jan_or_Feb ? month - 12 : month;
132 day = day + 1;
133 day_of_year += is_Jan_or_Feb ? -306 : 31 + 28 + is_leap_year;
134
135 /* Convert to tm's format. */
136 result->tm_year = (long) (year - 1900);
137 result->tm_mon = (int) month;
138 result->tm_mday = (int) day;
139 result->tm_yday = (int) day_of_year;
140}
141EXPORT_SYMBOL(time64_to_tm);
1/*
2 * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
3 * This file is part of the GNU C Library.
4 * Contributed by Paul Eggert (eggert@twinsun.com).
5 *
6 * The GNU C Library is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Library General Public License as
8 * published by the Free Software Foundation; either version 2 of the
9 * License, or (at your option) any later version.
10 *
11 * The GNU C Library is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Library General Public License for more details.
15 *
16 * You should have received a copy of the GNU Library General Public
17 * License along with the GNU C Library; see the file COPYING.LIB. If not,
18 * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
19 * Boston, MA 02111-1307, USA.
20 */
21
22/*
23 * Converts the calendar time to broken-down time representation
24 * Based on code from glibc-2.6
25 *
26 * 2009-7-14:
27 * Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com>
28 */
29
30#include <linux/time.h>
31#include <linux/module.h>
32
33/*
34 * Nonzero if YEAR is a leap year (every 4 years,
35 * except every 100th isn't, and every 400th is).
36 */
37static int __isleap(long year)
38{
39 return (year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0);
40}
41
42/* do a mathdiv for long type */
43static long math_div(long a, long b)
44{
45 return a / b - (a % b < 0);
46}
47
48/* How many leap years between y1 and y2, y1 must less or equal to y2 */
49static long leaps_between(long y1, long y2)
50{
51 long leaps1 = math_div(y1 - 1, 4) - math_div(y1 - 1, 100)
52 + math_div(y1 - 1, 400);
53 long leaps2 = math_div(y2 - 1, 4) - math_div(y2 - 1, 100)
54 + math_div(y2 - 1, 400);
55 return leaps2 - leaps1;
56}
57
58/* How many days come before each month (0-12). */
59static const unsigned short __mon_yday[2][13] = {
60 /* Normal years. */
61 {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
62 /* Leap years. */
63 {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366}
64};
65
66#define SECS_PER_HOUR (60 * 60)
67#define SECS_PER_DAY (SECS_PER_HOUR * 24)
68
69/**
70 * time64_to_tm - converts the calendar time to local broken-down time
71 *
72 * @totalsecs the number of seconds elapsed since 00:00:00 on January 1, 1970,
73 * Coordinated Universal Time (UTC).
74 * @offset offset seconds adding to totalsecs.
75 * @result pointer to struct tm variable to receive broken-down time
76 */
77void time64_to_tm(time64_t totalsecs, int offset, struct tm *result)
78{
79 long days, rem, y;
80 int remainder;
81 const unsigned short *ip;
82
83 days = div_s64_rem(totalsecs, SECS_PER_DAY, &remainder);
84 rem = remainder;
85 rem += offset;
86 while (rem < 0) {
87 rem += SECS_PER_DAY;
88 --days;
89 }
90 while (rem >= SECS_PER_DAY) {
91 rem -= SECS_PER_DAY;
92 ++days;
93 }
94
95 result->tm_hour = rem / SECS_PER_HOUR;
96 rem %= SECS_PER_HOUR;
97 result->tm_min = rem / 60;
98 result->tm_sec = rem % 60;
99
100 /* January 1, 1970 was a Thursday. */
101 result->tm_wday = (4 + days) % 7;
102 if (result->tm_wday < 0)
103 result->tm_wday += 7;
104
105 y = 1970;
106
107 while (days < 0 || days >= (__isleap(y) ? 366 : 365)) {
108 /* Guess a corrected year, assuming 365 days per year. */
109 long yg = y + math_div(days, 365);
110
111 /* Adjust DAYS and Y to match the guessed year. */
112 days -= (yg - y) * 365 + leaps_between(y, yg);
113 y = yg;
114 }
115
116 result->tm_year = y - 1900;
117
118 result->tm_yday = days;
119
120 ip = __mon_yday[__isleap(y)];
121 for (y = 11; days < ip[y]; y--)
122 continue;
123 days -= ip[y];
124
125 result->tm_mon = y;
126 result->tm_mday = days + 1;
127}
128EXPORT_SYMBOL(time64_to_tm);