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35728b82 | 1 | // SPDX-License-Identifier: LGPL-2.0+ |
57f1f087 Z |
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 | |
57f1f087 Z |
25 | * |
26 | * 2009-7-14: | |
27 | * Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com> | |
27601055 CN |
28 | * 2021-06-02: |
29 | * Reimplemented by Cassio Neri <cassio.neri@gmail.com> | |
57f1f087 Z |
30 | */ |
31 | ||
32 | #include <linux/time.h> | |
33 | #include <linux/module.h> | |
27601055 | 34 | #include <linux/kernel.h> |
57f1f087 Z |
35 | |
36 | #define SECS_PER_HOUR (60 * 60) | |
37 | #define SECS_PER_DAY (SECS_PER_HOUR * 24) | |
38 | ||
39 | /** | |
e6c2682a | 40 | * time64_to_tm - converts the calendar time to local broken-down time |
57f1f087 | 41 | * |
a0f5a65f | 42 | * @totalsecs: the number of seconds elapsed since 00:00:00 on January 1, 1970, |
57f1f087 | 43 | * Coordinated Universal Time (UTC). |
a0f5a65f AS |
44 | * @offset: offset seconds adding to totalsecs. |
45 | * @result: pointer to struct tm variable to receive broken-down time | |
57f1f087 | 46 | */ |
e6c2682a | 47 | void time64_to_tm(time64_t totalsecs, int offset, struct tm *result) |
57f1f087 | 48 | { |
27601055 CN |
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; | |
e6c2682a | 53 | int remainder; |
57f1f087 | 54 | |
e6c2682a DD |
55 | days = div_s64_rem(totalsecs, SECS_PER_DAY, &remainder); |
56 | rem = remainder; | |
57f1f087 Z |
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 | ||
27601055 CN |
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; | |
57f1f087 | 140 | } |
e6c2682a | 141 | EXPORT_SYMBOL(time64_to_tm); |