1 // SPDX-License-Identifier: LGPL-2.0+ 1 // SPDX-License-Identifier: LGPL-2.0+
2 /* 2 /*
3 * Copyright (C) 1993, 1994, 1995, 1996, 1997 3 * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
4 * This file is part of the GNU C Library. 4 * This file is part of the GNU C Library.
5 * Contributed by Paul Eggert (eggert@twinsun. 5 * Contributed by Paul Eggert (eggert@twinsun.com).
6 * 6 *
7 * The GNU C Library is free software; you can 7 * The GNU C Library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Librar 8 * modify it under the terms of the GNU Library General Public License as
9 * published by the Free Software Foundation; 9 * published by the Free Software Foundation; either version 2 of the
10 * License, or (at your option) any later vers 10 * License, or (at your option) any later version.
11 * 11 *
12 * The GNU C Library is distributed in the hop 12 * The GNU C Library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Library General Public License for more det 15 * Library General Public License for more details.
16 * 16 *
17 * You should have received a copy of the GNU 17 * You should have received a copy of the GNU Library General Public
18 * License along with the GNU C Library; see t 18 * License along with the GNU C Library; see the file COPYING.LIB. If not,
19 * write to the Free Software Foundation, Inc. 19 * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
20 * Boston, MA 02111-1307, USA. 20 * Boston, MA 02111-1307, USA.
21 */ 21 */
22 22
23 /* 23 /*
24 * Converts the calendar time to broken-down t 24 * Converts the calendar time to broken-down time representation
>> 25 * Based on code from glibc-2.6
25 * 26 *
26 * 2009-7-14: 27 * 2009-7-14:
27 * Moved from glibc-2.6 to kernel by Zhaolei 28 * Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com>
28 * 2021-06-02: <<
29 * Reimplemented by Cassio Neri <cassio.neri <<
30 */ 29 */
31 30
32 #include <linux/time.h> 31 #include <linux/time.h>
33 #include <linux/module.h> 32 #include <linux/module.h>
34 #include <linux/kernel.h> !! 33
>> 34 /*
>> 35 * Nonzero if YEAR is a leap year (every 4 years,
>> 36 * except every 100th isn't, and every 400th is).
>> 37 */
>> 38 static int __isleap(long year)
>> 39 {
>> 40 return (year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0);
>> 41 }
>> 42
>> 43 /* do a mathdiv for long type */
>> 44 static long math_div(long a, long b)
>> 45 {
>> 46 return a / b - (a % b < 0);
>> 47 }
>> 48
>> 49 /* How many leap years between y1 and y2, y1 must less or equal to y2 */
>> 50 static long leaps_between(long y1, long y2)
>> 51 {
>> 52 long leaps1 = math_div(y1 - 1, 4) - math_div(y1 - 1, 100)
>> 53 + math_div(y1 - 1, 400);
>> 54 long leaps2 = math_div(y2 - 1, 4) - math_div(y2 - 1, 100)
>> 55 + math_div(y2 - 1, 400);
>> 56 return leaps2 - leaps1;
>> 57 }
>> 58
>> 59 /* How many days come before each month (0-12). */
>> 60 static const unsigned short __mon_yday[2][13] = {
>> 61 /* Normal years. */
>> 62 {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
>> 63 /* Leap years. */
>> 64 {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366}
>> 65 };
35 66
36 #define SECS_PER_HOUR (60 * 60) 67 #define SECS_PER_HOUR (60 * 60)
37 #define SECS_PER_DAY (SECS_PER_HOUR * 24) 68 #define SECS_PER_DAY (SECS_PER_HOUR * 24)
38 69
39 /** 70 /**
40 * time64_to_tm - converts the calendar time t 71 * time64_to_tm - converts the calendar time to local broken-down time
41 * 72 *
42 * @totalsecs: the number of seconds elapsed !! 73 * @totalsecs the number of seconds elapsed since 00:00:00 on January 1, 1970,
43 * Coordinated Universal Time (UT 74 * Coordinated Universal Time (UTC).
44 * @offset: offset seconds adding to total !! 75 * @offset offset seconds adding to totalsecs.
45 * @result: pointer to struct tm variable !! 76 * @result pointer to struct tm variable to receive broken-down time
46 */ 77 */
47 void time64_to_tm(time64_t totalsecs, int offs 78 void time64_to_tm(time64_t totalsecs, int offset, struct tm *result)
48 { 79 {
49 u32 u32tmp, day_of_century, year_of_ce !! 80 long days, rem, y;
50 u64 u64tmp, udays, century, year; <<
51 bool is_Jan_or_Feb, is_leap_year; <<
52 long days, rem; <<
53 int remainder; 81 int remainder;
>> 82 const unsigned short *ip;
54 83
55 days = div_s64_rem(totalsecs, SECS_PER 84 days = div_s64_rem(totalsecs, SECS_PER_DAY, &remainder);
56 rem = remainder; 85 rem = remainder;
57 rem += offset; 86 rem += offset;
58 while (rem < 0) { 87 while (rem < 0) {
59 rem += SECS_PER_DAY; 88 rem += SECS_PER_DAY;
60 --days; 89 --days;
61 } 90 }
62 while (rem >= SECS_PER_DAY) { 91 while (rem >= SECS_PER_DAY) {
63 rem -= SECS_PER_DAY; 92 rem -= SECS_PER_DAY;
64 ++days; 93 ++days;
65 } 94 }
66 95
67 result->tm_hour = rem / SECS_PER_HOUR; 96 result->tm_hour = rem / SECS_PER_HOUR;
68 rem %= SECS_PER_HOUR; 97 rem %= SECS_PER_HOUR;
69 result->tm_min = rem / 60; 98 result->tm_min = rem / 60;
70 result->tm_sec = rem % 60; 99 result->tm_sec = rem % 60;
71 100
72 /* January 1, 1970 was a Thursday. */ 101 /* January 1, 1970 was a Thursday. */
73 result->tm_wday = (4 + days) % 7; 102 result->tm_wday = (4 + days) % 7;
74 if (result->tm_wday < 0) 103 if (result->tm_wday < 0)
75 result->tm_wday += 7; 104 result->tm_wday += 7;
76 105
77 /* !! 106 y = 1970;
78 * The following algorithm is, basical !! 107
79 * and Schneider [1]. In a few words: !! 108 while (days < 0 || days >= (__isleap(y) ? 366 : 365)) {
80 * (fictitious) calendar where the yea !! 109 /* Guess a corrected year, assuming 365 days per year. */
81 * (*), and finishes in February, mont !! 110 long yg = y + math_div(days, 365);
82 * mathematically convenient because t !! 111
83 * depend on whether the year is leap !! 112 /* Adjust DAYS and Y to match the guessed year. */
84 * !! 113 days -= (yg - y) * 365 + leaps_between(y, yg);
85 * March 1st 0-th day of th !! 114 y = yg;
86 * ... !! 115 }
87 * April 1st 31-st day of t !! 116
88 * ... !! 117 result->tm_year = y - 1900;
89 * January 1st 306-th day of !! 118
90 * ... !! 119 result->tm_yday = days;
91 * February 28th 364-th day of !! 120
92 * February 29th 365-th day of !! 121 ip = __mon_yday[__isleap(y)];
93 * !! 122 for (y = 11; days < ip[y]; y--)
94 * After having worked out the date in !! 123 continue;
95 * (using just arithmetics) it's easy !! 124 days -= ip[y];
96 * corresponding date in the Gregorian !! 125
97 * !! 126 result->tm_mon = y;
98 * [1] "Euclidean Affine Functions and !! 127 result->tm_mday = days + 1;
99 * Algorithms". https://arxiv.org/abs/ <<
100 * <<
101 * (*) The numbering of months follows <<
102 * is slightly different from [1]. <<
103 */ <<
104 <<
105 udays = ((u64) days) + 2305843009213 <<
106 <<
107 u64tmp = 4 * udays + 3; <<
108 century = div64_u64_rem(u64tmp <<
109 day_of_century = (u32) (u64tmp / 4); <<
110 <<
111 u32tmp = 4 * day_of_century + <<
112 u64tmp = 2939745ULL * u32tmp; <<
113 year_of_century = upper_32_bits(u64tmp <<
114 day_of_year = lower_32_bits(u64tmp <<
115 <<
116 year = 100 * century + year <<
117 is_leap_year = year_of_century ? !( <<
118 <<
119 u32tmp = 2141 * day_of_year + <<
120 month = u32tmp >> 16; <<
121 day = ((u16) u32tmp) / 214 <<
122 <<
123 /* <<
124 * Recall that January 1st is the 306- <<
125 * computational (not Gregorian) calen <<
126 */ <<
127 is_Jan_or_Feb = day_of_year >= 306; <<
128 <<
129 /* Convert to the Gregorian calendar a <<
130 year = year + is_Jan_or_Feb <<
131 month = is_Jan_or_Feb ? mont <<
132 day = day + 1; <<
133 day_of_year += is_Jan_or_Feb ? -30 <<
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 } 128 }
141 EXPORT_SYMBOL(time64_to_tm); 129 EXPORT_SYMBOL(time64_to_tm);
142 130
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