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Diffstat (limited to 'kernel/time/timeconv.c')
| -rw-r--r-- | kernel/time/timeconv.c | 141 |
1 files changed, 141 insertions, 0 deletions
diff --git a/kernel/time/timeconv.c b/kernel/time/timeconv.c new file mode 100644 index 000000000..59b922c82 --- /dev/null +++ b/kernel/time/timeconv.c @@ -0,0 +1,141 @@ +// SPDX-License-Identifier: LGPL-2.0+ +/* + * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc. + * This file is part of the GNU C Library. + * Contributed by Paul Eggert (eggert@twinsun.com). + * + * The GNU C Library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Library General Public License as + * published by the Free Software Foundation; either version 2 of the + * License, or (at your option) any later version. + * + * The GNU C Library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Library General Public License for more details. + * + * You should have received a copy of the GNU Library General Public + * License along with the GNU C Library; see the file COPYING.LIB. If not, + * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, + * Boston, MA 02111-1307, USA. + */ + +/* + * Converts the calendar time to broken-down time representation + * + * 2009-7-14: + * Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com> + * 2021-06-02: + * Reimplemented by Cassio Neri <cassio.neri@gmail.com> + */ + +#include <linux/time.h> +#include <linux/module.h> +#include <linux/kernel.h> + +#define SECS_PER_HOUR (60 * 60) +#define SECS_PER_DAY (SECS_PER_HOUR * 24) + +/** + * time64_to_tm - converts the calendar time to local broken-down time + * + * @totalsecs: the number of seconds elapsed since 00:00:00 on January 1, 1970, + * Coordinated Universal Time (UTC). + * @offset: offset seconds adding to totalsecs. + * @result: pointer to struct tm variable to receive broken-down time + */ +void time64_to_tm(time64_t totalsecs, int offset, struct tm *result) +{ + u32 u32tmp, day_of_century, year_of_century, day_of_year, month, day; + u64 u64tmp, udays, century, year; + bool is_Jan_or_Feb, is_leap_year; + long days, rem; + int remainder; + + days = div_s64_rem(totalsecs, SECS_PER_DAY, &remainder); + rem = remainder; + rem += offset; + while (rem < 0) { + rem += SECS_PER_DAY; + --days; + } + while (rem >= SECS_PER_DAY) { + rem -= SECS_PER_DAY; + ++days; + } + + result->tm_hour = rem / SECS_PER_HOUR; + rem %= SECS_PER_HOUR; + result->tm_min = rem / 60; + result->tm_sec = rem % 60; + + /* January 1, 1970 was a Thursday. */ + result->tm_wday = (4 + days) % 7; + if (result->tm_wday < 0) + result->tm_wday += 7; + + /* + * The following algorithm is, basically, Proposition 6.3 of Neri + * and Schneider [1]. In a few words: it works on the computational + * (fictitious) calendar where the year starts in March, month = 2 + * (*), and finishes in February, month = 13. This calendar is + * mathematically convenient because the day of the year does not + * depend on whether the year is leap or not. For instance: + * + * March 1st 0-th day of the year; + * ... + * April 1st 31-st day of the year; + * ... + * January 1st 306-th day of the year; (Important!) + * ... + * February 28th 364-th day of the year; + * February 29th 365-th day of the year (if it exists). + * + * After having worked out the date in the computational calendar + * (using just arithmetics) it's easy to convert it to the + * corresponding date in the Gregorian calendar. + * + * [1] "Euclidean Affine Functions and Applications to Calendar + * Algorithms". https://arxiv.org/abs/2102.06959 + * + * (*) The numbering of months follows tm more closely and thus, + * is slightly different from [1]. + */ + + udays = ((u64) days) + 2305843009213814918ULL; + + u64tmp = 4 * udays + 3; + century = div64_u64_rem(u64tmp, 146097, &u64tmp); + day_of_century = (u32) (u64tmp / 4); + + u32tmp = 4 * day_of_century + 3; + u64tmp = 2939745ULL * u32tmp; + year_of_century = upper_32_bits(u64tmp); + day_of_year = lower_32_bits(u64tmp) / 2939745 / 4; + + year = 100 * century + year_of_century; + is_leap_year = year_of_century ? !(year_of_century % 4) : !(century % 4); + + u32tmp = 2141 * day_of_year + 132377; + month = u32tmp >> 16; + day = ((u16) u32tmp) / 2141; + + /* + * Recall that January 1st is the 306-th day of the year in the + * computational (not Gregorian) calendar. + */ + is_Jan_or_Feb = day_of_year >= 306; + + /* Convert to the Gregorian calendar and adjust to Unix time. */ + year = year + is_Jan_or_Feb - 6313183731940000ULL; + month = is_Jan_or_Feb ? month - 12 : month; + day = day + 1; + day_of_year += is_Jan_or_Feb ? -306 : 31 + 28 + is_leap_year; + + /* Convert to tm's format. */ + result->tm_year = (long) (year - 1900); + result->tm_mon = (int) month; + result->tm_mday = (int) day; + result->tm_yday = (int) day_of_year; +} +EXPORT_SYMBOL(time64_to_tm); |