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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142// 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);