// 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);