linux/kernel/time/timeconv.c

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time: Add SPDX license identifiers Update the time(r) core files files with the correct SPDX license identifier based on the license text in the file itself. The SPDX identifier is a legally binding shorthand, which can be used instead of the full boiler plate text. This work is based on a script and data from Philippe Ombredanne, Kate Stewart and myself. The data has been created with two independent license scanners and manual inspection. The following files do not contain any direct license information and have been omitted from the big initial SPDX changes: timeconst.bc: The .bc files were not touched time.c, timer.c, timekeeping.c: Licence was deduced from EXPORT_SYMBOL_GPL As those files do not contain direct license references they fall under the project license, i.e. GPL V2 only. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Kees Cook <keescook@chromium.org> Acked-by: Ingo Molnar <mingo@kernel.org> Acked-by: John Stultz <john.stultz@linaro.org> Acked-by: Corey Minyard <cminyard@mvista.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Kate Stewart <kstewart@linuxfoundation.org> Cc: Philippe Ombredanne <pombredanne@nexb.com> Cc: Russell King <rmk+kernel@armlinux.org.uk> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Nicolas Pitre <nicolas.pitre@linaro.org> Cc: David Riley <davidriley@chromium.org> Cc: Colin Cross <ccross@android.com> Cc: Mark Brown <broonie@kernel.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Link: https://lkml.kernel.org/r/20181031182252.879109557@linutronix.de
2018-10-31 18:21:09 +00:00
// 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);