cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
Log | Files | Refs | README | LICENSE | sfeed.txt

timeconv.c (4629B)

      1// SPDX-License-Identifier: LGPL-2.0+
      2/*
      3 * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
      4 * This file is part of the GNU C Library.
      5 * Contributed by Paul Eggert (eggert@twinsun.com).
      6 *
      7 * The GNU C Library is free software; you can redistribute it and/or
      8 * modify it under the terms of the GNU Library General Public License as
      9 * published by the Free Software Foundation; either version 2 of the
     10 * License, or (at your option) any later version.
     11 *
     12 * The GNU C Library is distributed in the hope that it will be useful,
     13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
     14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     15 * Library General Public License for more details.
     16 *
     17 * You should have received a copy of the GNU Library General Public
     18 * License along with the GNU C Library; see the file COPYING.LIB.  If not,
     19 * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
     20 * Boston, MA 02111-1307, USA.
     21 */
     22
     23/*
     24 * Converts the calendar time to broken-down time representation
     25 *
     26 * 2009-7-14:
     27 *   Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com>
     28 * 2021-06-02:
     29 *   Reimplemented by Cassio Neri <cassio.neri@gmail.com>
     30 */
     31
     32#include <linux/time.h>
     33#include <linux/module.h>
     34#include <linux/kernel.h>
     35
     36#define SECS_PER_HOUR	(60 * 60)
     37#define SECS_PER_DAY	(SECS_PER_HOUR * 24)
     38
     39/**
     40 * time64_to_tm - converts the calendar time to local broken-down time
     41 *
     42 * @totalsecs:	the number of seconds elapsed since 00:00:00 on January 1, 1970,
     43 *		Coordinated Universal Time (UTC).
     44 * @offset:	offset seconds adding to totalsecs.
     45 * @result:	pointer to struct tm variable to receive broken-down time
     46 */
     47void time64_to_tm(time64_t totalsecs, int offset, struct tm *result)
     48{
     49	u32 u32tmp, day_of_century, year_of_century, day_of_year, month, day;
     50	u64 u64tmp, udays, century, year;
     51	bool is_Jan_or_Feb, is_leap_year;
     52	long days, rem;
     53	int remainder;
     54
     55	days = div_s64_rem(totalsecs, SECS_PER_DAY, &remainder);
     56	rem = remainder;
     57	rem += offset;
     58	while (rem < 0) {
     59		rem += SECS_PER_DAY;
     60		--days;
     61	}
     62	while (rem >= SECS_PER_DAY) {
     63		rem -= SECS_PER_DAY;
     64		++days;
     65	}
     66
     67	result->tm_hour = rem / SECS_PER_HOUR;
     68	rem %= SECS_PER_HOUR;
     69	result->tm_min = rem / 60;
     70	result->tm_sec = rem % 60;
     71
     72	/* January 1, 1970 was a Thursday. */
     73	result->tm_wday = (4 + days) % 7;
     74	if (result->tm_wday < 0)
     75		result->tm_wday += 7;
     76
     77	/*
     78	 * The following algorithm is, basically, Proposition 6.3 of Neri
     79	 * and Schneider [1]. In a few words: it works on the computational
     80	 * (fictitious) calendar where the year starts in March, month = 2
     81	 * (*), and finishes in February, month = 13. This calendar is
     82	 * mathematically convenient because the day of the year does not
     83	 * depend on whether the year is leap or not. For instance:
     84	 *
     85	 * March 1st		0-th day of the year;
     86	 * ...
     87	 * April 1st		31-st day of the year;
     88	 * ...
     89	 * January 1st		306-th day of the year; (Important!)
     90	 * ...
     91	 * February 28th	364-th day of the year;
     92	 * February 29th	365-th day of the year (if it exists).
     93	 *
     94	 * After having worked out the date in the computational calendar
     95	 * (using just arithmetics) it's easy to convert it to the
     96	 * corresponding date in the Gregorian calendar.
     97	 *
     98	 * [1] "Euclidean Affine Functions and Applications to Calendar
     99	 * Algorithms". https://arxiv.org/abs/2102.06959
    100	 *
    101	 * (*) The numbering of months follows tm more closely and thus,
    102	 * is slightly different from [1].
    103	 */
    104
    105	udays	= ((u64) days) + 2305843009213814918ULL;
    106
    107	u64tmp		= 4 * udays + 3;
    108	century		= div64_u64_rem(u64tmp, 146097, &u64tmp);
    109	day_of_century	= (u32) (u64tmp / 4);
    110
    111	u32tmp		= 4 * day_of_century + 3;
    112	u64tmp		= 2939745ULL * u32tmp;
    113	year_of_century	= upper_32_bits(u64tmp);
    114	day_of_year	= lower_32_bits(u64tmp) / 2939745 / 4;
    115
    116	year		= 100 * century + year_of_century;
    117	is_leap_year	= year_of_century ? !(year_of_century % 4) : !(century % 4);
    118
    119	u32tmp		= 2141 * day_of_year + 132377;
    120	month		= u32tmp >> 16;
    121	day		= ((u16) u32tmp) / 2141;
    122
    123	/*
    124	 * Recall that January 1st is the 306-th day of the year in the
    125	 * computational (not Gregorian) calendar.
    126	 */
    127	is_Jan_or_Feb	= day_of_year >= 306;
    128
    129	/* Convert to the Gregorian calendar and adjust to Unix time. */
    130	year		= year + is_Jan_or_Feb - 6313183731940000ULL;
    131	month		= is_Jan_or_Feb ? month - 12 : month;
    132	day		= day + 1;
    133	day_of_year	+= is_Jan_or_Feb ? -306 : 31 + 28 + is_leap_year;
    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}
    141EXPORT_SYMBOL(time64_to_tm);