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       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                 :            :  * Based on code from glibc-2.6
      26                 :            :  *
      27                 :            :  * 2009-7-14:
      28                 :            :  *   Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com>
      29                 :            :  */
      30                 :            : 
      31                 :            : #include <linux/time.h>
      32                 :            : #include <linux/module.h>
      33                 :            : 
      34                 :            : /*
      35                 :            :  * Nonzero if YEAR is a leap year (every 4 years,
      36                 :            :  * except every 100th isn't, and every 400th is).
      37                 :            :  */
      38                 :            : static int __isleap(long year)
      39                 :            : {
      40                 :          3 :         return (year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0);
      41                 :            : }
      42                 :            : 
      43                 :            : /* do a mathdiv for long type */
      44                 :            : static long math_div(long a, long b)
      45                 :            : {
      46                 :          2 :         return a / b - (a % b < 0);
      47                 :            : }
      48                 :            : 
      49                 :            : /* How many leap years between y1 and y2, y1 must less or equal to y2 */
      50                 :          2 : static long leaps_between(long y1, long y2)
      51                 :            : {
      52                 :          2 :         long leaps1 = math_div(y1 - 1, 4) - math_div(y1 - 1, 100)
      53                 :            :                 + math_div(y1 - 1, 400);
      54                 :          2 :         long leaps2 = math_div(y2 - 1, 4) - math_div(y2 - 1, 100)
      55                 :            :                 + math_div(y2 - 1, 400);
      56                 :          2 :         return leaps2 - leaps1;
      57                 :            : }
      58                 :            : 
      59                 :            : /* How many days come before each month (0-12). */
      60                 :            : static const unsigned short __mon_yday[2][13] = {
      61                 :            :         /* Normal years. */
      62                 :            :         {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
      63                 :            :         /* Leap years. */
      64                 :            :         {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366}
      65                 :            : };
      66                 :            : 
      67                 :            : #define SECS_PER_HOUR   (60 * 60)
      68                 :            : #define SECS_PER_DAY    (SECS_PER_HOUR * 24)
      69                 :            : 
      70                 :            : /**
      71                 :            :  * time64_to_tm - converts the calendar time to local broken-down time
      72                 :            :  *
      73                 :            :  * @totalsecs   the number of seconds elapsed since 00:00:00 on January 1, 1970,
      74                 :            :  *              Coordinated Universal Time (UTC).
      75                 :            :  * @offset      offset seconds adding to totalsecs.
      76                 :            :  * @result      pointer to struct tm variable to receive broken-down time
      77                 :            :  */
      78                 :          3 : void time64_to_tm(time64_t totalsecs, int offset, struct tm *result)
      79                 :            : {
      80                 :            :         long days, rem, y;
      81                 :            :         int remainder;
      82                 :            :         const unsigned short *ip;
      83                 :            : 
      84                 :          3 :         days = div_s64_rem(totalsecs, SECS_PER_DAY, &remainder);
      85                 :          3 :         rem = remainder;
      86                 :          3 :         rem += offset;
      87                 :          3 :         while (rem < 0) {
      88                 :          0 :                 rem += SECS_PER_DAY;
      89                 :          0 :                 --days;
      90                 :            :         }
      91                 :          3 :         while (rem >= SECS_PER_DAY) {
      92                 :          0 :                 rem -= SECS_PER_DAY;
      93                 :          0 :                 ++days;
      94                 :            :         }
      95                 :            : 
      96                 :          3 :         result->tm_hour = rem / SECS_PER_HOUR;
      97                 :          3 :         rem %= SECS_PER_HOUR;
      98                 :          3 :         result->tm_min = rem / 60;
      99                 :          3 :         result->tm_sec = rem % 60;
     100                 :            : 
     101                 :            :         /* January 1, 1970 was a Thursday. */
     102                 :          3 :         result->tm_wday = (4 + days) % 7;
     103                 :          3 :         if (result->tm_wday < 0)
     104                 :          0 :                 result->tm_wday += 7;
     105                 :            : 
     106                 :            :         y = 1970;
     107                 :            : 
     108                 :          3 :         while (days < 0 || days >= (__isleap(y) ? 366 : 365)) {
     109                 :            :                 /* Guess a corrected year, assuming 365 days per year. */
     110                 :          2 :                 long yg = y + math_div(days, 365);
     111                 :            : 
     112                 :            :                 /* Adjust DAYS and Y to match the guessed year. */
     113                 :          2 :                 days -= (yg - y) * 365 + leaps_between(y, yg);
     114                 :            :                 y = yg;
     115                 :            :         }
     116                 :            : 
     117                 :          3 :         result->tm_year = y - 1900;
     118                 :            : 
     119                 :          3 :         result->tm_yday = days;
     120                 :            : 
     121                 :          3 :         ip = __mon_yday[__isleap(y)];
     122                 :          3 :         for (y = 11; days < ip[y]; y--)
     123                 :          3 :                 continue;
     124                 :          3 :         days -= ip[y];
     125                 :            : 
     126                 :          3 :         result->tm_mon = y;
     127                 :          3 :         result->tm_mday = days + 1;
     128                 :          3 : }
     129                 :            : EXPORT_SYMBOL(time64_to_tm);