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       1                 :            : // SPDX-License-Identifier: GPL-2.0
       2                 :            : /*
       3                 :            :  *  linux/fs/isofs/util.c
       4                 :            :  */
       5                 :            : 
       6                 :            : #include <linux/time.h>
       7                 :            : #include "isofs.h"
       8                 :            : 
       9                 :            : /* 
      10                 :            :  * We have to convert from a MM/DD/YY format to the Unix ctime format.
      11                 :            :  * We have to take into account leap years and all of that good stuff.
      12                 :            :  * Unfortunately, the kernel does not have the information on hand to
      13                 :            :  * take into account daylight savings time, but it shouldn't matter.
      14                 :            :  * The time stored should be localtime (with or without DST in effect),
      15                 :            :  * and the timezone offset should hold the offset required to get back
      16                 :            :  * to GMT.  Thus  we should always be correct.
      17                 :            :  */
      18                 :            : 
      19                 :          0 : int iso_date(u8 *p, int flag)
      20                 :            : {
      21                 :          0 :         int year, month, day, hour, minute, second, tz;
      22                 :          0 :         int crtime;
      23                 :            : 
      24                 :          0 :         year = p[0];
      25                 :          0 :         month = p[1];
      26                 :          0 :         day = p[2];
      27                 :          0 :         hour = p[3];
      28                 :          0 :         minute = p[4];
      29                 :          0 :         second = p[5];
      30         [ #  # ]:          0 :         if (flag == 0) tz = p[6]; /* High sierra has no time zone */
      31                 :            :         else tz = 0;
      32                 :            :         
      33                 :          0 :         if (year < 0) {
      34                 :            :                 crtime = 0;
      35                 :            :         } else {
      36                 :          0 :                 crtime = mktime64(year+1900, month, day, hour, minute, second);
      37                 :            : 
      38                 :            :                 /* sign extend */
      39         [ #  # ]:          0 :                 if (tz & 0x80)
      40                 :          0 :                         tz |= (-1 << 8);
      41                 :            :                 
      42                 :            :                 /* 
      43                 :            :                  * The timezone offset is unreliable on some disks,
      44                 :            :                  * so we make a sanity check.  In no case is it ever
      45                 :            :                  * more than 13 hours from GMT, which is 52*15min.
      46                 :            :                  * The time is always stored in localtime with the
      47                 :            :                  * timezone offset being what get added to GMT to
      48                 :            :                  * get to localtime.  Thus we need to subtract the offset
      49                 :            :                  * to get to true GMT, which is what we store the time
      50                 :            :                  * as internally.  On the local system, the user may set
      51                 :            :                  * their timezone any way they wish, of course, so GMT
      52                 :            :                  * gets converted back to localtime on the receiving
      53                 :            :                  * system.
      54                 :            :                  *
      55                 :            :                  * NOTE: mkisofs in versions prior to mkisofs-1.10 had
      56                 :            :                  * the sign wrong on the timezone offset.  This has now
      57                 :            :                  * been corrected there too, but if you are getting screwy
      58                 :            :                  * results this may be the explanation.  If enough people
      59                 :            :                  * complain, a user configuration option could be added
      60                 :            :                  * to add the timezone offset in with the wrong sign
      61                 :            :                  * for 'compatibility' with older discs, but I cannot see how
      62                 :            :                  * it will matter that much.
      63                 :            :                  *
      64                 :            :                  * Thanks to kuhlmav@elec.canterbury.ac.nz (Volker Kuhlmann)
      65                 :            :                  * for pointing out the sign error.
      66                 :            :                  */
      67         [ #  # ]:          0 :                 if (-52 <= tz && tz <= 52)
      68                 :          0 :                         crtime -= tz * 15 * 60;
      69                 :            :         }
      70                 :          0 :         return crtime;
      71                 :            : }