fs/isofs/util.c

   1 /*
   2  *  linux/fs/isofs/util.c
   3  */
   4
   5 #include "isofs.h"
   6
   7 /*
   8  * We have to convert from a MM/DD/YY format to the Unix ctime format.
   9  * We have to take into account leap years and all of that good stuff.
  10  * Unfortunately, the kernel does not have the information on hand to
  11  * take into account daylight savings time, but it shouldn't matter.
  12  * The time stored should be localtime (with or without DST in effect),
  13  * and the timezone offset should hold the offset required to get back
  14  * to GMT.  Thus  we should always be correct.
  15  */
  16
  17 int iso_date(char * p, int flag)
  18 {
  19         int year, month, day, hour, minute, second, tz;
  20         int crtime, days, i;
  21
  22         year = p[0] - 70;
  23         month = p[1];
  24         day = p[2];
  25         hour = p[3];
  26         minute = p[4];
  27         second = p[5];
  28         if (flag == 0) tz = p[6]; /* High sierra has no time zone */
  29         else tz = 0;
  30
  31         if (year < 0) {
  32                 crtime = 0;
  33         } else {
  34                 int monlen[12] = {31,28,31,30,31,30,31,31,30,31,30,31};
  35
  36                 days = year * 365;
  37                 if (year > 2)
  38                         days += (year+1) / 4;
  39                 for (i = 1; i < month; i++)
  40                         days += monlen[i-1];
  41                 if (((year+2) % 4) == 0 && month > 2)
  42                         days++;
  43                 days += day - 1;
  44                 crtime = ((((days * 24) + hour) * 60 + minute) * 60)
  45                         + second;
  46
  47                 /* sign extend */
  48                 if (tz & 0x80)
  49                         tz |= (-1 << 8);
  50
  51                 /*
  52                  * The timezone offset is unreliable on some disks,
  53                  * so we make a sanity check.  In no case is it ever
  54                  * more than 13 hours from GMT, which is 52*15min.
  55                  * The time is always stored in localtime with the
  56                  * timezone offset being what get added to GMT to
  57                  * get to localtime.  Thus we need to subtract the offset
  58                  * to get to true GMT, which is what we store the time
  59                  * as internally.  On the local system, the user may set
  60                  * their timezone any way they wish, of course, so GMT
  61                  * gets converted back to localtime on the receiving
  62                  * system.
  63                  *
  64                  * NOTE: mkisofs in versions prior to mkisofs-1.10 had
  65                  * the sign wrong on the timezone offset.  This has now
  66                  * been corrected there too, but if you are getting screwy
  67                  * results this may be the explanation.  If enough people
  68                  * complain, a user configuration option could be added
  69                  * to add the timezone offset in with the wrong sign
  70                  * for 'compatibility' with older discs, but I cannot see how
  71                  * it will matter that much.
  72                  *
  73                  * Thanks to kuhlmav@elec.canterbury.ac.nz (Volker Kuhlmann)
  74                  * for pointing out the sign error.
  75                  */
  76                 if (-52 <= tz && tz <= 52)
  77                         crtime -= tz * 15 * 60;
  78         }
  79         return crtime;
  80 }