LXR linux/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
  17int 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}               
  81