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
iso_date(char * p,int flag)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 }
81