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