original development tree for Linux kernel GTP module; now long in mainline.
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/*
* linux/fs/isofs/util.c
*/
#include "isofs.h"
/*
* We have to convert from a MM/DD/YY format to the Unix ctime format.
* We have to take into account leap years and all of that good stuff.
* Unfortunately, the kernel does not have the information on hand to
* take into account daylight savings time, but it shouldn't matter.
* The time stored should be localtime (with or without DST in effect),
* and the timezone offset should hold the offset required to get back
* to GMT. Thus we should always be correct.
*/
int iso_date(char * p, int flag)
{
int year, month, day, hour, minute, second, tz;
int crtime, days, i;
year = p[0] - 70;
month = p[1];
day = p[2];
hour = p[3];
minute = p[4];
second = p[5];
if (flag == 0) tz = p[6]; /* High sierra has no time zone */
else tz = 0;
if (year < 0) {
crtime = 0;
} else {
int monlen[12] = {31,28,31,30,31,30,31,31,30,31,30,31};
days = year * 365;
if (year > 2)
days += (year+1) / 4;
for (i = 1; i < month; i++)
days += monlen[i-1];
if (((year+2) % 4) == 0 && month > 2)
days++;
days += day - 1;
crtime = ((((days * 24) + hour) * 60 + minute) * 60)
+ second;
/* sign extend */
if (tz & 0x80)
tz |= (-1 << 8);
/*
* The timezone offset is unreliable on some disks,
* so we make a sanity check. In no case is it ever
* more than 13 hours from GMT, which is 52*15min.
* The time is always stored in localtime with the
* timezone offset being what get added to GMT to
* get to localtime. Thus we need to subtract the offset
* to get to true GMT, which is what we store the time
* as internally. On the local system, the user may set
* their timezone any way they wish, of course, so GMT
* gets converted back to localtime on the receiving
* system.
*
* NOTE: mkisofs in versions prior to mkisofs-1.10 had
* the sign wrong on the timezone offset. This has now
* been corrected there too, but if you are getting screwy
* results this may be the explanation. If enough people
* complain, a user configuration option could be added
* to add the timezone offset in with the wrong sign
* for 'compatibility' with older discs, but I cannot see how
* it will matter that much.
*
* Thanks to kuhlmav@elec.canterbury.ac.nz (Volker Kuhlmann)
* for pointing out the sign error.
*/
if (-52 <= tz && tz <= 52)
crtime -= tz * 15 * 60;
}
return crtime;
}