util.c

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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 [email protected] (Volker Kuhlmann)
         * for pointing out the sign error.
         */
        if (-52 <= tz && tz <= 52)
            crtime -= tz * 15 * 60;
    }
    return crtime;
}