// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/isofs/util.c
 */

#include <linux/time.h>
#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.
 */

struct timespec64 iso_date(u8 *p, int flags)
{
        int year, month, day, hour, minute, second, tz;
        struct timespec64 ts;

        if (flags & ISO_DATE_LONG_FORM) {
                year = (p[0] - '0') * 1000 +
                       (p[1] - '0') * 100 +
                       (p[2] - '0') * 10 +
                       (p[3] - '0') - 1900;
                month = ((p[4] - '0') * 10 + (p[5] - '0'));
                day = ((p[6] - '0') * 10 + (p[7] - '0'));
                hour = ((p[8] - '0') * 10 + (p[9] - '0'));
                minute = ((p[10] - '0') * 10 + (p[11] - '0'));
                second = ((p[12] - '0') * 10 + (p[13] - '0'));
                ts.tv_nsec = ((p[14] - '0') * 10 + (p[15] - '0')) * 10000000;
                tz = p[16];
        } else {
                year = p[0];
                month = p[1];
                day = p[2];
                hour = p[3];
                minute = p[4];
                second = p[5];
                ts.tv_nsec = 0;
                /* High sierra has no time zone */
                tz = flags & ISO_DATE_HIGH_SIERRA ? 0 : p[6];
        }

        if (year < 0) {
                ts.tv_sec = 0;
        } else {
                ts.tv_sec = mktime64(year+1900, month, day, hour, minute, 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)
                        ts.tv_sec -= tz * 15 * 60;
        }
        return ts;
}