#include <time.h>
#include <stdio.h>

#define ID_TIME_T time_t

int DST_MODE = 0xDEADBEEF;

long Sys_DosToUnixTime( unsigned long dostime ) {
    ID_TIME_T unix_time = 0;
    unsigned int sec, min, hour, day, mon, year;
    struct tm dostm;

    // break dos time down into its sec, min, hour components
    sec = (dostime & 0x1F) * 2;
    min = (dostime & 0x7E0) >> 5;
    hour = (dostime & 0xF800)  >> 11;

    // temporarily remove time component
    year = dostime >> 16;

    // break dos date down into its day, month, year components
    day = year & 0x1F;
    mon = (year & 0x1E0) >> 5;
    year = (year >> 9) + 1980;

    printf("Y%u M%u D%u  h%u m%u s%u\n", year, mon, day, hour, min, sec);
    if (sec <= 60 && min <= 59 && hour <= 23 && day >= 1 && day <= 31 && mon >= 1 && mon <= 12 && year <= 2107) {
        dostm.tm_sec = sec;
        dostm.tm_min = min;
        dostm.tm_hour = hour;
        dostm.tm_mday = day;
        dostm.tm_mon = mon - 1;
        dostm.tm_year = year - 1900;

        if (DST_MODE != 0xDEADBEEF)
            dostm.tm_isdst = DST_MODE;

        printf("Y%u M%u D%u  h%u m%u s%u\n", dostm.tm_year, dostm.tm_mon, dostm.tm_mday, dostm.tm_hour, dostm.tm_min, dostm.tm_sec);
        unix_time = mktime(&dostm);
    }

    return (long) unix_time;
}

int main() {
    printf("%ld\n", Sys_DosToUnixTime(0x4499A9C0));
    DST_MODE = -1;
    printf("%ld\n", Sys_DosToUnixTime(0x4499A9C0));
    DST_MODE = 0;
    printf("%ld\n", Sys_DosToUnixTime(0x4499A9C0));
    DST_MODE = 1;
    printf("%ld\n", Sys_DosToUnixTime(0x4499A9C0));
    return 0;
}