gmt_offset

/*
 *  call-seq:
 *     time.gmt_offset => fixnum
 *     time.gmtoff     => fixnum
 *     time.utc_offset => fixnum
 *  
 *  Returns the offset in seconds between the timezone of <i>time</i>
 *  and UTC.
 *     
 *     t = Time.gm(2000,1,1,20,15,1)   #=> Sat Jan 01 20:15:01 UTC 2000
 *     t.gmt_offset                    #=> 0
 *     l = t.getlocal                  #=> Sat Jan 01 14:15:01 CST 2000
 *     l.gmt_offset                    #=> -21600
 */

static VALUE
time_utc_offset(time)
    VALUE time;
{
    struct time_object *tobj;

    GetTimeval(time, tobj);
    if (tobj->tm_got == 0) {
        time_get_tm(time, tobj->gmt);
    }

    if (tobj->gmt == 1) {
        return INT2FIX(0);
    }
    else {
#if defined(HAVE_STRUCT_TM_TM_GMTOFF)
        return INT2NUM(tobj->tm.tm_gmtoff);
#else
        struct tm *u, *l;
        time_t t;
        long off;
        l = &tobj->tm;
        t = tobj->tv.tv_sec;
        u = gmtime(&t);
        if (!u)
            rb_raise(rb_eArgError, "gmtime error");
        if (l->tm_year != u->tm_year)
            off = l->tm_year < u->tm_year ? -1 : 1;
        else if (l->tm_mon != u->tm_mon)
            off = l->tm_mon < u->tm_mon ? -1 : 1;
        else if (l->tm_mday != u->tm_mday)
            off = l->tm_mday < u->tm_mday ? -1 : 1;
        else
            off = 0;
        off = off * 24 + l->tm_hour - u->tm_hour;
        off = off * 60 + l->tm_min - u->tm_min;
        off = off * 60 + l->tm_sec - u->tm_sec;
        return LONG2FIX(off);
#endif
    }
}