int asn1_generalizedtime_to_tm(struct tm *tm, const ASN1_GENERALIZEDTIME *d)
{
    static const int min[9] = { 0, 0, 1, 1, 0, 0, 0, 0, 0 };
    static const int max[9] = { 99, 99, 12, 31, 23, 59, 59, 12, 59 };
    char *a;
    int n, i, l, o;

    if (d->type != V_ASN1_GENERALIZEDTIME)
        return (0);
    l = d->length;
    a = (char *)d->data;
    o = 0;
    /*
     * GENERALIZEDTIME is similar to UTCTIME except the year is represented
     * as YYYY. This stuff treats everything as a two digit field so make
     * first two fields 00 to 99
     */
    if (l < 13)
        goto err;
    for (i = 0; i < 7; i++) {
        if ((i == 6) && ((a[o] == 'Z') || (a[o] == '+') || (a[o] == '-'))) {
            i++;
            if (tm)
                tm->tm_sec = 0;
            break;
        }
        if ((a[o] < '0') || (a[o] > '9'))
            goto err;
        n = a[o] - '0';
        if (++o > l)
            goto err;

        if ((a[o] < '0') || (a[o] > '9'))
            goto err;
        n = (n * 10) + a[o] - '0';
        if (++o > l)
            goto err;

        if ((n < min[i]) || (n > max[i]))
            goto err;
        if (tm) {
            switch (i) {
            case 0:
                tm->tm_year = n * 100 - 1900;
                break;
            case 1:
                tm->tm_year += n;
                break;
            case 2:
                tm->tm_mon = n - 1;
                break;
            case 3:
                tm->tm_mday = n;
                break;
            case 4:
                tm->tm_hour = n;
                break;
            case 5:
                tm->tm_min = n;
                break;
            case 6:
                tm->tm_sec = n;
                break;
            }
        }
    }
    /*
     * Optional fractional seconds: decimal point followed by one or more
     * digits.
     */
    if (a[o] == '.') {
        if (++o > l)
            goto err;
        i = o;
        while ((a[o] >= '0') && (a[o] <= '9') && (o <= l))
            o++;
        /* Must have at least one digit after decimal point */
        if (i == o)
            goto err;
    }

    if (a[o] == 'Z')
        o++;
    else if ((a[o] == '+') || (a[o] == '-')) {
        int offsign = a[o] == '-' ? 1 : -1, offset = 0;
        o++;
        if (o + 4 > l)
            goto err;
        for (i = 7; i < 9; i++) {
            if ((a[o] < '0') || (a[o] > '9'))
                goto err;
            n = a[o] - '0';
            o++;
            if ((a[o] < '0') || (a[o] > '9'))
                goto err;
            n = (n * 10) + a[o] - '0';
            if ((n < min[i]) || (n > max[i]))
                goto err;
            if (tm) {
                if (i == 7)
                    offset = n * 3600;
                else if (i == 8)
                    offset += n * 60;
            }
            o++;
        }
        if (offset && !OPENSSL_gmtime_adj(tm, 0, offset * offsign))
            return 0;
    } else if (a[o]) {
        /* Missing time zone information. */
        goto err;
    }
    return (o == l);
 err:
    return (0);
}