int X509_cmp(const X509 *a, const X509 *b)
{
    int rv;
    /* ensure hash is valid */
    X509_check_purpose((X509 *)a, -1, 0);
    X509_check_purpose((X509 *)b, -1, 0);

    rv = memcmp(a->sha1_hash, b->sha1_hash, SHA_DIGEST_LENGTH);
    if (rv)
        return rv;
    /* Check for match against stored encoding too */
    if (!a->cert_info.enc.modified && !b->cert_info.enc.modified) {
        if (a->cert_info.enc.len < b->cert_info.enc.len)
            return -1;
        if (a->cert_info.enc.len > b->cert_info.enc.len)
            return 1;
        return memcmp(a->cert_info.enc.enc, b->cert_info.enc.enc,
                      a->cert_info.enc.len);
    }
    return rv;
}