int tls1_ec_nid2curve_id(int nid)
{
    /* ECC curves from RFC 4492 and RFC 7027 */
    switch (nid) {
    case NID_sect163k1:        /* sect163k1 (1) */
        return 1;
    case NID_sect163r1:        /* sect163r1 (2) */
        return 2;
    case NID_sect163r2:        /* sect163r2 (3) */
        return 3;
    case NID_sect193r1:        /* sect193r1 (4) */
        return 4;
    case NID_sect193r2:        /* sect193r2 (5) */
        return 5;
    case NID_sect233k1:        /* sect233k1 (6) */
        return 6;
    case NID_sect233r1:        /* sect233r1 (7) */
        return 7;
    case NID_sect239k1:        /* sect239k1 (8) */
        return 8;
    case NID_sect283k1:        /* sect283k1 (9) */
        return 9;
    case NID_sect283r1:        /* sect283r1 (10) */
        return 10;
    case NID_sect409k1:        /* sect409k1 (11) */
        return 11;
    case NID_sect409r1:        /* sect409r1 (12) */
        return 12;
    case NID_sect571k1:        /* sect571k1 (13) */
        return 13;
    case NID_sect571r1:        /* sect571r1 (14) */
        return 14;
    case NID_secp160k1:        /* secp160k1 (15) */
        return 15;
    case NID_secp160r1:        /* secp160r1 (16) */
        return 16;
    case NID_secp160r2:        /* secp160r2 (17) */
        return 17;
    case NID_secp192k1:        /* secp192k1 (18) */
        return 18;
    case NID_X9_62_prime192v1: /* secp192r1 (19) */
        return 19;
    case NID_secp224k1:        /* secp224k1 (20) */
        return 20;
    case NID_secp224r1:        /* secp224r1 (21) */
        return 21;
    case NID_secp256k1:        /* secp256k1 (22) */
        return 22;
    case NID_X9_62_prime256v1: /* secp256r1 (23) */
        return 23;
    case NID_secp384r1:        /* secp384r1 (24) */
        return 24;
    case NID_secp521r1:        /* secp521r1 (25) */
        return 25;
    case NID_brainpoolP256r1:  /* brainpoolP256r1 (26) */
        return 26;
    case NID_brainpoolP384r1:  /* brainpoolP384r1 (27) */
        return 27;
    case NID_brainpoolP512r1:  /* brainpool512r1 (28) */
        return 28;
    default:
        return 0;
    }
}

Unknown