prime?

static VALUE
ossl_bn_is_prime(int argc, VALUE *argv, VALUE self)
{
    BIGNUM *bn;
    VALUE vchecks;
    int checks = BN_prime_checks;

    if (rb_scan_args(argc, argv, "01", &vchecks) == 1) {
        checks = NUM2INT(vchecks);
    }
    GetBN(self, bn);
    switch (BN_is_prime(bn, checks, NULL, ossl_bn_ctx, NULL)) {
    case 1:
        return Qtrue;
    case 0:
        return Qfalse;
    default:
        ossl_raise(eBNError, NULL);
    }
    /* not reachable */
    return Qnil;
}