OpenSSL::BN#bit_set?

static VALUE
ossl_bn_is_bit_set(VALUE self, VALUE bit)
{
    int b;
    BIGNUM *bn;

    b = NUM2INT(bit);
    GetBN(self, bn);
    if (BN_is_bit_set(bn, b)) {
        return Qtrue;
    }
    return Qfalse;
}