It's not a primality test. A primality test determines whether or not a single given integer is prime. The circuit I described checks that the product of two

It's not a primality test. A primality test determines whether or not a single given integer is prime. The circuit I described checks that the product of two arbitrary input integers is a specific known integer. By solving the decision problem for each bit independently you can determine all bits of the 2 input integers and hence factor the known target.