Function sieve_generate_safe_primes 

pub fn sieve_generate_safe_primes(
    rng: &mut impl RngCore,
    bits: u32,
    amount: usize,
) -> Integer

Generate a random safe prime with a given sieve parameter.

For different bit sizes, different parameter value will give fastest generation, the higher bit size - the higher the sieve parameter. The best way to select the parameter is by trial. The one used by [generate_safe_prime] is indistinguishable from optimal for 500-1700 bit lengths.