Large Prime Number Generator

   I was using a combination of code from my previous posts etc and while looking at the code, I realized something, why do I need to repeat so much of it? I thought I could possibly optimize this a bit (Method still slow as crap). The first thing I did was make it so that each new random number generated will all have the same length in bits. Because they are all the same length in bits I don't have to generate new random numbers each time for the potential witnesses. Another thing was I can just set the length of bits instead of using the not so accurate tobytearray.length or using my own function to get bit length, I can just set it. I also added a multiple of 5 check before the iterations so that it doesn't try checking a number that ends in 5 (because primes larger than 2 only end in 1,3,7,9) instead it makes the number end in 3 by subtracting 2. For ease iterations can be set manually, if not the number of iterations is the square root of the length.

Code Note: Line 27 can be changed to:
"PrimeGen -= X" *X can be any even number
Depends on what you want the function to do when the current number isn't a prime.

Note: As always any errors or improvements please post in comments.