954,498 Members — Technology Publication meets Social Media
Username:
Password:
Lost login information?
Have something to say? Contribute New Article Reply to this Article

Primality Test

I have a difficult function to write and I have no idea where to begin. Here is the definition of what I need to write:
"A function f(x,y) which returns true if the binary number formed by concatenating the bits of x, 8*y-1 zeroes and a one is prime, false otherwise. x is an array of bytes (unsigned char) and y is an unsigned integer comprised of two bytes (unsigned short)."
EG:
f(10,1234)=isPrime(00001010...0x9871...1)
I am just completely lost as to what to do. I think there should be a better way than actually creating a class that can store massive numbers and than doing the traditional primality check of:

bool isPrime(myLargeIntegerMimic a)
{
    for (myLargeIntegerMimic i=2; i*i<a; i++)
    {
        if (a%i==0)
            return false;
    }
    return true;
}


Since myLargeIntegerMimic would have to store a massive array of 'y' bytes and then would have to successfully do multiplication and modulation on it, this would be extremely slow. I am hoping that I am missing some kind of short-cut.

Labdabeta
Posting Pro in Training
489 posts since Feb 2011
Reputation Points: 27
Solved Threads: 18
 

This article has been dead for over three months

Post: Markdown Syntax: Formatting Help
You
View similar articles that have also been tagged: