I was just wondering why is that primes are used in a class’s hashCode() method? For example, when using Eclipse to generate my hashCode() method there is always the prime number 31 used: public int hashCode() { final int prime = 31; //… } References: Here is a good primer on Hashcode and article on … Read more
One thing that always strikes me as a non-cryptographer: Why is it so important to use prime numbers? What makes them so special in cryptography? Does anyone have a simple short explanation? (I am aware that there are many primers and that Applied Cryptography is the Bible, but as said: I am not looking to … Read more
Which is the fastest algorithm to find out prime numbers using C++? I have used sieve’s algorithm but I still want it to be faster! 18 Answers 18
This is the best algorithm I could come up. def get_primes(n): numbers = set(range(n, 1, -1)) primes = [] while numbers: p = numbers.pop() primes.append(p) numbers.difference_update(set(range(p*2, n+1, p))) return primes >>> timeit.Timer(stmt=”get_primes.get_primes(1000000)”, setup=’import get_primes’).timeit(1) 1.1499958793645562 Can it be made even faster? This code has a flaw: Since numbers is an unordered set, there is no … Read more
To test whether a number is prime or not, why do we have to test whether it is divisible only up to the square root of that number? 13 s 13 If a number n is not a prime, it can be factored into two factors a and b: n = a * b Now … Read more
