I am no JAVA coder so I stick with C++. Also this is not an direct answer to your question (sorry for that but I can not debug JAVA) take this as some pointers which way to go or check… Sieves of Eratosthenes Parallelization is possible but not with big enough speed gain. Instead I … Read more
You can do this faster using a nearly optimal trial division sieve in one (long) line like this: Enumerable.Range(0, Math.Floor(2.52*Math.Sqrt(num)/Math.Log(num))).Aggregate( Enumerable.Range(2, num-1).ToList(), (result, index) => { var bp = result[index]; var sqr = bp * bp; result.RemoveAll(i => i >= sqr && i % bp == 0); return result; } ); The approximation formula for … Read more
The basic idea of a segmented sieve is to choose the sieving primes less than the square root of n, choose a reasonably large segment size that nevertheless fits in memory, and then sieve each of the segments in turn, starting with the smallest. At the first segment, the smallest multiple of each sieving prime … Read more
You’re not quite implementing the correct algorithm: In your first example, primes_sieve doesn’t maintain a list of primality flags to strike/unset (as in the algorithm), but instead resizes a list of integers continuously, which is very expensive: removing an item from a list requires shifting all subsequent items down by one. In the second example, … Read more