https://stackoverflow.com/questions/56853810/why-does-optimized-prime-factor-counting-algorithm-run-slower

PrimeFactors.java

package bench;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;

import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.ThreadLocalRandom;

@State(Scope.Benchmark)
public class PrimeFactors {

    // fast version
    static int countPrimeFactorsSet(int n) {
        Set<Integer> primeFactorSet = new HashSet<>();
        while (n % 2 == 0) {
            primeFactorSet.add(2);
            n /= 2;
        }
        for (int i = 3; i <= Math.sqrt(n); i += 2) {
            while (n % i == 0) {
                primeFactorSet.add(i);
                n /= i;
            }
        }
        if (n > 2) {
            primeFactorSet.add(n);
        }
        return primeFactorSet.size();
    }

    // slow version
    static int countPrimeFactorsCounter(int n) {
        int count = 0; // using simple int
        if (n % 2 == 0) {
            count ++; // only add on first division
            n /= 2;
            while (n % 2 == 0) {
                n /= 2;
            }
        }
        for (int i = 3; i <= Math.sqrt(n); i += 2) {
            if (n % i == 0) {
                count++; // only add on first division
                n /= i;
                while (n % i == 0) {
                    n /= i;
                }
            }
        }
        if (n > 2) {
            count++;
        }
        return count;
    }

    @Benchmark
    public int counter() {
        return countPrimeFactorsCounter(random());
    }

    @Benchmark
    public int set() {
        return countPrimeFactorsSet(random());
    }

    private int random() {
        return ThreadLocalRandom.current().nextInt(10_000_000) + 1;
    }
}

results.txt

Benchmark              Mode  Cnt     Score    Error   Units
PrimeFactors.counter  thrpt    5   717,976 ±  7,232  ops/ms
PrimeFactors.set      thrpt    5  1410,705 ± 15,894  ops/ms