测试了三种优化级别的素数判断方案。

cpp
#include <iostream>
#include <algorithm>
#include <cmath>
#include <catch2/catch.hpp>

bool is_prime_0(int n) {
    for(int i = 2; i < n; ++i) {
        if (n % i == 0)
            return false;
    }
    return true;
}

bool is_prime_1(int n) {
    if (n % 2 == 0)
        return n == 2;
    int sq = floor(sqrt(n));
    for (int i = sq | 1; i > 1; i -= 2) {
        if (n % i == 0) {
            return false;
        }
    }
    return true;
}

bool is_prime_2(int n) {
    if (n == 2 || n == 3)
        return true;
    if (n % 6 != 1 || n % 6 != 5)
        return false;
    int sq = floor(sqrt(n));
    for(int i = 5;i <= sq; i += 6) {       
        if(n % i == 0 || n % (i+2) == 0)  
            return false;
    }
    return true;
}

TEST_CASE("Is Prime") {
    int num = 9989899;

    BENCHMARK("is_prime_0") {
        return is_prime_0(num);
    };

    BENCHMARK("is_prime_1") {
        return is_prime_1(num);
    };

    BENCHMARK("is_prime_2") {
        return is_prime_2(num);
    };
}

Benchmark 结果

benchmark name                       samples       iterations    estimated
                                     mean          low mean      high mean
                                     std dev       low std dev   high std dev
-------------------------------------------------------------------------------
is_prime_0                                     100             1     3.11125 s 
                                        32.4578 ms    31.9605 ms    33.1967 ms 
                                        3.04949 ms      2.275 ms    4.22213 ms 
                                                                               
is_prime_1                                     100             7      3.374 ms 
                                        4.72644 us    4.63879 us    5.03562 us 
                                        735.203 ns    234.881 ns    1.64281 us 
                                                                               
is_prime_2                                     100         31531     3.1531 ms 
                                        1.27671 ns    1.15347 ns    1.70551 ns 
                                        1.04434 ns   0.334288 ns    2.36015 ns