寻找素数分配线程算法

Posted 2021-07-15 qianbo_insist

最近需要求反向最大素数和正向最近素数，
1 计算机器的核心数目
2 拿到大于核心数目且最近的素数
3 拿到反向最大素数，两个算法

场景是，分配合适的线程，并且按照素数分配到合适的线程中去，比如根据URL如请求的是 /xn/live/234来计算hash值，并且将改链接session分配到一个线程中

计算有x个线程
链接为session，session1，session2 …，分配到x1，x2，x3…线程中

show me the code

#pragma once
#include <string.h>
#include <cmath>
#include <thread>
//注意prime是素数
static int rotating_hash(const char *key, int prime)
{
	int hash, i;
	int len = strlen(key);
	for (hash = len, i = 0; i < len; i++)
	{
		hash = (hash << 4 >> 28) ^ key[i];
		return (hash % prime);
	}
}

static int hash_add(const char* key, int prime)
{

	int hash, i;
	int len = strlen(key);
	for (hash = len, i = 0; i < len; i++)
		hash += key[i];
	return (hash % prime);
}

//求核数后面最大的素数
//只能被自己和1整除的数为素数

static int hash_next_prime(int num) {
	if (num == 1)
		return 2;
	if (num == 2)
		return 3;
	if (num % 2 == 0)
		++num;
	int i;
	bool flag = false;
	while (1)
	{
		flag = false;
		for (i = 3; i<num; i += 2)
			if (num % i == 0) {
				flag = true;
				break;
			}
		if (!flag)
			return num;
		num += 2;
	}
}
//寻找反向最大的素数
static int find_min_s(int a) {
	int m = 0;
	for (int i = a; i >0; i--) {
		m = 0;
		for (int j = 2; j <= std::sqrt(i); j++) {
			if (i%j == 0) {
				m = 1;
				break;
			}

		}
		if (m == 0) {
			//std::cout << i << " was the max prime";
			return i;
		}
	}
	if (m == 0) {
		//std::cout << a << " was the max prime";
		return a;
	}
}

测试

int main()
{
	const char * url = "xn/live/234";
	const char * url2 = "xn1/live/2345";
	const char * url3 = "xn2/live/234";
	const char * url4 = "xn/abc/23411";
	const char * url5 = "xn/abcd/234";
	const char * url6 = "xn/abcd/2345";
	const char * url7 = "xn/abcd/2346";
	const char * url8 = "xn/abcd/2347";
	const char * url9 = "xn/abcd/2348";
	const char * url10 = "xn/abcd/2349";
	const char * url11 = "xn2/abcd/2349";


	cout << hash_add(url, 7) << endl;
	cout << hash_add(url2, 7) << endl;
	cout << hash_add(url3, 7) << endl;
	cout << hash_add(url4, 7) << endl;
	cout << hash_add(url5, 7) << endl;
	cout << hash_add(url6, 7) << endl;
	cout << hash_add(url7, 7) << endl;
	cout << hash_add(url8, 7) << endl;
	cout << hash_add(url9, 7) << endl;
	cout << hash_add(url10, 7) << endl;
	cout << hash_add(url11, 7) << endl;

	int ct = core_thread();
	int g = hash_next_prime(ct);
	cout << "the prime is :" << g<<endl;
	cout << hash_add(url, g) << endl;

}

得到核数的函数

static int core_thread()
{
	static int g_thread_core = 0 ;
	if (g_thread_core > 0)
		return g_thread_core;
	int cpu_core = std::thread::hardware_concurrency();
	g_thread_core = hash_next_prime(cpu_core);
	return g_thread_core;
}