试图创建一个多线程程序来查找0-100000000之间的总素数

你好，我正在尝试使用POSIX线程库编写一个C++多线程程序，以查找1到10000000(1000万(之间的素数，并找出它需要多少微秒。。。

创建我的线程并运行它们完全正常，但我觉得在确定一个数字是否素数时，在我的素数函数中发现了一个错误。。。

我一直收到78496作为我的输出，然而我想要664579。下面是我的代码。任何提示或指示都将不胜感激。

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <unistd.h>
#include <iostream>
#include <sys/time.h> //measure the execution time of the computations
using namespace std;
//The number of thread to be generated
#define NUMBER_OF_THREADS 4
void * Prime(void* index);
long numbers[4] = {250000, 500000, 750000, 1000000};
long start_numbers[4] = {1, 250001, 500001, 750001};
int thread_numbers[4] = {0, 1, 2, 3};
int main(){
pthread_t tid[NUMBER_OF_THREADS];
int tn;
long sum = 0;
timeval start_time, end_time; 
double start_time_microseconds, end_time_microseconds;
gettimeofday(&start_time, NULL);
start_time_microseconds = start_time.tv_sec * 1000000 + start_time.tv_usec;
for(tn = 0; tn < NUMBER_OF_THREADS; tn++){
if (pthread_create(&tid[tn], NULL, Prime, (void *) &thread_numbers[tn]) == -1 ) {
perror("thread fail");
exit(-1);
}
}
long value[4];
for(int i = 0; i < NUMBER_OF_THREADS; i++){
if(pthread_join(tid[i],(void **) &value[i]) == 0){
sum = sum + value[i]; //add four sums together
}else{
perror("Thread join failed");
exit(-1);
}
}
//get the end time in microseconds
gettimeofday(&end_time, NULL);
end_time_microseconds = end_time.tv_sec * 1000000 + end_time.tv_usec;
//calculate the time passed
double time_passed = end_time_microseconds - start_time_microseconds;
cout << "Sum is: " << sum << endl;
cout << "Running time is: " << time_passed << " microseconds" << endl;
exit(0);
}

//Prime function
void* Prime(void* index){
int temp_index;
temp_index = *((int*)index);
long  sum_t = 0;
for(long i = start_numbers[temp_index]; i <= numbers[temp_index]; i++){
for (int j=2; j*j <= i; j++)
{
if (i % j == 0) 
{
break;
}
else if (j+1 > sqrt(i)) {
sum_t++;
}
}
}
cout << "Thread " << temp_index << " terminates" << endl;
pthread_exit( (void*) sum_t);
}```