My multithreaded implementation in C of finding primes, 10x faster than PyPy implementation .

findingPrimesMulti.c

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <time.h>
#include <pthread.h>
#include <math.h>

struct thread_args{
    int start_number;
    int end_number;
};

void* calculate_thread(void *p) 
{   
    struct thread_args *args = (struct thread_args *) p;
    int start_number = args->start_number;
    int end_number = args->end_number;
    int noPrimes = 0;

    for (unsigned int i = start_number; i <= end_number; i++){
        bool found = true;

        for (unsigned int div = 2; div < i; div++){
            if((i % div) == 0){
                found = false;
                break;
            }
        }

        if(found == true){
            noPrimes++;
        }
        
    }

    free (args);
    pthread_exit((void*)(intptr_t) noPrimes);
} 


int main() {

    int END_NUMBER = 200000;
    int THREAD_COUNT = 6;



    int noPrimes = 0;
    time_t start, end;
    double diff;
    time (&start);

    printf("Finding all primes up to: %d\n", END_NUMBER);
    
    int total = 0;

    pthread_t tid[THREAD_COUNT];

    int chunk_size = floor(END_NUMBER/THREAD_COUNT);
    for (int thread_id = 0; thread_id < THREAD_COUNT; thread_id++){
        struct thread_args *args = malloc (sizeof (struct thread_args));
        args->start_number = chunk_size*thread_id;
        args->end_number = chunk_size*(thread_id+1);
        pthread_create (&tid[thread_id], NULL, calculate_thread, (void*) args);
        printf("Created thread %i \n", thread_id);
        //printf("%d to %d\n", args->start_number, args->end_number);
    }

    for (int thread_id = 0; thread_id < THREAD_COUNT; thread_id++){
        void *sum = NULL;
        pthread_join (tid[thread_id], &sum);
        total += (int)(intptr_t) sum;
    }

    time (&end);
    diff = difftime (end,start);
    printf("Took: %.2lfs, found: %i", diff, total);
    
    return 0;
}