erdes001.c

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

#include <primesieve.h>

/*
    SIZE%(NTHREADS*2) must be == 0
*/

#define FILENAME "/dev/stdout"
#define SIZE 100000000 // number of fractions to compute
#define NTHREADS 4 // number of threads to utilize
/*digests per thread. please, choose reasonable number,
not smth like 123. checks are not performed to guarantee accuracy*/
#define RESOLUTION 10

long double sum;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_barrier_t barrier;

unsigned long int primes[NTHREADS] = { 0 };

void *job (void *arg)
{
    unsigned long int index, n, p, size, end;
    long double localsum;
    primesieve_iterator it;
    time_t t;
    struct tm *time_p;
    FILE *f;
    char buf[BUFSIZ];

    pthread_mutex_lock(&mutex);

    index = *((unsigned long int*)arg);
    size = SIZE/NTHREADS;
    n = size*index;

    if (index == NTHREADS - 1)
    {
        end = SIZE - 1;
    }
    else
    {
        end = n + size - 1;
    }

    f = fopen(FILENAME, "w");
    setvbuf(f, buf, _IOLBF, BUFSIZ);

    fprintf(f, "%ld: from %ld to %ld\n", index, n + 1, end + 1);

    time(&t);
    time_p = localtime(&t);
    fprintf(f, "[%04d-%02d-%02d %02d:%02d:%02d] %ld: skipping...\n",
        time_p->tm_year + 1900, time_p->tm_mon + 1, time_p->tm_mday,
        time_p->tm_hour, time_p->tm_min, time_p->tm_sec, index);

    if (primes[index])
    {
        primesieve_init(&it);
        p = primes[index];
        primesieve_skipto(&it, p - 1, p + size);
    }
    else
    {
        primesieve_init(&it);
        p = primesieve_nth_prime(n + 1, 0);
        printf("%ld\n", p);
        primesieve_skipto(&it, p - 1, p + size);
    }

    pthread_mutex_unlock(&mutex);

    pthread_barrier_wait(&barrier);

    time(&t);
    time_p = localtime(&t);
    fprintf(f, "[%04d-%02d-%02d %02d:%02d:%02d] %ld: calculating...\n",
        time_p->tm_year + 1900, time_p->tm_mon + 1, time_p->tm_mday,
        time_p->tm_hour, time_p->tm_min, time_p->tm_sec, index);

    while (n <= end)
    {
        localsum -= (++n)/(long double)primesieve_next_prime(&it);

        time(&t);
        time_p = localtime(&t);
        fprintf(f, "[%04d-%02d-%02d %02d:%02d:%02d] %ld: %ld\n",
            time_p->tm_year + 1900, time_p->tm_mon + 1, time_p->tm_mday,
            time_p->tm_hour, time_p->tm_min, time_p->tm_sec, index, n);

        localsum += (++n)/(long double)primesieve_next_prime(&it);

        time(&t);
        time_p = localtime(&t);
        fprintf(f, "[%04d-%02d-%02d %02d:%02d:%02d] %ld: %ld\n",
            time_p->tm_year + 1900, time_p->tm_mon + 1, time_p->tm_mday,
            time_p->tm_hour, time_p->tm_min, time_p->tm_sec, index, n);

        for (unsigned long int i = 0; i < size/RESOLUTION - 1; i++)
        {
            localsum -= (++n)/(long double)primesieve_next_prime(&it);
            localsum += (++n)/(long double)primesieve_next_prime(&it);
        }
    }

    primesieve_free_iterator(&it);

    time(&t);
    time_p = localtime(&t);
    fprintf(f, "[%04d-%02d-%02d %02d:%02d:%02d] %ld: calculated! partial result: %.20Lf\n",
        time_p->tm_year + 1900, time_p->tm_mon + 1, time_p->tm_mday,
        time_p->tm_hour, time_p->tm_min, time_p->tm_sec, index, localsum);

    fclose(f);

    sum += localsum;

    return NULL;
}

int main (int argc, char *argv[])
{
    pthread_t threads[NTHREADS];
    unsigned long int args[NTHREADS];
    int i;
    FILE *f;
    char buf[BUFSIZ];
    time_t t;
    struct tm *time_p;

    sum = 0.0L;

    pthread_barrier_init(&barrier, NULL, NTHREADS);

    f = fopen(FILENAME, "w");
    setvbuf(f, buf, _IOLBF, BUFSIZ);

    time(&t);
    time_p = localtime(&t);

    fprintf(f, "[%04d-%02d-%02d %02d:%02d:%02d] M: started\n\n",
        time_p->tm_year + 1900, time_p->tm_mon + 1, time_p->tm_mday,
        time_p->tm_hour, time_p->tm_min, time_p->tm_sec);

    for (i = 0; i < argc - 1; i++)
    {
        primes[i] = strtoul(argv[i + 1], NULL, 10);
        printf("%ld\n", primes[i]);
    }

    for (i = 0; i < NTHREADS; i++)
    {
        args[i] = i;
        pthread_create(&threads[i], NULL, job, &args[i]);
    }

    for (i = 0; i < NTHREADS; i++)
    {
        pthread_join(threads[i], NULL);
    }

    fprintf(f, "\nM: total result: %.20Lf\n", sum);

    fclose(f);

    return EXIT_SUCCESS;
}