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

struct primes {
    unsigned long int num;
    struct primes *next;
};    

void dump( struct primes *p, unsigned long int n, unsigned long int count );

void add_prime( unsigned long int number, struct primes *p );

int try_prime( unsigned long int num, struct primes *p);

#define runtime (finish - start)

FILE *DUMPME;

int main(int argc, char ** argv)
{
    int result;
    struct primes *p;
    unsigned long int number, n = 0, count = 0;
    time_t start, finish;
    if (argc == 0) { 
        printf ("Usage: %s [number]\n", argv[0]);
    }
    p = (struct primes *) malloc (sizeof(struct primes));
    p -> num = 0;
    time(&start);
    printf ("Prime Crunching"); 
    fflush(stdout);
    for (number = 1; number < 100000; number++) {
        result = try_prime(number, p);
        if (result) {
            fflush (stdout);
            count++;
            if (count == 1000) { 
                printf ("."); 
                count = 0;
                n++;
            }
            add_prime(number, p);
        }
    }
    time(&finish);
    DUMPME = fopen("prime.dump", "w");
    printf ("\nDumping primes...\n");
    dump(p, n, count);   
    printf ("Numbers per second: %i\n", (number + 1) / runtime);
    printf ("Elapsed time (actually crunching): %i seconds\n", runtime);
    return 0;
}

void add_prime ( unsigned long int number, struct primes *p ) {
    if ( p -> num == 0 ) {
        p -> num = number;
        p -> next = (struct primes *) malloc (sizeof(struct primes));
        p -> next -> num = 0;
    }
    else {
        add_prime( number, p -> next );
    }
}

void dump( struct primes *p, unsigned long int n, unsigned long int count )
{    
    for (; p -> num != 0; p = p -> next) {        
        fprintf (DUMPME, "%i\n", p -> num);
    }
    free(p);
    p = NULL;
    printf ("Primes found: %i\n", (n * 1000) + count);
    fclose (DUMPME);
}

int try_prime( unsigned long int n, struct primes *p )
{
    if (n == 1)
        return 1;
    if ( p -> num > (n / 2) ) { return 1; }         
    while (p -> num != 0) {
        if ( !(n % p -> num) && p -> num != 1 ) {
            return 0;
        }
        else {
            if (try_prime(n, p -> next)) {
                return 1;
            }        
            else {
                return 0;
            }
        }
    }
}