Tech Space

Same specs as previous system, 8 hours to find all primes to ULONG_MAX.

#include <stdio.h>#include <malloc.h>#include <limits.h>#include <math.h>

struct linked_list{    unsigned long number;    struct linked_list *next;};

int main(int argc, char **argv){    unsigned long divisor, max_divisor, prime_test;    unsigned long max_prime_to_store;    struct linked_list *first=NULL, *current=NULL, *last=NULL;

    first=(struct linked_list *)malloc(sizeof(struct linked_list));    first->number = 2L;    first->next = NULL;    last = first;    printf("%lu\n", 2L);

    max_prime_to_store = 1L + sqrt(ULONG_MAX);

    for(prime_test = 3L; prime_test < ULONG_MAX; prime_test+=2L)    {        max_divisor=1L+sqrt(prime_test);        for(current = first; current && current->number <= max_divisor; current = current->next)        {            if(prime_test % current->number == 0)            {                break;            }        }        if(!current || current->number > max_divisor)        {            if(prime_test <= max_prime_to_store)            {                last->next = (struct linked_list *)malloc(sizeof(struct linked_list));                last = last->next;                last->next = NULL;                last->number = prime_test;            }            printf("%lu\n", prime_test);        }    }    return 0;}