• 출처 : http://www.www.hantor.net/xe/?document_srl=75842

/*
 ============================================================================
 Name        : calc_primenum.c
 Author      :
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */
 
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
 
int main()
{
        int *prime_list = NULL;
        int size = 0;
 
        int n = 0;
        int i, j;
 
        int found = 0;
        int root = 0;
 
        scanf("%d", &n);
 
        prime_list = malloc(sizeof(int) * n / 2);
        prime_list[0] = 2;
        prime_list[1] = 3;
        prime_list[2] = 5;
        size = 3;
 
        if (n > 0)
        {
                printf("%d\n", 2);
        }
        if (n > 1)
        {
                printf("%d\n", 3);
        }
        if (n > 2)
        {
                printf("%d\n", 5);
        }
        for ( i = 7 ; i < n ; i += 2 )
        {
                if (i % 10 == 5)
                {
                        continue;
                }
                root = sqrt(i);
                for ( j = 0 ; j < size ; j++ )
                {
                        if ( prime_list[j] > root )
                        {
                                found = 0;
                                break;
                        }
                        else if ( i % prime_list[j] == 0 )
                        {
                                found = 1;
                                break;
                        }
                }
                if ( !found )
                {
                        prime_list[size++] = i;
                        printf("%d\n", i);
                }
        }
 
        return 0;
}

• 참고 : 멀티스레드 소수 구하기
  • http://devnote.net/wiki/index.php?title=%EB%A9%80%ED%8B%B0_%EC%8A%A4%EB%A0%88%EB%93%9C_%ED%94%84%EB%A1%9C%EA%B7%B8%EB%9E%A8_%EC%98%88%EC%A0%9C&printable=yes
  • 속도는 빠를수도 있으나 그리 유용하지는 않네요 ^^;