快速计算素数程序

Wheel factorization

Wheel factorization是一种生成素数方法。

对于大于30的数，只有30n+1,30n+7,30n+11,30n+13,30n+17,30n+19,30n+23,30n+29才可能是素数，这里n>=1。

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

#define NUM_O_PRIMES    2015
long primes1[NUM_O_PRIMES];

void primes()
{
    int base = 30, pc = 0, column[] = {1, 7, 11, 13, 17, 19, 23, 29};

    int pp = 0;
    primes1[pp++] = 2;
    primes1[pp++] = 3;
    primes1[pp++] = 5;
    primes1[pp++] = 7;
    primes1[pp++] = 11;
    primes1[pp++] = 13;
    primes1[pp++] = 17;
    primes1[pp++] = 19;
    primes1[pp++] = 23;
    primes1[pp++] = 29;

     while(pp < NUM_O_PRIMES)
    {
        if(pc == 8)
        {
            base += 30;
            pc = 0;
        }

        long p, q;
        p = base + column[pc++];
        q = sqrt(p);
        int j = 3;
        while(primes1[j] <= q)
        {
            if(p % primes1[j] == 0)
                break;
            j++;
        }
        if(primes1[j] > q)
            primes1[pp++] = p;
  }
}

int main(void)
{
     primes();
     int i;
     for(i=0; i<NUM_O_PRIMES; i++)
     {
        printf("%d:%ld
", i+1, primes1[i]);
     }
    return 0;
}